How can I make extreme perspective corrections?
Gareth
Here is a question you may like to consider, especially if you have
been kind enough to look at the previous thread.
I have been making panoramas of flat paintings. I like to take the
original photographs slightly to one side of the painting (for reasons
discussed in the previous thread).
This means the painting appears quite distorted at first.
I am used to using left-click and drag to adjust location, and right-
click and drag to adjust rotation, but in these recent panoramas the
corrections needed have been so extreme I find those tools becoming
more difficult to use.
For example, when I have corrected vertical convergence, and almost
finished correcting horizontal convergence, the painting no longer
appears to be vertical. I then try to rotate but, because the centre
of rotation is now a long way from the painting, rotating seems to
shift the convergences as well as rotating the painting.
http://groups.google.com/group/ptgui/web/How%20can%20I%20correct%20extreme%20perspective.jpg
I know I could easily make this sort of correction by using the warp
tool in an image editing programme such as Picture Window Pro, but I
would prefer to get as correct as possible in PTGui Pro to begin with.
Can anyone suggest a more systematic approach than the trial and error
I am using at present?
Gareth
ozbigben
If you're photographing it at an angle, then it shouldn't appear in
the centre of the panorama. Get the vertical sides straightened and
then adjust the yaw of the entire panorama in the opposite direction
to which you photographed it. You'll end up with a larger image with
the painting on one side, then just crop the final output.
You could try specifying control points for the horizontal edges and
just optimise yaw angles, or just put a grid on the visual editor and
move it manually.
Ben
On May 3, 6:03 am, Gareth <gar...@garethhawker.freeserve.co.uk> wrote:
> Hi Everyone,
>
> Here is a question you may like to consider, especially if you have
> been kind enough to look at the previous thread.
>
> I have been making panoramas of flat paintings. I like to take the
> original photographs slightly to one side of the painting (for reasons
> discussed in the previous thread).
>
> This means the painting appears quite distorted at first.
>
> I am used to using left-click and drag to adjust location, and right-
> click and drag to adjust rotation, but in these recent panoramas the
> corrections needed have been so extreme I find those tools becoming
> more difficult to use.
>
> For example, when I have corrected vertical convergence, and almost
> finished correcting horizontal convergence, the painting no longer
> appears to be vertical. I then try to rotate but, because the centre
> of rotation is now a long way from the painting, rotating seems to
> shift the convergences as well as rotating the painting.
>
Gareth
Thanks for your reply!
As far as I can understand you have described exactly what I am doing
already. I attempted to show this in the picture file I posted.
My question was, is there an easier, more systematic, way of doing
this. At present I am just moving the image around the screen as you
descibe, and eventually getting the right result by trial and error
with reference to the grid.
One thing you mentioned I had not thought about - optimising yaw
angles. But I believe they were already optimised when the panorama
was being constructed?
Anyway thanks for having given this some thought.
Regards,
Gareth
Gareth
> One thing you mentioned I had not thought about - optimising yaw
> angles.
suggest.
http://hugin.sourceforge.net/tutorials/perspective/en.shtml
Unfortunatly I could not get it to work in PTGui. It just casued the
painting extend outwards like a magic carpet! Pehaps this sort of
correction cannot be made at the same time as Viewpoint correction?
Regards,
Gareth
Erik Krause
>
> I found this page, which describes using control points as you
> suggest.
>
> http://hugin.sourceforge.net/tutorials/perspective/en.shtml
>
> Unfortunatly I could not get it to work in PTGui.
See here: http://wiki.panotools.org/Perspective_correction
> It just casued the
> painting extend outwards like a magic carpet!
This is quite normal. You must extend the Output field of view in order
to get the corrected version. Once you see it completely in the pano
editor you can use the yellow lines to crop to the final size.
> Perhaps this sort of
> correction cannot be made at the same time as Viewpoint correction?
Depends ;-) Viewpoint correction does more or less the same but works on
input images whereas perspective correction works on output images.
Hence if you have only one input image do either one or the other but
not both. If you want to correct a whole panorama, stitch it first
uncorrected for best fit (using viewpoint correction on some images
would be no issue). Once it is ready you can do a perspective correction
using control points like described in the wiki article.
--
Erik Krause
http://www.erik-krause.de
Gareth
Thanks for the suggestions.
> If you want to correct a whole panorama, stitch it first
> uncorrected for best fit (using viewpoint correction on some images
> would be no issue).
> Once it is ready you can do a perspective correction
> using control points like described in the wiki article.
optimiser a second time (this is what does not seem to work for me),
or do you mean first render the panorama as a .tif, then proceed to
correct the perspective?
Regards,
Gareth
Erik Krause
> > Once it is ready you can do a perspective correction
> > using control points like described in the wiki article.
>
> Do you mean add vertical and horizontal control points and click on
> optimiser a second time (this is what does not seem to work for me),
This should produce the identical result like the workflow you describe
below. However, I don't know how viewpoint optimization exactly works
and whether it depends on output parameters (it should not in my
opinion). Hence it might be a good idea to disable viewpoint
optimization for the perspective correction step. This doesn't delete
the actual viewpoint correction values as you can see on Image
Parameters tab.
> or do you mean first render the panorama as a .tif, then proceed to
> correct the perspective?
This would be another way and should work as well. But it takes
additional time, disk space and another interpolation step, hence I
would try to avoid it. PTGui should be able to do anything in a single step.
Gareth
> optimization for the perspective correction step. This doesn't delete
> the actual viewpoint correction values as you can see on Image
> Parameters tab.
I tried it out and it did seem to make a difference, but I still did
not end up with a rectangle. However the result was closer to a
parallelogram than before.
Regards,
Gareth
Erik Krause
> I tried it out and it did seem to make a difference, but I still did
> not end up with a rectangle.
If you perspective correct a rectangular image it never stays
rectangular (in rectilinear output projection). If it is corrected
vertical or horizontal only it is distorted to a trapezium. If corrected
diagonally it gets an irregular four-sided shape.
The correction parameters for the tight spaces example on
http://wiki.panotools.org/Perspective_correction#Camera_tilted_and_rotated
are Yaw=-23.5 Pitch=58.8 and Roll=-13. You can enter them manually in
Image Parameters tab to get the corrected version. On Panorama Settings
tab set Field of View to at least 145°x160° to see the complete shape in
Panorama Editor.
Gareth
> rectangular (in rectilinear output projection). If it is corrected
> vertical or horizontal only it is distorted to a trapezium. If corrected
> diagonally it gets an irregular four-sided shape.
I started with may be rectangular (actually it is not exactly so
because I aim the camera irregularly when capturing the source images)
but the part I am interested in, the painting, is not rectangular as
it appears in the panorama.
My intention is to end up with the painting as a perfect rectangle. I
do understand this means the entire image (including the background
outside the frame around the painting), will become an irregular four-
sided shape – very ragged-edged in my case
The man in the example you quote has done exactly what I want. He has
photographed a rectangular subject which has turned out as an
irregular four-sided shape. He has then distorted this image to ensure
the subject becomes a rectangle. I can do this easily in an image-
editing programme, but not, so far, in PTGui. I guess I must be
missing something - I just cannot track down what I am doing wrong.
Regards,
Gareth
ozbigben
added in to the workflow.
1: Make your output image much wider than your painting, and
rectilinear. If your camera is tilted at 15° to the painting then you
will need at least an extra 30° (2x15)
2: Optimise your project without perspective correction. Include
vertical lines and horizontal lines for the edges of the frame.
Here's an old sample from my archives (reworking the site at the
moment)
http://archive.bigben.id.au/tutorials/360/alternatives/tight_spaces.html
Your image should be off to one side (hence the need for the extra
width)
3: Then experiment with turning off yaw/pitch/roll optimisation of all
images and adding perspective optimisation of all but one image.
(I haven't tested this yet, but it sounds like it's worth a try)
Ben
ozbigben
and then optimise the viewpoint of ALL image tiles. You may only need
control points between tiles and the 4 corners, although some extra
points may be useful for statistical accuracy. try selecting a grid of
control points across the painting (between the tile images and the
reference image)
Ben
Gareth
I don't understand. Aren't you describing exactly what I showed in my
first post?
http://ptgui.googlegroups.com/web/How%20can%20I%20correct%20extreme%20perspective.jpg
The image in the middle is the panorama as it came out of PTGui in the
first instance, and the image at the bottom right is the same panorama
after I had shifted it across the screen of the Panorama Editor.
Regards,
Gareth
On May 3, 11:30 pm, ozbigben <ozbig...@gmail.com> wrote:
> Haven't tried it with perspective correction yet, but it could be
> added in to the workflow.
>
> 1: Make your output image much wider than your painting, and
> rectilinear. If your camera is tilted at 15° to the painting then you
> will need at least an extra 30° (2x15)
> 2: Optimise your project without perspective correction. Include
> vertical lines and horizontal lines for the edges of the frame.
>
> Here's an old sample from my archives (reworking the site at the
Gareth
it.
If I understand you correctly, the reference image, taken with the
camera perpendicular to the painting, would include the entire
painting.
Are you suggesting I include this as one of the source images in a
panorama project made up of, say, 100 source images of tiny parts of
the painting (all taken with the camera in different positions
relative to the painting). Is this what you mean?
I understood that all images in a PTGui project had to be the same
size. Please correct me if I am wrong.
Regards,
Gareth
John Houghton
wrote:
>
> I understood that all images in a PTGui project had to be the same
> size. Please correct me if I am wrong.
different lenses (and in different orientations, if you wish). You
need to assign individual lens parameters via the Lens Settings tab
(Advanced mode). The many small images would share the same global
parameters, as usual, and the reference image would have its own
individual parameters, which can be entered on the Image Parameters
tab. Extra check boxes will appear on the Optimizer tab (Advanced
mode) to enable them to be optimized if required.
Another example of this type of stitching is described in this
tutorial, in which a fisheye camera shot of the heavens is aligned
with a reference equirectangular image (a star map). The star map is
assigned fixed individual lens parameters. By setting control points
between stars in the camera shot and the reference map, the lens
parameters can be accurately evaluated by the optimizer.
http://www.johnhpanos.com/starcal.htm
John
Gareth
> and whether it depends on output parameters (it should not in my
> opinion).
Houghton's tutorial, on straightening a panorama, these dread words,
"The PTGui optimizer does not support t1,t2,tn points, so you must
select the Panorama Tools optimizer"
When I do this a message warns me. "Your project uses viewpoint
correction, but this is not supported by the Panorama Tools optimizer.
Please choose 'Optimize using PTGui' instead."
> Hence it might be a good idea to disable viewpoint
> optimization for the perspective correction step. This doesn't delete
> the actual viewpoint correction values as you can see on Image
> Parameters tab.
Viewpoint boxes, but got the same message. I also tried optimizing a
second time with PTGui tools and the Viewpoint boxes delselected, then
tried Pano tools again, but with the same result.
> PTGui should be able to do anything in a single step.
Regards,
Gareth
> --
> Erik Krausehttp://www.erik-krause.de
michael crane
tried Pano tools again, but with the same result.
>
>> PTGui should be able to do anything in a single step.
it's a giant step for software
mick
John Houghton
> Maybe this is where I have been tripping up. I noticed in John
> Houghton's tutorial, on straightening a panorama, these dread words,
> "The PTGui optimizer does not support t1,t2,tn points, so you must
> select the Panorama Tools optimizer"
points, but not tn points. There is a link to a more up-to-date
tutorial right at the beginning. (The link was broken due to a move
to a new server but is now corrected).
John
Ken Warner
michael crane
>
> I use tn points in PTGui 8.4.1...
mick
Bjørn K Nilssen
>
> I use tn points in PTGui 8.4.1...
How do you know they are working?
One problem with the PTgui lines is that you get no feedback/errors, like with the
panotools lines. So you never know if it really worked?
--
Bjørn K Nilssen - http://bknilssen.no - panoramas and 3D
John Houghton
optimizer does not support them. Even the t1 and t2 points are not
supported in the same way as they are in Panorama Tools. In PTGui's
optimizer, the t1 and t2 points are processed in relation to the
entire aligned panorama image. The image is merely transformed as in
the numerical transform option, and the way the images align with each
other is not affected. They cannot be used to help in the evaluation
of lens parameters to correct barrel distortion, say. (It's the same
levelling operation that's available as Level Panorama in the Edit
menu of the Panorama Editor window).
In Panorama Tools, the t1,t2 and tn points are processed along with
all the normal (t0) points and can directly affect the warping of the
individual images and how they align with each other. Multilple
t3,t4,..,tn points are assigned along the length of straight line
features (t3 points on line 3, t4 points on line 4 etc.). PTOptimizer
will try to get the points on each line into a straight line.
John
michael crane
>
> On May 4, 5:13 pm, Ken Warner <kwarner...@verizon.net> wrote:
>> I use tn points in PTGui 8.4.1...
>>
> PTGui will enable you to create t3,t4 ...,tn points but its own
> optimizer does not support them. Even the t1 and t2 points are not
> supported in the same way as they are in Panorama Tools. In PTGui's
> optimizer, the t1 and t2 points are processed in relation to the
> entire aligned panorama image.
yes ok guys ! what are the t1,t2,t3 etc ?
mick
Erik Krause
> > However, I don't know how viewpoint optimization exactly works
> > and whether it depends on output parameters (it should not in my
> > opinion).
>
> Maybe this is where I have been tripping up. I noticed in John
> Houghton's tutorial, on straightening a panorama, these dread words,
> "The PTGui optimizer does not support t1,t2,tn points, so you must
> select the Panorama Tools optimizer"
Well, that was true when the tutorial was written, but is not true for
the most recent versions. PTGui now supports t1 and t2 (vertical and
horizontal) line control points. It handles them a bit different than
the panotools optimizer but the result should be the same.
> When I do this a message warns me. "Your project uses viewpoint
> correction, but this is not supported by the Panorama Tools optimizer.
> Please choose 'Optimize using PTGui' instead."
>
> > Hence it might be a good idea to disable viewpoint
> > optimization for the perspective correction step. This doesn't delete
> > the actual viewpoint correction values as you can see on Image
> > Parameters tab.
>
> I tried to disable viewpont optimization by deselecting all the
> Viewpoint boxes, but got the same message. I also tried optimizing a
> second time with PTGui tools and the Viewpoint boxes delselected, then
> tried Pano tools again, but with the same result.
That is because PTGui keeps the viewpoint correction values. If you want
to use panotools optimizer you must zero all five VP columns on Image
Parameters tab (Click column header to select all fields, type 0 and
press enter.)
> > PTGui should be able to do anything in a single step.
>
> Perhaps not yet?
Could you provide a zip with small version of your images somewhere
alongside with the project file? It would be much easier to help...
best regards
Erik Krause
> I use tn points in PTGui 8.4.1...
Well, no wonders. You are ahead of time. Must have been version 8.2 or
8.3 when Joost will have had implemented that. ;-)
However, current version 8.1 doesn't process them...
Ken Warner
hummmm.... to tell the truth, when I used them, I couldn't
see the difference in the alignment. Oh well.
So before I lift a finger to look for the tutorial on how
to use PTOptimiser :-) is there a tutorial on how to use
PTOptimiser in PTGui???
michael crane
>
> So I was creating tn points but they are ignored in PTGui?
:-)
mick
Ken Warner
machine but I'm not supposed to tell... :-)
Ken Warner
since I barely understand them but this might help.
http://www.photoactivity.com/Pagine/Articoli/017%20Stitch%20approfondimento/PTgui%20advanced%20techniques.asp
John Houghton
>
> <scream> what are tn points </scream>
>
features (t3 points on line 3, t4 points on line 4 etc.). PTOptimizer
will try to get the points on each line into a straight line".
because of barrel distortion in the original camera image. By
assigning a row of t3 points along the feature, PTOptimiser can vary
the lens parameters (notably "b") to correct this by getting the
points into a straight line. Several lines can be marked in this way,
each with a different line type (line 3, line 4, line 5,... etc).
This assumes that each line should be correctly rendered straight in
the chosen output projection - such as a vertical in a cyclindrical or
equirectangular image, or the natural horizon. All straight lines are
preserved in a rectilinear projection.
John
michael crane
I'm not adverse to a bit of maths but sometimes this looks like gobbledegook
somebody ( I nominate Eric :-) ) should explain all this stuff for
dumb photographers.
mick
John Houghton
> I'm not adverse to a bit of maths but sometimes this looks like gobbledegook
> somebody ( I nominate Eric :-) ) should explain all this stuff for
> dumb photographers.
http://www.erik-krause.de/index.htm?./verzeichnung/distort_en.htm
John
Erik Krause
> <scream> what are tn points </scream>
For n>2 look here:
http://wiki.panotools.org/Straight_line_control_points
For t1 and t2:
http://wiki.panotools.org/Horizontal_control_points
http://wiki.panotools.org/Vertical_control_points
Gareth
> Could you provide a zip with small version of your images somewhere
> alongside with the project file? It would be much easier to help...
to make a zip file.
The pictures are very small but I think large enough to show roughly
what I mean. They join together fairly well with automatically
generated control points.
For the purposes of this discussion I do not believe it is worth
spending time adding points manually, although I have done so with the
original images. The edges of the painting then do end up completely
straight, not barrel-distorted as they appear when only automatically
generated control points are used.
http://groups.google.com/group/ptgui/web/Gareth%20Hawker%20-%20Pastel%20test%2001.zip
Regards,
Gareth
Erik Krause
> So before I lift a finger to look for the tutorial on how
> to use PTOptimiser :-) is there a tutorial on how to use
> PTOptimiser in PTGui???
If you have panotools installed (look in Tools->Options->Panorama tools)
you simply select "Optimize using: Panorama Tools optimizer" on the
Optimizer tab. That's all.
PTGui will complain if you used viewpoint correction on some of the
loaded images before or if you have viewpoint correction checked. In
this case uncheck viewpoint correction for all images and zero all VP
values on Image Parameters tab (or start over with a new project).
Rouse
Sent from my iPhone
On May 4, 2009, at 2:58 PM, Gareth
Gareth
> You can have a mixture of images taken with
> different lenses (and in different orientations, if you wish).
been quite a revelation. I do not know why I supposed all images had
to be the same size. Maybe once I tried to combine areas of a partial
panorama separately, saved as tifs, then found I could not join the
separate areas in PTGui.
>...By setting control points
> parameters can be accurately evaluated by the optimizer.
Regards,
Gareth
Ken Warner
I saw the option on the Optimizer tab but I thought
there must be something else to do. It just looked
too simple.
I don't have PTGui Pro so I guess I just select PTOptimizer
and go. The reason I haven't used it before is because
I didn't know PTGui didn't service tn points.
I learned something today. These mailing lists aren't all bad :-)
Ken
John Houghton
instructions in the Help pages at:
http://tinyurl.com/cbdtlp
John
>
> > Regards,
>
> > Gareth- Hide quoted text -
>
> - Show quoted text -
michael crane
> For n>2 look here:
> http://wiki.panotools.org/Straight_line_control_points
gosh I never noticed new line t3 before
regards
mick
Erik Krause
> For the purposes of this discussion I do not believe it is worth
> spending time adding points manually, although I have done so with the
> original images. The edges of the painting then do end up completely
> straight, not barrel-distorted as they appear when only automatically
> generated control points are used.
>
> http://groups.google.com/group/ptgui/web/Gareth%20Hawker%20-%20Pastel%20test%2001.zip
I must admit that I failed on these images. It seems as if PTGui isn't
able to use t1 and t2 points correctly if viewpoint correction is active
for some images. Joost, could you look into that?
However, it works perfectly if I perspective correct only one image. It
is possible to align f.e. the first image (where there are both vertical
and horizontal parts of the frame). Then fix this image and align all
others to it even using viewpoint correction.
The downside is that errors due to barrel distortion add up and the
opposite side of the frame still isn't good. Hence it would have been
interesting if you enclosed the project file where you manually set
control points on the frame. Most likely you could get a perfect result
this way if your lens was calibrated (in order to remove barrel distortion).
michael crane
>
> Can soMeone PLEASE unsubscribe me!!!
>
> Sent from my iPhone
I guess if you can't figure how to change your signature unsubscribing
must be daunting
:-)
mick
Keith Martin
Ooh, harsh. But hang on, I left that default sig on my iPhone too...
Perhaps this might help Rouse: "To unsubscribe from this group, send
email to ptgui-un...@googlegroups.com"
k
Gareth
On May 5, 9:30 pm, Erik Krause <erik.kra...@gmx.de> wrote:...
> I must admit that I failed on these images. It seems as if PTGui isn't
> able to use t1 and t2 points correctly if viewpoint correction is active
> for some images. Joost, could you look into that?
> However, it works perfectly if I perspective correct only one image. It
> is possible to align f.e. the first image (where there are both vertical
> and horizontal parts of the frame). Then fix this image and align all
> others to it even using viewpoint correction.
> The downside is that errors due to barrel distortion add up and the
> opposite side of the frame still isn't good. Hence it would have been
> interesting if you enclosed the project file where you manually set
> control points on the frame.
would still like it. The only reason I did not include it was I
believed the addresses used for each source image were specific to my
computer and so would be no use to anyone else. Is that correct?
I did not go on with that project far enough to get a perfect result -
I was only getting a rough idea of what worked. Normally I use many
more source images for a painting of this size (30 x 20 ins) so as to
achieve a high resolution output. Then it is easier to get straight
lines. I suspect the reason for this is that each image contains
sharper detail so the control point generator has an easier task.
> Most likely you could get a perfect result
> this way if your lens was calibrated (in order to remove barrel distortion).
I might get wrong. I think, for the time being, I shall stick with
making the panorama as rectangular as possible in PTGui, then transfer
to Picture Window Pro for final perspective correction.
Many thanks for having tried this out and for explaining everything to
me.
Regards,
Gareth
Erik Krause
> I should be happy to send the project file: please let me know if you
> would still like it. The only reason I did not include it was I
> believed the addresses used for each source image were specific to my
> computer and so would be no use to anyone else. Is that correct?
No. If PTGui doesn't find the path it asks for a different folder. If
you store the project file in the same location as the images, it
doesn't even contain a path.
> I did not go on with that project far enough to get a perfect result
> - I was only getting a rough idea of what worked. Normally I use
> many more source images for a painting of this size (30 x 20 ins) so
> as to achieve a high resolution output. Then it is easier to get
> straight lines. I suspect the reason for this is that each image
> contains sharper detail so the control point generator has an easier
> task.
If you do such kind of images again, simply use a tripod and if possible
a pan-tilt panoramic head. This way you won't need viewpoint correction
which would simplify the job for PTGui and allow for a good perspective
correction.
> Calibrating the lens sounds as if it might be an intensive task which
> I might get wrong.
Not at all. Simply shoot a panorama of a detailed subject (could be a
painting) from a tripod (best with pan-tilt head) using much overlap.
Let PTGui generate much control points, optimize for lens parameters and
save them to the lens database. Lens calibration is focal length
specific, hence if you use a zoom lens do it for some often used focal
lengths.
Gareth
On May 6, 7:48 pm, Erik Krause <erik.kra...@gmx.de> wrote:
> Gareth wrote:
> > I should be happy to send the project file: please let me know if you
> > would still like it. The only reason I did not include it was I
> > believed the addresses used for each source image were specific to my
> > computer and so would be no use to anyone else. Is that correct?
> No. If PTGui doesn't find the path it asks for a different folder. If
> you store the project file in the same location as the images, it
> doesn't even contain a path.
> > I did not go on with that project far enough to get a perfect result
> > - I was only getting a rough idea of what worked. Normally I use
> > many more source images for a painting of this size (30 x 20 ins) so
> > as to achieve a high resolution output. Then it is easier to get
> > straight lines. I suspect the reason for this is that each image
> > contains sharper detail so the control point generator has an easier
> > task.
>
> If you do such kind of images again, simply use a tripod and if possible
> a pan-tilt panoramic head. This way you won't need viewpoint correction
> which would simplify the job for PTGui and allow for a good perspective
> correction.
twofold: it is diffuclt to keep the central part of the painting in
focus as the same time as the outer edge of the painting. If I refocus
for the edges, that leads to incorrect stitching - thus making
viewpoint correction essential. Also it is easier to keep the lighting
even over all the painting, and to avoid glare, if each source image
is lit in exactly the same way (i.e. generally speaking, flash on
camera).
Another method is to keep the camera always perpendicular to the
painting and always the same distance. This makes stitching easy, but
it also brings problems, especially if I am photgraphing a painting
under glass hanging on a wall. Very difficult to keep the camera at
exactly the right distance and pointing in exactly the right
direction.
I may have to revert to one of these methods if I do not get on well
with viewpoint correction, though results so far have been
encouraging.
> > Calibrating the lens sounds as if it might be an intensive task which
> > I might get wrong.
>
> Not at all. Simply shoot a panorama of a detailed subject (could be a
> painting) from a tripod (best with pan-tilt head) using much overlap.
> Let PTGui generate much control points, optimize for lens parameters and
> save them to the lens database. Lens calibration is focal length
> specific, hence if you use a zoom lens do it for some often used focal
> lengths.
Regards,
Gareth
Erik Krause
> The problem is
> twofold: it is diffuclt to keep the central part of the painting in
> focus as the same time as the outer edge of the painting.
Shoot with a larger focal length from greater distance. All the
gigapixel images of large paintings on http://www.haltadefinizione.com/
where shot with a Clauss Rodeon panoramic head and very long lenses
(400mm in at least one case). On http://tinyurl.com/9dldxg you find a
video how the masterpieces in the Museo de Prado where shot in high
resolution.
> Also it is easier to keep the lighting
> even over all the painting, and to avoid glare, if each source image
> is lit in exactly the same way (i.e. generally speaking, flash on
> camera).
Use a stronger flash and point it to a wall behind, the ceiling above
or a large white cardboard or alike. Indirect flash gives a far better
lighting than direct flash, which almost ever causes unwanted reflections.
> Another method is to keep the camera always perpendicular to the
> painting and always the same distance. This makes stitching easy, but
> it also brings problems, especially if I am photgraphing a painting
> under glass hanging on a wall.
On-camera direct flash will totally Ruin your result due to reflections
in the glass. Use indirect flash or external studio flash units from the
side.
> I may have to revert to one of these methods if I do not get on well
> with viewpoint correction, though results so far have been
> encouraging.
Yes, and perhaps with a calibrated lens and the second method I
suggested it would work very good. Using an overall reference image was
discussed in another thread.
Gareth
On May 6, 9:00 pm, Erik Krause <erik.kra...@gmx.de> wrote:
> Gareth wrote:
> > The problem is
> > twofold: it is diffuclt to keep the central part of the painting in
> > focus as the same time as the outer edge of the painting.
>
> Shoot with a larger focal length from greater distance. All the
> (400mm in at least one case).
320mm equivalent on 35mm). Each source image represents about 7½ x 5
ins on the painting, overlapping by 50%.
>On http://tinyurl.com/9dldxgyou find a
> resolution.
most impressed with the enormous camera and lens, not so impressed
with the lighting, which was coming from either side. I know this is
standard copy lighting, but I think it can give a false impression of
the brush work.
> > Also it is easier to keep the lighting
> > even over all the painting, and to avoid glare, if each source image
> > is lit in exactly the same way (i.e. generally speaking, flash on
> > camera).
>
> Use a stronger flash and point it to a wall behind, the ceiling above
> or a large white cardboard or alike. Indirect flash gives a far better
> lighting than direct flash, which almost ever causes unwanted reflections.
Direct flash has been working well. (The samples I posted were taken
with direct flash on camera, and show a pastel under glass). I
sometimes use a brolly to soften the flash.
> > Another method is to keep the camera always perpendicular to the
> > painting and always the same distance. This makes stitching easy, but
> > it also brings problems, especially if I am photgraphing a painting
> > under glass hanging on a wall.
> On-camera direct flash will totally Ruin your result due to reflections
> in the glass. Use indirect flash or external studio flash units from the
> side.
> > I may have to revert to one of these methods if I do not get on well
> > with viewpoint correction, though results so far have been
> > encouraging.
>
> Yes, and perhaps with a calibrated lens and the second method I
> suggested it would work very good. Using an overall reference image was
> discussed in another thread.
forward to doing so in the future.
With thanks again.
Regards,
Gareth