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bullfrog
02-22-2012, 09:08 AM
I know what you guys are thinking :

":wip: DAMN THERE ARE PLENTY OF TUTORIALS ALL OVER THE WEB, READ THEM BEFORE POSTING !!! :wip: "

I read them all ! But tutorials are always about how to make LWF inside the 3D application.
What I want to know (and I'm sure I'm not the only one) is how to handle in post with PHOTOSHOP.

We know photoshop doesn't handle 32 bits properly. so my thread is all about dealing with that.

My reference is the image I have in the Vray frame buffer with srgb checked. (gamma 2.2, don't affect color, input 2.2, ouput 1.0, bla bla bla....)

My guess is we have to have the same look as the image reference inside photoshop. Right?

When I save in TGA no matter what I choose in bpc, it says me it is 8 bis inside photoshop. Wierd...

When I save in Tiff 16 bit I have to add a gamma correction but I don't match the image reference exactly.

When I save in Tiff 32, it looks just wrong.

The ONLY way to match is to save in 32bit EXR and when I load inside photoshop it tells me assign profile:SRGB (DNW it does that for me) and from then it looks ok. I switch to 16 bits ( like TGA whatever I choose in max, it save my EXRfiles in 32 bits) and I can start tweaking my image.

IS THAT CORRECT? IS THAT LWF?
:deal:

bullfrog
03-01-2012, 03:19 PM
up? :blush:

DanGrover
03-01-2012, 03:43 PM
I never use Photoshop for 32bit work - it's like intentionally stapping land mines to your feet during a marathon to make it more exciting - but, for what it's worth, TGA only supports 8bit per channel data. When it says 24/32bit in the max options, it's referring to the image in total - either RGB or RGBA @ 8bpc. In the Tif window (and EXR), the bit count is referring to per channel, not the image in total. Confusing fun all round.

bullfrog
03-02-2012, 08:59 AM
Yes I know photoshop doesn't handle correctly 32 bits files format. it's why I'm working in 16 bits.

My question was more "Is my workflow linear?"

Thanks for the Tiff and TGA explanation anyways. Useful.

InfernalDarkness
03-02-2012, 11:01 PM
I've been dealing a lot with this topic myself, as I don't have Nuke or any of the big, expensive programs people use to deal with LWF. There will come a time when LWF will cease to exist, and it'll all be handled automagically inside our programs, but until then...

The .exr file is useless in Photoshop for the most part. Even with ProEXR you get poor control and results. I've not had any success in using it, good thing it was so cheap at least!

I've been using .tiff files, 32-bit float and so far this is about the best way to go. Granted, you can't store passes in them directly, but that's not a huge deal unless you're animating, which I'm not. I've had success with 16-bit half files as well, however.

Quick example from a current personal project:

http://img441.imageshack.us/img441/4106/forestpathmr27tiffweb.jpg

This is the raw .tiff, simply converted to a .jpg. And here it is after a little work:

http://img546.imageshack.us/img546/5717/forestpathmr27web.jpg

The main trick for me is to output a decent, usable z-depth pass, which is a pain in Maya, but works pretty well. But back to the topic:

Is this image linearly correct?

gerardo
03-13-2012, 10:25 PM
We know photoshop doesn't handle 32 bits properly. so my thread is all about dealing with that.
Well, many filters don't work at 32-bpc in PS. There's also a misunderstanding about how the alpha channel (in the transparency sense) is used in EXR workflows by the CG/VFX industry. Fortunately, ProEXR solves the EXR issue.

My reference is the image I have in the Vray frame buffer with srgb checked. (gamma 2.2, don't affect color, input 2.2, ouput 1.0, bla bla bla....)

My guess is we have to have the same look as the image reference inside photoshop. Right?
Have no idea if/how Vray manages color profiles, but ideally, yes. Though this is not always the case - mostly if formats, standards or color engines are different. But let's suppose this is the case.

When I save in TGA no matter what I choose in bpc, it says me it is 8 bis inside photoshop. Wierd...
Tga is 8-bits per channel (RGBA = 8-bits R + 8-bits G + 8-bits B + 8-bits A = 32 bits - but not per channel!). The correct term would be n-bpc, not just n-bits...

When I save in Tiff 16 bit I have to add a gamma correction but I don't match the image reference exactly.
16-bpc formats are not considered full floating point (FP), and it's assumed that their data have been stored non-linearly, then no LUT (display gamma correction) will be applied by PS. If you apply a simple gamma correction (Levels filter), you won't match your image reference exactly, because the 2.2 gamma exponent is similar - but not the same - as the sRGB formula. There are several ways to solve this, but guess the simpler one is just saving (from your render package) the 16-bpc images with the sRGB profile tagged in the output settings. We save with gamma 1.0 only when the output format is full FP (32-bpc).

When I save in Tiff 32, it looks just wrong.
Guess what is happening there is that this Tiff 32 is 8-bpc. If so, you should be seeing posterizations in the dark areas of your image after gamma correction due to quantizations. It's not efficient storing linear data in 8-bpc files because there's not much bits to store the data where human vision is more sensitive (dark areas).

The ONLY way to match is to save in 32bit EXR and when I load inside photoshop it tells me assign profile:SRGB (DNW it does that for me) and from then it looks ok. I switch to 16 bits ( like TGA whatever I choose in max, it save my EXRfiles in 32 bits) and I can start tweaking my image.
There are some things happening behind the scenes there. When you load a 32-bpc image, PS will assign - on the fly - a linear version of the working color space that it's using. Then, it applies a LUT to show you the image accordingly with the non-linear version of the working color space. Then, when you switch to 16-bits (and don't change anything in the conversion panel), PS automatically will convert from the linear version of the working color space to the non-linear version, and it will disable the LUT. This operation is not noticed because we are always seeing a gamma corrected image.

IS THAT CORRECT? IS THAT LWF?
Nope. As we have seen, you are working in 16-bits with the non-linear version of the working color space. In order to work in linear light you need force a linear space in 16-bits.

To do so you can create a linear profile of your working color space. There are several ways to do this, but the simpler one is probably within PS.

Go to Edit=>Color Settings and in Working Spaces (RGB), choose the color space you want to linearize from the color spaces list:

http://imagic.ddgenvivo.tv/forums/SGCCTools/linPS1.png http://s16.postimage.org/4gp5daarp/lin_PS1.png

Then, in the same list (in the top of the list) select Custom RGB...

http://s14.postimage.org/h4kzjw6i9/lin_PS2.png

http://imagic.ddgenvivo.tv/forums/SGCCTools/linPS2.png%20 A window will pop up with some settings to adjust for a given color space:

http://imagic.ddgenvivo.tv/forums/SGCCTools/linPS3.png http://s17.postimage.org/iknbanhun/lin_PS3.png

Change the name of the color space to something like Linear_sRGB or any other color space you have chosen and change the gamma value to 1.0 (the gamma value that we see there for some color spaces are only approximations).

We have there also different white points settings and their description in xy coordinates. We have also the primaries described in some color models. But you'll be ok if you leave this part as it is.

Then, in the same list, below Custom RGB, you'll find an option to save the color profile called Save RGB:

http://imagic.ddgenvivo.tv/forums/SGCCTools/linPS4.png http://s14.postimage.org/oacqmcfld/lin_PS4.png

Choose Adobe Profiles folder and now you'll see the lin version of your profile listed in the working color spaces list.

You can then convert to this linear profile when working with 16-bits images.

Idea is that when you set the working color space, let's say sRGB and open the EXR image (without alpha), the color appearance should be sRGB - but remember, PS is using a linear version of your working color space and applying a LUT on the fly. So when you switch to 16-bits (no exposure and gamma adjustments), your working color space is non-linear. Then, in order to work in linear space, you can convert (Asolute Colorimetric) from the non-linear profile of your working color space to the linear version that you have previously created. That's all.

You won't see any difference because when we work with a linear profile, PS applies a LUT to properly display the images. But if lets say, you apply a lens blur, you'll notice the difference in the bokeh effects and such.

Later for saving, convert back to the non-linear profile.

Guess there are several ways to solve this, but if you ask me, and barely you have the chance, try to switch to a compositing package instead. i.e. you might use After Effects for all the RGB work. Its linear workflow is the most automatic thing and the most (if not more) of the filters/FX available in PS are also available (or substitutable) in AFX. Later you could switch to PS or Lightroom for the CMYK phase.



Gerardo

P.D. Photoshop alpha issue with OpenEXR images has finally been solved with the new OpenERX Alpha plug-in (http://helpx.adobe.com/photoshop/kb/install-openexr-alpha-plug-photoshop.html).

bullfrog
03-14-2012, 12:23 PM
thaaaaaaaaaaaaaaaaaaaaaaaank youuuuuuuuuuuuuuuuuuuuuuuuuuu!

Jozvex
03-16-2012, 04:35 AM
Photoshop really needs proper EXR support. I use EXR '16bit [half]' format (half precision floating point) for almost everything these days and I think Photoshop loads them as 32bit. I don't have ProEXR though as I mainly use Fusion for compositing. So many hurdles we still need to overcome!

InfernalDarkness
03-16-2012, 05:07 AM
Yeah, if you don't have ProEXR running, it's almost pointless to use .exr files in Photoshop. Even then, it's very basic and unforgiving. I do like Nuke as a program, but should we really need Nuke just to use a particular file type? How is the data in an .exr so difficult for Adobe to deal with?

CHRiTTeR
03-16-2012, 02:13 PM
*nevermind

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