Color space - please confirm I have this correct

[Linwood Ferguson]

This is the HDR workflow I have been using, and would appreciate confirmation I am understanding it properly (or correction of course): 

1) Use Photoshop to merge HDR bracket sets (let's say there are 18 sets of 3 (+1, 0, -1).

1a) The ACR defaults to 16 bit ProPhoto RGB color (that's a statement, I have it set that way).

1b) The Merge is with the automated merge to HDR pro.

2) Save each of these as a 32 bit HDR file (here I mean the HDR file type, I think called Radiance).

3) Stitch and produce a panorama, and output as HDR file type (Radiance) again.

4) Load the HDR into Photoshop, tell it to ASSIGN the ProPhoto RGB color.

5) Edit as needed and convert to 16 bit and tone map

6) Save-as TIF for future edits (this will be ProPhoto RGB).

7) CONVERT to sRGB 

8) Save as JPG for input into the pano viewer, which will properly be in sRGB.

Does this sound right? 

And if I were to output a 16 bit TIF or 8 bit JPG file from PTgui in step (3), I assume it has no profile but the color space used is still ProPhoto RGB (there's no control over that, it just spits out what you put in)? 

I am struggling a bit with the tone mapping in step (5) to get the look I want; I think I have the right color space, but I want to make sure I am not misunderstanding the 16/32/stitch process' preservation of ProPhoto RGB.

PS. The reason I am merging outside of PTgui is that I get lots of ghosting artifacts, e.g. blowing branches or flags, if I let PTgui do the merge; am I missing a deghost option?  Plus I think it is more efficient - Photoshop does a fine job of aligning and converting to HDR format, all purely automatically, and I need only deal with 1/3 or 1/5 as many files in PTgui, albeit larger ones.

[PTGui Support]

Hi Linwood,

Your assumptions are correct. The stitching in PTGui does not affect the
color space, but PTGui currently cannot read/write color profiles in
.exr or .hdr images. You just need to tag the resulting panorama with
the correct color space afterwards, no conversion is needed.

Tone mapping will completely mess up the color profile: the pixel values
in the tone mapped images are no longer related to the actual scene
luminance. Chromacities are not affected though. So your tone mapped
image will have ProPhoto RGB chromacities but with unknown curves.

Currently there's no deghosting option in PTGui for HDR, moving objects
will indeed cause problems.

Kind regards,

New House Internet Services BV
Joost Nieuwenhuijse

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PTGui - Photo Stitching Software

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For support see: http://www.ptgui.com/faq/
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[Linwood Ferguson]

Thank you, Joost. 

As to "Tone mapping will completely mess up the color profile"... 

Would you then suggest converting to sRGB before the merge to 32 bits?    Or any other change to this flow that will make for more natural colors? 

I am very much after photo-realistic, and not the artificial glow and unrealistic saturation that some HDR photographers prefer, I use HDR here only to penetrate further into shadows and kill some of the highlights for outdoor scenes.

I was afraid to merge HDR brackets to a 16 bit TIF as I thought that would be the equivalent of doing auto-exposure, which is generally not recommended.

Thanks, Linwood.

[PTGui Support]

'mess up' I meant just from a theoretical viewpoint :-)

A color profile is meant to define the relationship between real world
luminances and pixel values. Tone mapping attempts to compress a wide
dynamic range into a narrow dynamic range while preserving local
contrast, and by doing this there is no longer a 1-to-1 mapping of
luminance to pixel brightness.

But in any case the tone mapper in PTGui was designed to give pleasing
results at a gamma of 2.2 (like sRGB). ProPhoto has a gamma of 1.8 so
the result might look too contrasty. But you compensate by adjusting the
contrast in the tone map settings. Keep in mind that PTGui is not aware
of color profiles, so the colors in the GUI will look wrong.

Also if the end result is an sRGB image you could as well convert to
sRGB early in the process, I don't think you would loose any image quality.

Kind regards,

New House Internet Services BV
Joost Nieuwenhuijse

-----------------------------------------------
PTGui - Photo Stitching Software

www.ptgui.com
For support see: http://www.ptgui.com/faq/
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[Keith]

Hi Linwood.

You're workflow seems very complicated!! I can't really follow what you are doing, but I'll try to help ... :-) Here is what I'm currently doing:

1: HDR means shooting at least 5 shots with 2ev gaps. 3 with 1 ev gaps as you seem to be doing isn't HDR I'm afraid. My current camera has a handy 7 shot HDR mode so I'm now shooting 7 with 2ev gaps, overkill, but it's automatic. I shoot raw too. 6 in a circle, one up, one straight down and one to the side for the nadir patch. That's up to around 9x7=63 raw files per panorama.

2: Drop the raw files, untouched, into PTGui. I have to use the perspective correction for the sideways nadir, involves setting a few control points, 4 is usually enough. But most of the stitching is largely automatic these days. PTGui outputs an equirectangular image, 2x1 ratio, 32bit HDR .exr file. Mine are currently coming out around 12600 pixels wide.

3. Tone Map this in Photomatix, do all the colour correction, sharpening, creative bit, etc, here (no need for Photoshop). Output a 16bit Tif. My monitor is colour calibrated with a Spyder5 Elite.

4. Use this Tif file directly in Pano2VR to produce the web ready output. It takes care automatically of the downsizing, etc. Pano2VR has a great patching tool if I need correct any blemishes. An optional extra is it can patch these back to the original tiff (or even .exr if you want to) as well. But that's only necessary if you need a perfect 2x1 file for regular printing.

5,. Job done. 

A few days ago I shot 5 panoramas around Caernarfon Castle near my home. The shoot took around 30 minutes. I think I had nearly 600 images in the camera. It took about 90 minutes to process all these and the tour was on-line. Here's a link to it: http://www.fachwen.org/urban/

On the same website I've written a little piece on my workflow with a few more details and background, constantly updated as things improve!!: http://www.fachwen.org/about-me/workflow/

Hope that helps and you start getting some good results.

Regards,

Keith

[Linwood Ferguson]

What I am doing may be more complex than needed (which is why I posted it), but doing the HDR stack alignment inside PTgui (which I think you are suggesting) does not work well for me due to ghosting.  For interior shots that may be a good option, but the examples I was using are outdoors, a soccer stadium and a softball stadium.  Flapping palm trees and flags and the like just did not work correctly when aligned in PTgui.  I've tried it a few times, and did not like the results as well as if I merged the stacks in Photoshop first.

Am I missing something in PTgui's use/   Is motion in a stack not an issue?

As to dropping the untouched NEF's in PTgui, I have tried that, but I was not as happy with the color rendition for LDR images as with Lightroom.  I use a custom camera profile, and apply a bit of post processing first.  That's LDR. 

For HDR, if I did that, PTgui uses a converter (cdraw I think) under the covers.  How does that process handle color spaces?   (And does it matter?)   Again, that's why I asked.  How color spaces interact with a 32 bit merge and then tone mapping back to 16 bit is a but of a mystery to me (maybe to be more precise, what I am saying is "what is the preferred way to do that").  I do know one way to really trash a photo is assign the wrong color profile to it.

As to using 1 stop HDR I probably should not even mention that aspect.  This is all experimentation at this point, to understand how things work.  In most cases I did not even need HDR, but wanted to have a stack so I could see how it came out.  I am limited, the older Nikon cameras only do 1 stop brackets (I think I can do either 7 or 9 in a bracket though).  Hence the 1 stop. The use of 3 was just to get something to experiment with.  If I really needed HDR for a shot, I agree I would use more images.  I guess that "isn't HDR" depends on ones definition -- to me at this point HDR means brackets to align, convert to 32 bit and tone map.  I am working on understanding the process moreso than the end result at present.  But I do understand your point that +/- 1 is not really enough to provide an HDR effect of any substance.

[Erik Krause]

Am 12.12.2015 um 09:36 schrieb Keith:

> 2: Drop the raw files, untouched, into PTGui.

I'd never use raw directly in PTGui. There is no point, since you loose
almost all benefits of shooting raw - especially there is no CA
correction, no highlight restoration (might be not necessary in your
case), no raw de-noising or sharpening etc. PTGui uses dcraw internally,
which does a pretty poor raw conversion compared with dedicated programs.

You might get better results using jpeg straight from the camera, since
the tonal richness is provided by the bracketed images anyway.

--
Erik Krause
http://www.erik-krause.de

[jstu...@goldeneraproductions.org]

Linwood, On the subject of Nikon's ability (or disability) to produce anything beyond 1-stop exposures in a bracket sequence, I use a piece of software called DSLR Remote Pro made by Breeze Systems.  It will run your camera over USB, exposing up to 15 exposures as many stops apart as you want, it downloads images directly to your pc/laptop via USB, it ensures hands-free operation (shutter release is activated by pressing F8 on your keyboard) and all around it makes things quite easy when shooting HDRs.  I believe they make a version for Nikon (I currently am using a Canon although I'd prefer a Nikon to be honest).

If you want to break out of the 1-stop only problem, this is your ticket. It's also fairly cheap.

Jon S

[Erik Krause]

Am 13.12.2015 um 04:40 schrieb jstu...@goldeneraproductions.org:
> I use a piece of software called DSLR Remote Pro made by Breeze

> Systems. [...] (I currently am using a Canon although I'd prefer a
> Nikon to be honest).

I won't spend any money for extended bracketing if there is a free
alternative (for Canon DSLR): magic lantern (which actually can do much,
much more).

For other solutions see
http://wiki.panotools.org/Extended_bracketing_control

[Linwood Ferguson]

Thanks, Erik, for me though it's just a solution in search of a problem.  I can do 9 shots covering 9 stops, which is pretty broad, and if I don't want the intermediate stops just delete those once I download.  Deleting a burst with one button, even if I need to delete some later, is a lot easier than carrying around a tablet or laptop and hooking it up in the field. 

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