First: I have ColorChecker and MiniColorChecker and I understand they
correspond to the same LAB values - is this true?
Second: I have, in controlled conditions (using a softbox at about 15
feet away from the target, the light perpendicular to the target, and
my camera placed at the exact same height as the center of the target
and also about 15 feet away but making a 25-35 degree angle with
respect to the softbox light direction) achieved DE 2000 of 1.33 which
is as I understand very close to exceptional. This is all very nice,
but when I take my target (either) outdoors on a sunny day, a
Third: what geometrical arrangement should I use to place my target
with respect to the sun (rays perpendicular to target?), and how or
where and how far should I place my camera? In looking for uniform
lighting I have come to the conclusion that the sun's rays must be
perpendicular to the target and that, since the camera cannot be
perpendicular to the target, then the closest approximation is to take
an angle (perhaps 25-35 degrees or what is your suggestion on this?)
and to move the camera away far enough so that the difference in the
angle made with respect to one side of the target and the angle made
with respect to the other farther away side, is minimized. Also, when
these two angles are almost the same then the sun's reflection from
each extreme should be very similar. Is this line of reasoning
correct? Should I instead place the target to make an equal angle to
the sun and to my camera? The problem I see with these is a lot of
glare in the image... Not sure though...
Fourth: if the sun is fully shining with no clouds beneath it, does it
matter is there are white clouds (not stormy or dark) in other places
in the sky?
Fifth: I keep getting very good matches in the hues of RGB patches but
the saturation constantly becomes a problem - the script has a lot of
trouble getting a good value for the RGB saturation. Why is this and
what can I do to obtain saturation values closer to ideal?
Sixth: I have been using the ACR_Calibrator_CC24 V6.4 by Rags Gardner,
which is also based on Fors' script, and my camera is Canon EOS 1Ds
MIII.
Thanks in advance to any responses. I have tried to be very precise in
my questions and what I have tried, in the hope that this might make
it easier to answer.
Something is missing from your initial list of questions in that it jumps
from the middle of a sentence ending with "a" in First to the beginning of
Third.
I believe the two targets are supposed to be the same as far as colors. I
wouldn't be surprised if they use the same pigments for each.
The matte finish of the target will pick up color from anywhere in front of
it, so trees and grass and blue sky and sun and your clothes and the color
of buildings, etc.
There is no single correct answer to what angle the target and lightsource
and camera should be although there are probably some obviously wrong
configurations: no glare, no shadows, no uneven illuminations, minimize
envronmental reflections unless they will be significantly contributing to
the overall lighting in the actual situation--tilt up toward the sky more
than down toward the grass (unless your subject is very close to the grass
or tree or green plants so their skin will and away from, not toward a large
green tree or brick house, etc. Realize that the lighting that you are
optimizing for is usually a mixture of sky and sun. To minimize glare I try
to make the angle of the camera-target-sun so that if the target was a
mirror then the imagined reflection would only be blue sky away from any sun
and away from any trees or buildings.
Outdoors I usually do things in one of two ways, either:
1) With the sun relatively high, I lay the target flat on the
pavement/sidewalk, away from any trees or buildings, and usually shoot it
somewhere between 45 and 60 (closer to over-top) and have the sun over to
one side quite a ways just to minimize any glare. I have it pointing
straight up so I only have sky and sun light on it, and no grass or
non-neutral pavement coloring the light. If it's cloudy then the angle to
the sun isn't important, but any environmental things like trees and
buildings are so I'd want the open cloudy-sky as
2) With the sun relatively low, I hold the target in one hand at a
45-to-60-degree angle (more vertical than horizontal) with the sun over my
shoulder 30 degrees to the side to keep my shadow out of it and hold the
camera and take the picture with the other hand. I use this method for low
sun because the color of the sun will be different and there will likely be
glare coming off the ground/grass/pavement between the sun and the subject
that will color the light even more so I can to accurately measure and
calibrate for this color.
Another special outdoor situation would be within a forest where the light
is diffuse and colored by the greenery around or a variation of this would
be in a flower garden where there are lots of plants and many different
colors of flowers. You would want to probably keep the target more vertical
to pick up the green being reflected from the ground as much as the blue
from the sky. Of course this doesn't apply if you are using a large
reflector below, so the reflected sky and sun is what is illuminating the
face. The same sort of thing might be true if your subject was standing on
any very non-neutral-colored surface such as a brick path, or next to a
brick building, although the red from bricks might just make the skin look
better, so wouldn't need to be accomidated for, but green grass or forest
folage are another story--you don't want the skin to look green, usually.
In a studio situation, which means I have control over all the lighting and
the environment (walls floor ceiling) is neutral (black/gray/white) colored,
and where I am calibrating for the particular lighting, specifically, I
would face the target relatively perpendicular to (flat to) the camera
(perhaps slightly off just to keep any reflections from me out of it) and
have the lighting at wherever angles they are going to be at. This assumes
the part of the subject or object facing the camera is the most important
part. If I were doing something odd, such as having the key light very far
over to the side, I'd probably want to angle the target more toward the key
light just so it was still the main light source being balanced for.
Nowadays, in a studio-lighting situation, instead of doing a custom
calibration for each lighting setup, I would create a custom DNG camera
profile (LR 2+, PS CS3+ with latest ACR) for each light source. I would
create it with both color-tables using the same CC photo so no interplation
would be occuring.
And also, nowadays, for non-studio things, I have a two light-source
(Incandescent and Cloudy) DNG Camera Profile I have created with the two
color tables based on two different RAWs and don't use the camera
calibration sliders, nor these scripts, anymore.
One unfortunate thing about the ACR/LR profiles you're trying to calibrate
against, is that they are dual light-source profiles that are for
approximately 2700K (Tungsten) and 6500K (Cloudy) and the effective camera
profile that is being used for a particular white-balance in between those
two color temperatures will be an interpolation of those two internal
profiles, and you have to have a different calibration for each WB between
those two color temperatures--at least have to have several. If your WB is
at or below 2700K or at or above 6500K then only one profile would be used
and a single calibration would be valid for a wider range of WBs. In
practice I have found that Sunny (5500K and above calibrations are very
similar so I would tend to use a Cloudy (6500K) calibration for sunny and
bluer, and only worry about multiple calibrations for lighting redder than
Sunlight, except for very blue lighting, such as moonlight or twilight.
I wouldn't use Rags' or Fors' scripts because the only use three of the
color patches (R, G, B) to calibrate the color againt. I would use
Tindemans' where you can have it use all the color patches.
I'm not sure what you're saying regarding saturation, but maybe it is that
saturation is a function of contrast so if your contrast or black point or
contrast (toning) curve settings are different between your calibration and
your real-world shots then your real-world shots will have a different
saturation compared to the calibration shots. If you always use the ACR
defaults for your RAW conversions then you can calibrate to those and have
less change, but the calibration default for the toning curve is something
non-linear which makes the contrast of midtones higher than the contrast of
darks and lights so calibrating using only three mid-tone RGB patches will
make the shadows and highlights less contrasty and look less saturated,
although perhaps that is what you'd usually want to occur. I know Fors'
script resets the toning curve to linear and so using any Fors calibratoin
with a non-linear toning curve will have overly saturated colors. I usually
like this look, as my shots are nature not people, but your situation may be
different.
On Fri, Nov 21, 2008 at 10:46 AM, Juan <juan_d...@hotmail.com> wrote:
> Hi,
> First: I have ColorChecker and MiniColorChecker and I understand they
> correspond to the same LAB values - is this true?
> Second: I have, in controlled conditions (using a softbox at about 15
> feet away from the target, the light perpendicular to the target, and
> my camera placed at the exact same height as the center of the target
> and also about 15 feet away but making a 25-35 degree angle with
> respect to the softbox light direction) achieved DE 2000 of 1.33 which
> is as I understand very close to exceptional. This is all very nice,
> but when I take my target (either) outdoors on a sunny day, a
> Third: what geometrical arrangement should I use to place my target
> with respect to the sun (rays perpendicular to target?), and how or
> where and how far should I place my camera? In looking for uniform
> lighting I have come to the conclusion that the sun's rays must be
> perpendicular to the target and that, since the camera cannot be
> perpendicular to the target, then the closest approximation is to take
> an angle (perhaps 25-35 degrees or what is your suggestion on this?)
> and to move the camera away far enough so that the difference in the
> angle made with respect to one side of the target and the angle made
> with respect to the other farther away side, is minimized. Also, when
> these two angles are almost the same then the sun's reflection from
> each extreme should be very similar. Is this line of reasoning
> correct? Should I instead place the target to make an equal angle to
> the sun and to my camera? The problem I see with these is a lot of
> glare in the image... Not sure though...
> Fourth: if the sun is fully shining with no clouds beneath it, does it
> matter is there are white clouds (not stormy or dark) in other places
> in the sky?
> Fifth: I keep getting very good matches in the hues of RGB patches but
> the saturation constantly becomes a problem - the script has a lot of
> trouble getting a good value for the RGB saturation. Why is this and
> what can I do to obtain saturation values closer to ideal?
> Sixth: I have been using the ACR_Calibrator_CC24 V6.4 by Rags Gardner,
> which is also based on Fors' script, and my camera is Canon EOS 1Ds
> MIII.
> Thanks in advance to any responses. I have tried to be very precise in
> my questions and what I have tried, in the hope that this might make
> it easier to answer.
Thanks for such a complete response. I have some doubts about your
suggestions.
when you say "usually shoot it somewhere between 45 and 60 (closer to
over-top) and have the sun over to
one side quite a ways just to minimize any glare" , can you be more
precise as to what you mean by have the sun over to one side?
Say your camera makes an angle of 45-60 with respect to the ground and
say south (just for reference) of the target, does the sun need to be
north or towards the east or west (whichever side the sun happens to
be)?
How high over the horizon do you mean by "the sun relatively high"?
More than 30 or 45 degrees above horizon?
Now, if environmental things like trees, are going to be in front of
the subject, then shouldn´t we place the target to include those trees
- in order to really get the same lighting that the subject will get?
Now, the other point: "With the sun relatively low, I hold the target
in one hand at a 45-to-60-degree angle (more vertical than horizontal)
with the sun over my shoulder 30 degrees to the side", I am sorry to
ask but how are you measuring your angle? Do you mean between the sun
rays and the target surface? In that case, placing the target
perpendicular (fully facing the sun) would make a 90 degree angle. If
I interpret this correctly, then 45-60 angle will make the target
approximately face the horizon assuming a low sun. This is a concern
because it would take light from the ground as well as the sun and
then we are back at my previous question: should we face the target at
all light emitting (or reflecting) sources that will also reach my
subject?
Also, when you say: "bluer, and only worry about multiple calibrations
for lighting redder than Sunlight, except for very blue lighting, such
as moonlight or twilight", do you mean that you create several DNG
profiles specific for these uncontrolled lighting, not trusting the 2
profile system that Adobe has come up with? You say calibrations but I
guess you meant DNG profiles, right?
And, "I'm not sure what you're saying regarding saturation, but maybe
it is that saturation is a function of contrast so if your contrast or
black point or contrast (toning) curve settings are different between
your calibration". What do I make of this? It has been told that the
tone should be linear in order to get more precise calibrations with
the scripts and I always do the calibrations with linear tone curve.
Yet, I see the scripts having great difficulty in reaching a
satisfactory saturation. I don´t quite understand this??
Finally, and probably the most important question: what ProPhoto RGB
or LAB values should I expose the white patch for? Is it 241,241,241?
Again, thanks a million for your preciseness and patience.
Best regards,
Juan Dent
On Nov 21, 2:10 pm, "steve sprengel" <steve.spren...@gmail.com> wrote:
> Something is missing from your initial list of questions in that it jumps
> from the middle of a sentence ending with "a" in First to the beginning of
> Third.
> I believe the two targets are supposed to be the same as far as colors. I
> wouldn't be surprised if they use the same pigments for each.
> The matte finish of the target will pick up color from anywhere in front of
> it, so trees and grass and blue sky and sun and your clothes and the color
> of buildings, etc.
> There is no single correct answer to what angle the target and lightsource
> and camera should be although there are probably some obviously wrong
> configurations: no glare, no shadows, no uneven illuminations, minimize
> envronmental reflections unless they will be significantly contributing to
> the overall lighting in the actual situation--tilt up toward the sky more
> than down toward the grass (unless your subject is very close to the grass
> or tree or green plants so their skin will and away from, not toward a large
> green tree or brick house, etc. Realize that the lighting that you are
> optimizing for is usually a mixture of sky and sun. To minimize glare I try
> to make the angle of the camera-target-sun so that if the target was a
> mirror then the imagined reflection would only be blue sky away from any sun
> and away from any trees or buildings.
> Outdoors I usually do things in one of two ways, either:
> 1) With the sun relatively high, I lay the target flat on the
> pavement/sidewalk, away from any trees or buildings, and usually shoot it
> somewhere between 45 and 60 (closer to over-top) and have the sun over to
> one side quite a ways just to minimize any glare. I have it pointing
> straight up so I only have sky and sun light on it, and no grass or
> non-neutral pavement coloring the light. If it's cloudy then the angle to
> the sun isn't important, but any environmental things like trees and
> buildings are so I'd want the open cloudy-sky as
> 2) With the sun relatively low, I hold the target in one hand at a
> 45-to-60-degree angle (more vertical than horizontal) with the sun over my
> shoulder 30 degrees to the side to keep my shadow out of it and hold the
> camera and take the picture with the other hand. I use this method for low
> sun because the color of the sun will be different and there will likely be
> glare coming off the ground/grass/pavement between the sun and the subject
> that will color the light even more so I can to accurately measure and
> calibrate for this color.
> Another special outdoor situation would be within a forest where the light
> is diffuse and colored by the greenery around or a variation of this would
> be in a flower garden where there are lots of plants and many different
> colors of flowers. You would want to probably keep the target more vertical
> to pick up the green being reflected from the ground as much as the blue
> from the sky. Of course this doesn't apply if you are using a large
> reflector below, so the reflected sky and sun is what is illuminating the
> face. The same sort of thing might be true if your subject was standing on
> any very non-neutral-colored surface such as a brick path, or next to a
> brick building, although the red from bricks might just make the skin look
> better, so wouldn't need to be accomidated for, but green grass or forest
> folage are another story--you don't want the skin to look green, usually.
> In a studio situation, which means I have control over all the lighting and
> the environment (walls floor ceiling) is neutral (black/gray/white) colored,
> and where I am calibrating for the particular lighting, specifically, I
> would face the target relatively perpendicular to (flat to) the camera
> (perhaps slightly off just to keep any reflections from me out of it) and
> have the lighting at wherever angles they are going to be at. This assumes
> the part of the subject or object facing the camera is the most important
> part. If I were doing something odd, such as having the key light very far
> over to the side, I'd probably want to angle the target more toward the key
> light just so it was still the main light source being balanced for.
> Nowadays, in a studio-lighting situation, instead of doing a custom
> calibration for each lighting setup, I would create a custom DNG camera
> profile (LR 2+, PS CS3+ with latest ACR) for each light source. I would
> create it with both color-tables using the same CC photo so no interplation
> would be occuring.
> And also, nowadays, for non-studio things, I have a two light-source
> (Incandescent and Cloudy) DNG Camera Profile I have created with the two
> color tables based on two different RAWs and don't use the camera
> calibration sliders, nor these scripts, anymore.
> One unfortunate thing about the ACR/LR profiles you're trying to calibrate
> against, is that they are dual light-source profiles that are for
> approximately 2700K (Tungsten) and 6500K (Cloudy) and the effective camera
> profile that is being used for a particular white-balance in between those
> two color temperatures will be an interpolation of those two internal
> profiles, and you have to have a different calibration for each WB between
> those two color temperatures--at least have to have several. If your WB is
> at or below 2700K or at or above 6500K then only one profile would be used
> and a single calibration would be valid for a wider range of WBs. In
> practice I have found that Sunny (5500K and above calibrations are very
> similar so I would tend to use a Cloudy (6500K) calibration for sunny and
> bluer, and only worry about multiple calibrations for lighting redder than
> Sunlight, except for very blue lighting, such as moonlight or twilight.
> I wouldn't use Rags' or Fors' scripts because the only use three of the
> color patches (R, G, B) to calibrate the color againt. I would use
> Tindemans' where you can have it use all the color patches.
> I'm not sure what you're saying regarding saturation, but maybe it is that
> saturation is a function of contrast so if your contrast or black point or
> contrast (toning) curve settings are different between your calibration and
> your real-world shots then your real-world shots will have a different
> saturation compared to the calibration shots. If you always use the ACR
> defaults for your RAW conversions then you can calibrate to those and have
> less change, but the calibration default for the toning curve is something
> non-linear which makes the contrast of midtones higher than the contrast of
> darks and lights so calibrating using only three mid-tone RGB patches will
> make the shadows and highlights less contrasty and look less saturated,
> although perhaps that is what you'd usually want to occur. I know Fors'
> script resets the toning curve to linear and so using any Fors calibratoin
> with a non-linear toning curve will have overly saturated
By "over to the side or "around to the side' I mean at a different "heading" or "compass direction" than directly in front or behind. Using the old-fashioned clock-face analogy, if the clock face is flat on the ground, and the CC is in the center, and I am at the 6-o'clock position, facing the center and hence facing the 12-o'clock position, then in the example of the sun being high but in front of me (as if I am facing generally south in the northern hemisphere) then over to the side would be somewhere between the 10:00 and 11:00 or the 1:00 and 2:00 positions or between 30-60 degrees either counter-clockwise or clockwise. Directly in front of me would be the 12-o'clock position and I would assume too much glare would be reflecting to make an accurate reading. In the case when the sun is low and over my shoulder then it would be between the 4:30 to 5:30 or 6:30 to 7 position.
By the sun being relatively high I mean closer to mid-day than sun-rise or sunset.
If the trees in front of the subject are providing most of the light, and the sun, nor blue sky are not, then sure, use the target at the subject position facing somewhat upward, but the sun and even a cloudy sky is quite a bit brighter than what would be reflected by nearby trees that it would likely be a special case, unless you are actually under a tree canopy in a forest. Of course, determining the correct white-balance is much more important than having exactly the right calibration. You can test your theory about whether the trees are messing much with the calibration by doing one calibration with the CC facing the camera and one with is facing more upward so the sky and sun are more of the light compared to the trees and see how much different the calibration is.
As far as multiple calibrations for redder than sunlight or very blue like twilight then I mean multiple calibrations for redder than sunlight, assuming you are already using a dual 2650K-6500K profile, and could mean either multiple calibrations or multiple DNG Profiles for something very blue, which won't be covered in the range of a dual profile and is much bluer than then Cloudy 6500K.
I wasn't quite sure what you mean when you say "scripts having great difficulty reaching satisfactory saturation" so I just made general comments saturation issues that you can have when you use a linear curve to compute a profile but using something other than linear when you actually develop. Maybe you can explain more what you mean and I can say something else or may not actually know what to say.
If you look in the script you will see what the white-patch values are in ProPhotoRGB and I don't know what those are off hand. I wouldn't worry so much about the exposure being exactly 241, 241, 241 though if the whole thing is too bright or too dark. If you are letting the script optimize the neutral-patches then it should do what you want, otherwise maybe having the midtone close to what it's supposed to be is better than having one end what it should be.
From: Juan Sent: Friday, November 21, 2008 6:14 PM
To: AcrCalibrator Subject: [acrcal] Re: Frustration at not being able to get excellent results in outdoor conditions
HI,
Thanks for such a complete response. I have some doubts about your
suggestions.
when you say "usually shoot it somewhere between 45 and 60 (closer to
over-top) and have the sun over to
one side quite a ways just to minimize any glare" , can you be more
precise as to what you mean by have the sun over to one side?
Say your camera makes an angle of 45-60 with respect to the ground and
say south (just for reference) of the target, does the sun need to be
north or towards the east or west (whichever side the sun happens to
be)?
How high over the horizon do you mean by "the sun relatively high"?
More than 30 or 45 degrees above horizon?
Now, if environmental things like trees, are going to be in front of
the subject, then shouldn´t we place the target to include those trees
- in order to really get the same lighting that the subject will get?
Now, the other point: "With the sun relatively low, I hold the target
in one hand at a 45-to-60-degree angle (more vertical than horizontal)
with the sun over my shoulder 30 degrees to the side", I am sorry to
ask but how are you measuring your angle? Do you mean between the sun
rays and the target surface? In that case, placing the target
perpendicular (fully facing the sun) would make a 90 degree angle. If
I interpret this correctly, then 45-60 angle will make the target
approximately face the horizon assuming a low sun. This is a concern
because it would take light from the ground as well as the sun and
then we are back at my previous question: should we face the target at
all light emitting (or reflecting) sources that will also reach my
subject?
Also, when you say: "bluer, and only worry about multiple calibrations
for lighting redder than Sunlight, except for very blue lighting, such
as moonlight or twilight", do you mean that you create several DNG
profiles specific for these uncontrolled lighting, not trusting the 2
profile system that Adobe has come up with? You say calibrations but I
guess you meant DNG profiles, right?
And, "I'm not sure what you're saying regarding saturation, but maybe
it is that saturation is a function of contrast so if your contrast or
black point or contrast (toning) curve settings are different between
your calibration". What do I make of this? It has been told that the
tone should be linear in order to get more precise calibrations with
the scripts and I always do the calibrations with linear tone curve.
Yet, I see the scripts having great difficulty in reaching a
satisfactory saturation. I don´t quite understand this??
Finally, and probably the most important question: what ProPhoto RGB
or LAB values should I expose the white patch for? Is it 241,241,241?
Again, thanks a million for your preciseness and patience.
Best regards,
Juan Dent
On Nov 21, 2:10 pm, "steve sprengel" <steve.spren...@gmail.com> wrote:
> Something is missing from your initial list of questions in that it jumps
> from the middle of a sentence ending with "a" in First to the beginning of
> Third.
> I believe the two targets are supposed to be the same as far as colors. I
> wouldn't be surprised if they use the same pigments for each.
> The matte finish of the target will pick up color from anywhere in front of
> it, so trees and grass and blue sky and sun and your clothes and the color
> of buildings, etc.
> There is no single correct answer to what angle the target and lightsource
> and camera should be although there are probably some obviously wrong
> configurations: no glare, no shadows, no uneven illuminations, minimize
> envronmental reflections unless they will be significantly contributing to
> the overall lighting in the actual situation--tilt up toward the sky more
> than down toward the grass (unless your subject is very close to the grass
> or tree or green plants so their skin will and away from, not toward a large
> green tree or brick house, etc. Realize that the lighting that you are
> optimizing for is usually a mixture of sky and sun. To minimize glare I try
> to make the angle of the camera-target-sun so that if the target was a
> mirror then the imagined reflection would only be blue sky away from any sun
> and away from any trees or buildings.
> Outdoors I usually do things in one of two ways, either:
> 1) With the sun relatively high, I lay the target flat on the
> pavement/sidewalk, away from any trees or buildings, and usually shoot it
> somewhere between 45 and 60 (closer to over-top) and have the sun over to
> one side quite a ways just to minimize any glare. I have it pointing
> straight up so I only have sky and sun light on it, and no grass or
> non-neutral pavement coloring the light. If it's cloudy then the angle to
> the sun isn't important, but any environmental things like trees and
> buildings are so I'd want the open cloudy-sky as
> 2) With the sun relatively low, I hold the target in one hand at a
> 45-to-60-degree angle (more vertical than horizontal) with the sun over my
> shoulder 30 degrees to the side to keep my shadow out of it and hold the
> camera and take the picture with the other hand. I use this method for low
> sun because the color of the sun will be different and there will likely be
> glare coming off the ground/grass/pavement between the sun and the subject
> that will color the light even more so I can to accurately measure and
> calibrate for this color.
> Another special outdoor situation would be within a forest where the light
> is diffuse and colored by the greenery around or a variation of this would
> be in a flower garden where there are lots of plants and many different
> colors of flowers. You would want to probably keep the target more vertical
> to pick up the green being reflected from the ground as much as the blue
> from the sky. Of course this doesn't apply if you are using a large
> reflector below, so the reflected sky and sun is what is illuminating the
> face. The same sort of thing might be true if your subject was standing on
> any very non-neutral-colored surface such as a brick path, or next to a
> brick building, although the red from bricks might just make the skin look
> better, so wouldn't need to be accomidated for, but green grass or forest
> folage are another story--you don't want the skin to look green, usually.
> In a studio situation, which means I have control over all the lighting and
> the environment (walls floor ceiling) is neutral (black/gray/white) colored,
> and where I am calibrating for the particular lighting, specifically, I
> would face the target relatively perpendicular to (flat to) the camera
> (perhaps slightly off just to keep any reflections from
My comment on saturation and the scripts is that they here is where
the most deviation (largest errors) occur. By contrast, the hue
quickly reach the goals set in the dialog box of the script (and excel
them!).
I was very grateful for your careful explanation of your "over to the
side". In that regard, I wish you could confirm my interpretation:
1) I think you have said (please confirm) that as long as the sun
is high enough, the CC target is to be placed flat on the ground,
facing the sky
2) I also interpret that when the sun is low, the CC target is to
be placed more near vertical (although not completely vertical) so as
to look towards the low sun
Does it matter if the camera is not facing the CC target exactly
perpendicularly?
Does it matter if the sun is not facing the CC target exactly
perpendicularly?
On the subject of evaluating CC shots: how can we measure the shot´s
quality objectively? The scripts give some idea of how much of a good
job one has done, but the DNG profile editor does not give any
feedback as to how good (i.e. evenly lit, free of color casts, etc.) a
shot of the CC target we have done!
Again, much appreciated.
Best regards,
Juan Dent
On Nov 24, 10:35 pm, "Steve Sprengel" <st...@sprengels.com> wrote:
> By "over to the side or "around to the side' I mean at a different "heading" or "compass direction" than directly in front or behind. Using the old-fashioned clock-face analogy, if the clock face is flat on the ground, and the CC is in the center, and I am at the 6-o'clock position, facing the center and hence facing the 12-o'clock position, then in the example of the sun being high but in front of me (as if I am facing generally south in the northern hemisphere) then over to the side would be somewhere between the 10:00 and 11:00 or the 1:00 and 2:00 positions or between 30-60 degrees either counter-clockwise or clockwise. Directly in front of me would be the 12-o'clock position and I would assume too much glare would be reflecting to make an accurate reading. In the case when the sun is low and over my shoulder then it would be between the 4:30 to 5:30 or 6:30 to 7 position.
> By the sun being relatively high I mean closer to mid-day than sun-rise or sunset.
> If the trees in front of the subject are providing most of the light, and the sun, nor blue sky are not, then sure, use the target at the subject position facing somewhat upward, but the sun and even a cloudy sky is quite a bit brighter than what would be reflected by nearby trees that it would likely be a special case, unless you are actually under a tree canopy in a forest. Of course, determining the correct white-balance is much more important than having exactly the right calibration. You can test your theory about whether the trees are messing much with the calibration by doing one calibration with the CC facing the camera and one with is facing more upward so the sky and sun are more of the light compared to the trees and see how much different the calibration is.
> As far as multiple calibrations for redder than sunlight or very blue like twilight then I mean multiple calibrations for redder than sunlight, assuming you are already using a dual 2650K-6500K profile, and could mean either multiple calibrations or multiple DNG Profiles for something very blue, which won't be covered in the range of a dual profile and is much bluer than then Cloudy 6500K.
> I wasn't quite sure what you mean when you say "scripts having great difficulty reaching satisfactory saturation" so I just made general comments saturation issues that you can have when you use a linear curve to compute a profile but using something other than linear when you actually develop. Maybe you can explain more what you mean and I can say something else or may not actually know what to say.
> If you look in the script you will see what the white-patch values are in ProPhotoRGB and I don't know what those are off hand. I wouldn't worry so much about the exposure being exactly 241, 241, 241 though if the whole thing is too bright or too dark. If you are letting the script optimize the neutral-patches then it should do what you want, otherwise maybe having the midtone close to what it's supposed to be is better than having one end what it should be.
> From: Juan
> Sent: Friday, November 21, 2008 6:14 PM
> To: AcrCalibrator
> Subject: [acrcal] Re: Frustration at not being able to get excellent results in outdoor conditions
> HI,
> Thanks for such a complete response. I have some doubts about your
> suggestions.
> when you say "usually shoot it somewhere between 45 and 60 (closer to
> over-top) and have the sun over to
> one side quite a ways just to minimize any glare" , can you be more
> precise as to what you mean by have the sun over to one side?
> Say your camera makes an angle of 45-60 with respect to the ground and
> say south (just for reference) of the target, does the sun need to be
> north or towards the east or west (whichever side the sun happens to
> be)?
> How high over the horizon do you mean by "the sun relatively high"?
> More than 30 or 45 degrees above horizon?
> Now, if environmental things like trees, are going to be in front of
> the subject, then shouldn´t we place the target to include those trees
> - in order to really get the same lighting that the subject will get?
> Now, the other point: "With the sun relatively low, I hold the target
> in one hand at a 45-to-60-degree angle (more vertical than horizontal)
> with the sun over my shoulder 30 degrees to the side", I am sorry to
> ask but how are you measuring your angle? Do you mean between the sun
> rays and the target surface? In that case, placing the target
> perpendicular (fully facing the sun) would make a 90 degree angle. If
> I interpret this correctly, then 45-60 angle will make the target
> approximately face the horizon assuming a low sun. This is a concern
> because it would take light from the ground as well as the sun and
> then we are back at my previous question: should we face the target at
> all light emitting (or reflecting) sources that will also reach my
> subject?
> Also, when you say: "bluer, and only worry about multiple calibrations
> for lighting redder than Sunlight, except for very blue lighting, such
> as moonlight or twilight", do you mean that you create several DNG
> profiles specific for these uncontrolled lighting, not trusting the 2
> profile system that Adobe has come up with? You say calibrations but I
> guess you meant DNG profiles, right?
> And, "I'm not sure what you're saying regarding saturation, but maybe
> it is that saturation is a function of contrast so if your contrast or
> black point or contrast (toning) curve settings are different between
> your calibration". What do I make of this? It has been told that the
> tone should be linear in order to get more precise calibrations with
> the scripts and I always do the calibrations with linear tone curve.
> Yet, I see the scripts having great difficulty in reaching a
> satisfactory saturation. I don´t quite understand this??
> Finally, and probably the most important question: what ProPhoto RGB
> or LAB values should I expose the white patch for? Is it 241,241,241?
> Again, thanks a million for your preciseness and patience.
> Best regards,
> Juan Dent
> On Nov 21, 2:10 pm, "steve sprengel" <steve.spren...@gmail.com> wrote:
> > Something is missing from your initial list of questions in that it jumps
> > from the middle of a sentence ending with "a" in First to the beginning of
> > Third.
> > I believe the two targets are supposed to be the same as far as colors. I
> > wouldn't be surprised if they use the same pigments for each.
> > The matte finish of the target will pick up color from anywhere in front of
> > it, so trees and grass and blue sky and sun and your clothes and the color
> > of buildings, etc.
> > There is no single correct answer to what angle the target and lightsource
> > and camera should be although there are probably some obviously wrong
> > configurations: no glare, no shadows, no uneven illuminations, minimize
> > envronmental reflections unless they will be significantly contributing to
> > the overall lighting in the actual situation--tilt up toward the sky more
> > than down toward the grass (unless your subject is very close to the grass
> > or tree or green plants so their skin will and away from, not toward a large
> > green tree or brick house, etc. Realize that the lighting that you are
> > optimizing for is usually a mixture of sky and sun. To minimize glare I try
> > to make the angle of the camera-target-sun so that if the target was a
> > mirror then the imagined reflection would only be blue sky away from any sun
> > and away from any trees or buildings.
> > Outdoors I usually do things in one of two ways, either:
> > 1) With the sun relatively high, I lay the target flat on the
> > pavement/sidewalk, away from any trees or buildings, and usually shoot it
> > somewhere between 45 and 60 (closer to over-top) and have the sun over to
> > one side quite a ways just to minimize any glare. I have it pointing
> > straight up so I only have sky and sun light on it, and no grass or
> > non-neutral pavement coloring the light. If it's cloudy then the angle to
> > the sun isn't important, but any environmental things like trees and
> > buildings are so I'd want the open cloudy-sky as
> > 2) With the sun relatively low, I hold the target in one hand at a
> > 45-to-60-degree angle (more vertical than horizontal) with the sun over my
> > shoulder 30 degrees to the side to keep my shadow out of it and hold the
> > camera and take the picture with the other hand. I use this method for low
> > sun because the color of the sun
"The CC target *is to be* placed flat on the ground" is a bit strong. My yard has big trees, but south of me there aren't so I typically place my CC flat on the ground and stand north of it, with the sun south of it, over to the side, and take my calibration shot. In a different location I might prop it up a bit at and angle with the important thing in whatever the situation is, is that the sky is what would be a reflection if the CC was a mirror instead of a matte-finish color-target, and that the sun is not glaring directly into the camera from the target, which can be judged by the glare not coming from the shiny black border area between the colored squares.
Except when the sun is low and the glare from the ground is also coloring the light, then I hold the target so it is almost glaring from the sun and the ground. It probably depends a bit on the orientation of your subject in this case, though. If you are photographing a person near camera height their face toward the sun, then having the target also mostly facing the sun would seem right. However, if you are photographing someone laying down on the ground with the sun hardly illuminating them at all, and the light is mostly coming from the darkening blue sky then it is more like shade lighting and I'd do that calbratoin with the target facing mostly upwards like their face is.
As far as perpendicular, the target and the sun never are for me, and if they both were, then my shadow would be on the target. It probably doesn't hurt to have the sun perpendicular to the target, but the camera probably shouldn't be, at least outside where the light is coming from above, because the camera and photographer would likely be blocking quite a bit of the sky from the target and giving the target more of a reddish sun-color compared to the blue-sky color where "sunny" should be a mixture of the two. About the only time I can think when the camera and the target are relatively perpendicular is indoors in the studio where there is balance lighting coming from both sides, and the model is holding the target mostly toward the camera, although it still wouldn't hurt to have it angled up slightly since the lighting is coming from slightly above--in the normal case, at least. Both the scripts and the DNG Profile Editor can handle a non-rectangular shape so having the camera perpendicular is not necessary.
I don't know if your saturation-error experience is different than mine or not, except to say that if your numbers are ending up at -100 or +100 then something is wrong. It probably depends, somewhat, on the particular camera. the particular color of light, the age and condition of the color-checker you're using, and the emphasis Adobe chose to put on various aspects of the color-profile you are calibrating against. If you have used LR 2 or ACR 4.6+ with the Adobe's camera-matching profiles (now just released from being non-beta) then you will see how much variation there is between different ones that try to emphasis certain colors, either to make them more saturated or to make them more accurate. I have my default calibration in Lightroom and ACR set to a dual-color custom profile that I've named 2700K-6500K (for obviously reasons) but sometimes I switch to one of the camera-matching profiles: Neutral or Landscape or Portrait, depending on which I like the best for the colors in the shot. The Landscape profile typically emphases certain colors that make outdoor shots without people look more like the bright colors of a picture-postcard postcard but would make people look much too colorful so I don't use it with indoor shots or portraits, usually.
As far as measuring the accuracy of the calibration, the numbers you get out of the scripts as their running are for just the patches being compared, which for Tom and Rags are only three, and not the whole chart, but I think Rags has a script that looks at all the colors and gives some overall number and perhaps per-patch numbers, although I'm not exactly sure.
I use the less-expensive (but still not cheap) version of Imatest for gauging color accuracy of my calibrations or profiles. It gives several overall numbers representing color-error measured in several different ways, plus it gives a chart that shows the direction and size of the error for each color patch. It even has a way to look at a 3D model of the color-error. The color-checker image does need to be relatively rectangular, so I usually have to do some perspective correction in Photoshop before giving the chart to Imatest to analyze. During its analysis it will warn if the illumination is uneven and one of the plots shows the line across the neutral squares where if you see the tops of the "bars" as slanted, then you know there was vignetting or some other source of unevenness, and another one of the plots shows the exaggerated color of the neutral strip so you can see what colro casts there might have been, or how non-neutral the squares actually are. I think there is a trial version of Imatest you can download. The UI is a little weird because the program can do all sorts of fancy anlaysis and the developer wanted the best math libraries he could get, which didn't have the best UI, but it is usable. Imatest, itself, does all sorts of other analysis about lens sharpness and noise levels in images and things so that's why it is so expensive, where I only use it for the color-error because I don't want to spend the money on the professional test charts you need to gauge sharpness from.
You have, no doubt, seen these Imatest color-error plots on my webpages for:
The main takeaway is that the colors won't be perfect no matter how well you profile so don't be overly obsessed with it, except for the fun of it.
From: Juan Sent: Tuesday, November 25, 2008 6:15 PM
To: AcrCalibrator Subject: [acrcal] Re: Frustration at not being able to get excellent results in outdoor conditions
Hi Steve and thanks again.
My comment on saturation and the scripts is that they here is where
the most deviation (largest errors) occur. By contrast, the hue
quickly reach the goals set in the dialog box of the script (and excel
them!).
I was very grateful for your careful explanation of your "over to the
side". In that regard, I wish you could confirm my interpretation:
1) I think you have said (please confirm) that as long as the sun
is high enough, the CC target is to be placed flat on the ground,
facing the sky
2) I also interpret that when the sun is low, the CC target is to
be placed more near vertical (although not completely vertical) so as
to look towards the low sun
Does it matter if the camera is not facing the CC target exactly
perpendicularly?
Does it matter if the sun is not facing the CC target exactly
perpendicularly?
On the subject of evaluating CC shots: how can we measure the shot´s
quality objectively? The scripts give some idea of how much of a good
job one has done, but the DNG profile editor does not give any
feedback as to how good (i.e. evenly lit, free of color casts, etc.) a
shot of the CC target we have done!
Again, much appreciated.
Best regards,
Juan Dent
On Nov 24, 10:35 pm, "Steve Sprengel" <st...@sprengels.com> wrote:
> By "over to the side or "around to the side' I mean at a different "heading" or "compass direction" than directly in front or behind. Using the old-fashioned clock-face analogy, if the clock face is flat on the ground, and the CC is in the center, and I am at the 6-o'clock position, facing the center and hence facing the 12-o'clock position, then in the example of the sun being high but in front of me (as if I am facing generally south in the northern hemisphere) then over to the side would be somewhere between the 10:00 and 11:00 or the 1:00 and 2:00 positions or between 30-60 degrees either counter-clockwise or clockwise. Directly in front of me would be the 12-o'clock position and I would assume too much glare would be reflecting to make an accurate reading. In the case when the sun is low and over my shoulder then it would be between the 4:30 to 5:30 or 6:30 to 7 position.
> By the sun being relatively high I mean closer to mid-day than sun-rise or sunset.
> If the trees in front of the subject are providing most of the light, and the sun, nor blue sky are not, then sure, use the target at the subject position facing somewhat upward, but the sun and even a cloudy sky is quite a bit brighter than what would be reflected by nearby trees that it would likely be a special case, unless you are actually under a tree canopy in a forest. Of course, determining the correct white-balance is much more important than having exactly the right calibration. You can test your theory about whether the trees are messing much with the calibration by doing one calibration with the CC facing the camera and one with is facing more upward so the sky and sun are more of the light compared to the trees and see how much different the calibration is.
> As far as multiple calibrations for redder than sunlight or very blue like twilight then I mean multiple calibrations for redder than sunlight, assuming you are already using a dual 2650K-6500K profile, and could mean either multiple calibrations or multiple DNG Profiles for something very blue, which won't be covered in the range of a dual profile and is much bluer than then Cloudy 6500K.
> I wasn't quite sure what you mean when you say "scripts having great difficulty reaching satisfactory saturation" so I just made general comments saturation issues that you can have when you use a linear curve to compute a profile but using something other than linear when you actually develop. Maybe you can explain
In case you are online: you say camera-matching profiles are now just
released from being non-beta, do you have a link where to download
them? I haven't found them...
Thanks for the Imatest suggestion.
One last question (for a while): targets shot under tungsten lighting,
are they incapable of being as accurate as shots in daylight/cloudy/
softbox (5500K-6500K)?
I ran Rags script on 2 shots at 2650K and their DE 2000 error is
around 4.0 - horrible!!
Is this to be expected because the light is just not as complete?
Thanks!
Best regards,
Juan
On Nov 26, 1:40 pm, "Steve Sprengel" <st...@sprengels.com> wrote:
> "The CC target *is to be* placed flat on the ground" is a bit strong. My yard has big trees, but south of me there aren't so I typically place my CC flat on the ground and stand north of it, with the sun south of it, over to the side, and take my calibration shot. In a different location I might prop it up a bit at and angle with the important thing in whatever the situation is, is that the sky is what would be a reflection if the CC was a mirror instead of a matte-finish color-target, and that the sun is not glaring directly into the camera from the target, which can be judged by the glare not coming from the shiny black border area between the colored squares.
> Except when the sun is low and the glare from the ground is also coloring the light, then I hold the target so it is almost glaring from the sun and the ground. It probably depends a bit on the orientation of your subject in this case, though. If you are photographing a person near camera height their face toward the sun, then having the target also mostly facing the sun would seem right. However, if you are photographing someone laying down on the ground with the sun hardly illuminating them at all, and the light is mostly coming from the darkening blue sky then it is more like shade lighting and I'd do that calbratoin with the target facing mostly upwards like their face is.
> As far as perpendicular, the target and the sun never are for me, and if they both were, then my shadow would be on the target. It probably doesn't hurt to have the sun perpendicular to the target, but the camera probably shouldn't be, at least outside where the light is coming from above, because the camera and photographer would likely be blocking quite a bit of the sky from the target and giving the target more of a reddish sun-color compared to the blue-sky color where "sunny" should be a mixture of the two. About the only time I can think when the camera and the target are relatively perpendicular is indoors in the studio where there is balance lighting coming from both sides, and the model is holding the target mostly toward the camera, although it still wouldn't hurt to have it angled up slightly since the lighting is coming from slightly above--in the normal case, at least. Both the scripts and the DNG Profile Editor can handle a non-rectangular shape so having the camera perpendicular is not necessary.
> I don't know if your saturation-error experience is different than mine or not, except to say that if your numbers are ending up at -100 or +100 then something is wrong. It probably depends, somewhat, on the particular camera. the particular color of light, the age and condition of the color-checker you're using, and the emphasis Adobe chose to put on various aspects of the color-profile you are calibrating against. If you have used LR 2 or ACR 4.6+ with the Adobe's camera-matching profiles (now just released from being non-beta) then you will see how much variation there is between different ones that try to emphasis certain colors, either to make them more saturated or to make them more accurate. I have my default calibration in Lightroom and ACR set to a dual-color custom profile that I've named 2700K-6500K (for obviously reasons) but sometimes I switch to one of the camera-matching profiles: Neutral or Landscape or Portrait, depending on which I like the best for the colors in the shot. The Landscape profile typically emphases certain colors that make outdoor shots without people look more like the bright colors of a picture-postcard postcard but would make people look much too colorful so I don't use it with indoor shots or portraits, usually.
> As far as measuring the accuracy of the calibration, the numbers you get out of the scripts as their running are for just the patches being compared, which for Tom and Rags are only three, and not the whole chart, but I think Rags has a script that looks at all the colors and gives some overall number and perhaps per-patch numbers, although I'm not exactly sure.
> I use the less-expensive (but still not cheap) version of Imatest for gauging color accuracy of my calibrations or profiles. It gives several overall numbers representing color-error measured in several different ways, plus it gives a chart that shows the direction and size of the error for each color patch. It even has a way to look at a 3D model of the color-error. The color-checker image does need to be relatively rectangular, so I usually have to do some perspective correction in Photoshop before giving the chart to Imatest to analyze. During its analysis it will warn if the illumination is uneven and one of the plots shows the line across the neutral squares where if you see the tops of the "bars" as slanted, then you know there was vignetting or some other source of unevenness, and another one of the plots shows the exaggerated color of the neutral strip so you can see what colro casts there might have been, or how non-neutral the squares actually are. I think there is a trial version of Imatest you can download. The UI is a little weird because the program can do all sorts of fancy anlaysis and the developer wanted the best math libraries he could get, which didn't have the best UI, but it is usable. Imatest, itself, does all sorts of other analysis about lens sharpness and noise levels in images and things so that's why it is so expensive, where I only use it for the color-error because I don't want to spend the money on the professional test charts you need to gauge sharpness from.
> You have, no doubt, seen these Imatest color-error plots on my webpages for:
> The main takeaway is that the colors won't be perfect no matter how well you profile so don't be overly obsessed with it, except for the fun of it.
> From: Juan
> Sent: Tuesday, November 25, 2008 6:15 PM
> To: AcrCalibrator
> Subject: [acrcal] Re: Frustration at not being able to get excellent results in outdoor conditions
> Hi Steve and thanks again.
> My comment on saturation and the scripts is that they here is where
> the most deviation (largest errors) occur. By contrast, the hue
> quickly reach the goals set in the dialog box of the script (and excel
> them!).
> I was very grateful for your careful explanation of your "over to the
> side". In that regard, I wish you could confirm my interpretation:
> 1) I think you have said (please confirm) that as long as the sun
> is high enough, the CC target is to be placed flat on the ground,
> facing the sky
> 2) I also interpret that when the sun is low, the CC target is to
> be placed more near vertical (although not completely vertical) so as
> to look towards the low sun
> Does it matter if the camera is not facing the CC target exactly
> perpendicularly?
> Does it matter if the sun is not facing the CC target exactly
> perpendicularly?
> On the subject of evaluating CC shots: how can we measure the shot´s
> quality objectively? The scripts give some idea of how much of a good
> job one has done, but the DNG profile editor does not give any
> feedback as to how good (i.e. evenly lit, free of color casts, etc.) a
> shot of the CC target we have done!
> Again, much appreciated.
> Best regards,
> Juan Dent
> On Nov 24, 10:35 pm, "Steve Sprengel" <st...@sprengels.com> wrote:
> > By "over to the side or "around to the side' I mean at a different "heading" or "compass direction" than directly in front or behind. Using the old-fashioned clock-face analogy, if the clock face is flat on the ground, and the CC is in the center, and I am at the 6-o'clock position, facing the center and hence facing the 12-o'clock position, then in the example of the sun being high but in front of me (as if I am facing generally south in the northern hemisphere) then over to the side would be somewhere between the 10:00 and 11:00 or the 1:00 and 2:00 positions or between 30-60 degrees either counter-clockwise or clockwise. Directly in front of me would be the 12-o'clock position and I would assume too much glare would be reflecting to make an accurate reading. In the case when the sun is low and over my shoulder then it would be between the 4:30 to 5:30 or 6:30 to 7 position.
> > By the sun being relatively high I mean closer to mid-day than sun-rise or sunset.
> > If the trees in front of the subject are providing most of the light, and the sun, nor blue sky are not, then sure, use the target at the subject position facing somewhat upward, but the sun and even a cloudy sky is quite a bit brighter than what would be reflected by nearby trees that it would likely be a special case, unless you are actually under a tree canopy in a forest. Of course, determining the correct white-balance is much more important than having exactly the right calibration. You can test your theory about whether the trees are messing much with the calibration by doing one calibration with the CC facing the camera and one with is facing more upward so the sky and sun are more of the light compared to the trees and
The new, non-beta Adobe camera-matching profiles install when you install the latest DNG Converter and perhaps CS4's/ACR 5.2. I became aware of this information because I subscribe to the messages from the Adobe Lightroom Forums where someone posted a message there:
http://www.adobeforums.com/webx?13@@.59b71b41
where you have to change the drop-down-list at the top to DNG Converter to get just it, and not ACR along with it unless you have CS4 then the combined one is good. LR 2.2 will be out in a week or two, I guess, but the profiles are visible in 2.1, just not the new camera support, yet.
[That first part was easy, but you asked a question that requires more explanation so I am taking more time to write it.]
As far as the error with incandescent lighting, I think this has to do with the particular colors of the color-checker as being across the entire spectrum and the scripts' internal "ideal" standard CC values are for either D50 (Sunny) or D65 (Cloudy) lighting (I forget), but not for Illuminant A (tungsten).
The main issue photographing something with many colors (like the CC) under lighting with bias towards a particular set of colors (reddish ones for tungsten) is that a colored light will neutralize colors that are similar to it once you white balance for the color of the lighting. White-balancing is basically draining the color of the light from all the colors in the image, which will undersaturate the colors that are similar to the color of the light and oversaturate the colors that are opposite it and this will make the color error among the various color-patches uneven as compared to the ideal D50 (or D65) standard values. A wild-card in all of this is that Adobe's Incandescent end of their dual profile is likely optimized for skin tones so it is hard to guess where the color-error will be but there will likely be more for Incandescent than the Sunny/Cloudy because the color-error is being computed with respect to the D50/D65 color values, not Illuminant-A color values. It would be impossible to use these scripts to compute an actual color profile because the internal standard is for D50 or D60 lighting only, but you can assume that the color profile Adobe provides has already taken the lighting color into account--after all they can compute their own standard values for the CC patches in different lighting using an actual spectrophotometer and shouldn't have to rely on published values. So a calibration script is merely correcting values that should be mostly corrected for the lighting color already. However, as was previously said, the Incandescent profile is likely optimized for skin tones so there is more color-error in it, overall, and the scripts just can't neutralize it all. You can assume that if you use the DNG Profile Editor and create a dual-color profile that Adobe has used the ideal values for 2650K when you compute that color-table and 6500K when you compute that color table so your DNG Profile will likely be closer than the Adobe Standard that should be optimized for skin tones.
The one lesson I can learn from doing my own calibrations is that I want to include Yellow along with red, green, and blue, when I calibrate for incandescent because yellow has been the most off after I calibrate if I don't.
Look at the 2700K+1 color-error sequence and notice how far off the "top" yellowish colors are after running Tom Fors' script -- the third panel over, as compared to how relatively close things are if I optimize the color error in RGB and CMY -- the fourth panel over:
You will notice how close I got using the DNG profile editor for 2700K lighting, where mostly the Red square is a bit oversaturated (circle further away from the center than the square), using either the DNG Profile editor dual profile on the 2700K end, or a single color table profile made specifically for 2700K:
In the 6500K sequence you will notice the Tindemans got better results than the DNG Profile Editor, but you will also notice that the circles directly in the middle (which correspond to the neutral row) aren't aligned above each other, so there was likely some color-cast that affected the dark areas differently than the light areas, but 6500K is hard to get, exactly, using only sun and clouds outdoors (which is all I have) so I haven't been able to reshoot to see if that helps make the neutrals more in line.
From: Juan Sent: Wednesday, November 26, 2008 2:35 PM
To: AcrCalibrator Subject: [acrcal] Re: Frustration at not being able to get excellent results in outdoor conditions
HI Steve,
In case you are online: you say camera-matching profiles are now just
released from being non-beta, do you have a link where to download
them? I haven't found them...
Thanks for the Imatest suggestion.
One last question (for a while): targets shot under tungsten lighting,
are they incapable of being as accurate as shots in daylight/cloudy/
softbox (5500K-6500K)?
I ran Rags script on 2 shots at 2650K and their DE 2000 error is
around 4.0 - horrible!!
Is this to be expected because the light is just not as complete?
Thanks!
Best regards,
Juan
On Nov 26, 1:40 pm, "Steve Sprengel" <st...@sprengels.com> wrote:
> "The CC target *is to be* placed flat on the ground" is a bit strong. My yard has big trees, but south of me there aren't so I typically place my CC flat on the ground and stand north of it, with the sun south of it, over to the side, and take my calibration shot. In a different location I might prop it up a bit at and angle with the important thing in whatever the situation is, is that the sky is what would be a reflection if the CC was a mirror instead of a matte-finish color-target, and that the sun is not glaring directly into the camera from the target, which can be judged by the glare not coming from the shiny black border area between the colored squares.
> Except when the sun is low and the glare from the ground is also coloring the light, then I hold the target so it is almost glaring from the sun and the ground. It probably depends a bit on the orientation of your subject in this case, though. If you are photographing a person near camera height their face toward the sun, then having the target also mostly facing the sun would seem right. However, if you are photographing someone laying down on the ground with the sun hardly illuminating them at all, and the light is mostly coming from the darkening blue sky then it is more like shade lighting and I'd do that calbratoin with the target facing mostly upwards like their face is.
> As far as perpendicular, the target and the sun never are for me, and if they both were, then my shadow would be on the target. It probably doesn't hurt to have the sun perpendicular to the target, but the camera probably shouldn't be, at least outside where the light is coming from above, because the camera and photographer would likely be blocking quite a bit of the sky from the target and giving the target more of a reddish sun-color compared to the blue-sky color where "sunny" should be a mixture of the two. About the only time I can think when the camera and the target are relatively perpendicular is indoors in the studio where there is balance lighting coming from both sides, and the model is holding the target mostly toward the camera, although it still wouldn't hurt to have it angled up slightly since the lighting is coming from slightly above--in the normal case, at least. Both the scripts and the DNG Profile Editor can handle a non-rectangular shape so having the camera perpendicular is not necessary.
> I don't know if your saturation-error experience is different than mine or not, except to say that if your numbers are ending up at -100 or +100 then something is wrong. It probably depends, somewhat, on the particular camera. the particular color of light, the age and condition of the color-checker you're using, and the emphasis Adobe chose to put on various aspects of the color-profile you are calibrating against. If you have used LR 2 or ACR 4.6+ with the Adobe's camera-matching profiles (now just released from being non-beta) then you will see how much variation there is between different ones that try to emphasis certain colors, either to make them more saturated or to make them more accurate. I have my default calibration in Lightroom and ACR set to a dual-color custom profile that I've named 2700K-6500K (for obviously reasons) but sometimes I switch to one of the camera-matching profiles: Neutral or Landscape or Portrait, depending on which I like the best for the colors in the shot. The Landscape profile typically emphases certain colors that make outdoor shots without people look more like the bright colors of a picture-postcard postcard but would make people look much too colorful so I don't use it with indoor shots or portraits, usually.
> As far as measuring the accuracy of the calibration, the numbers you get out of the scripts as their running are for just the patches being compared, which for Tom and Rags are only three, and not the whole chart, but I think Rags has a script that looks at all the colors and gives some overall number and perhaps per-patch numbers, although I'm not exactly sure.
> I use the less-expensive (but still not cheap) version of Imatest for gauging color accuracy of my calibrations or profiles. It gives several overall numbers representing color-error measured in several different ways, plus it
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