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Old 12-06-2012, 06:57 PM   #1
olli20
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Oliver Schulz
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Unhappy layered exr issues

Hi there!

I got an interesting problem which I assume some of you may have run into. The problem is as follows:
I do my Mattepainting in 16 bit in PS and want to export it to Comp.To make it nice and clean I want to export a layered EXR file from Photoshop. So here comes the hazzle! To be able to export an 16 bit exr from PS I have to switch my Mode to 32 bit. And here it comes, halftransparent pixels become more opaque, which is quite a pain for stuff like fog etc..

So I got a question to you guys! How do you handle multilayered Mattepaintings pipeline wise?
Do you export each layer seperately with a seperate alpha channel as for instance a .tif file? Or is there a special trick when exporting a layered exr from PS? So nobody really seems to know what PS does exactly when converting an image from 16 to 32 bit with transparencies.. So please you Pro Mattepainters enlighten me!!!
 
Old 12-07-2012, 02:25 PM   #2
CarlEd
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Quote:
Originally Posted by olli20
Hi there!

I got an interesting problem which I assume some of you may have run into. The problem is as follows:
I do my Mattepainting in 16 bit in PS and want to export it to Comp.To make it nice and clean I want to export a layered EXR file from Photoshop. So here comes the hazzle! To be able to export an 16 bit exr from PS I have to switch my Mode to 32 bit. And here it comes, halftransparent pixels become more opaque, which is quite a pain for stuff like fog etc..

So I got a question to you guys! How do you handle multilayered Mattepaintings pipeline wise?
Do you export each layer seperately with a seperate alpha channel as for instance a .tif file? Or is there a special trick when exporting a layered exr from PS? So nobody really seems to know what PS does exactly when converting an image from 16 to 32 bit with transparencies.. So please you Pro Mattepainters enlighten me!!!


Most larger vfx houses have their own in-house pipeline (and software).
Isn't it pretty obvious what happens when you're changing a lower resolution 16bit file into a higher resolution 32bit image? That extra range of color information won't magically appear out of nowhere. Photoshop does what it can to solve the problem, and voila, you'll get a different looking transparency.

First of all, Photoshop can't save layered EXR files without a specific plugin (ProExr).
The whole idea of working within OpenExr is to keep the 32bit workflow trough-out the pipeline making it easier for comp etc.

If you absolutely need to work with 32-bits multilayer files then buy the plugin. It will make it possible for you to set the level of compression as you want it.
If not then I'll recommend you to save each layer separately as a 16bit transparent .tif file.
Nuke can read psd-files but I'm not sure if it can handle more than 8bit images and you might need to add a python script to gain more control.

If you own a copy of nuke then you can easily write out your .tifs as exr saving some working memory on smaller file sizes (high res tif-files tends to become quite large in terms of size).

Cheers
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Last edited by CarlEd : 12-07-2012 at 02:32 PM. Reason: additional info
 
Old 12-07-2012, 03:10 PM   #3
olli20
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Quote:
Originally Posted by CarlEd
Most larger vfx houses have their own in-house pipeline (and software).
Isn't it pretty obvious what happens when you're changing a lower resolution 16bit file into a higher resolution 32bit image? That extra range of color information won't magically appear out of nowhere. Photoshop does what it can to solve the problem, and voila, you'll get a different looking transparency.

First of all, Photoshop can't save layered EXR files without a specific plugin (ProExr).
The whole idea of working within OpenExr is to keep the 32bit workflow trough-out the pipeline making it easier for comp etc.

If you absolutely need to work with 32-bits multilayer files then buy the plugin. It will make it possible for you to set the level of compression as you want it.
If not then I'll recommend you to save each layer separately as a 16bit transparent .tif file.

If you own a copy of nuke then you can easily write out your .tifs as exr saving some working memory on smaller file sizes (high res tif-files tends to become quite large in terms of size).

Cheers



Hey carl, thanks for your quick reply!

first of all yes, we`re using the plugin to export multilayer exr files. But I dont necessary need a 32 bit full floating file for comp. The problem here is the PS workaround in my opinion. When I paint a 16 bit image I need to convert it to 32 bit files to export it as an exr file.
So I tried to export an 16 bit png with transparency and opened it in Nuke. It comes in Unpremultiplied and in srgb Color Space. So the alpha of the Image has an SrgB Lookup applied too. So when Inverting the SrgB Colorspace from the Alphachannel, it comes somewhat close to the original appearence in PS but not exactly. And this is the point. The Gamma in PS seems to work a bit strange, therefore you cant exactly reproduce or Invert the Lookup that PS applies..I hope it becomes clear what I`m after..

So do you at work export each layer as a 16bit .tif files with an integrated alpha or do you export color and alpha seperately?
So this Problem really becomes obvious with transparent pixels. Working with solid pixels is not so much of a problem.

Working with a layered exr is just because I think it`s really clean and not to messy because you just export one file wit all layers inside..and our whole pipeline is based on exr..

So maybe another question: Do you paint in log colorspace with an icc profile applied or is the plate always converted to SrgB which is a little more painless in PS but with the disadvantage of value clipping?

Thanks oli
 
Old 12-07-2012, 04:03 PM   #4
CarlEd
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Quote:
Originally Posted by olli20
Hey carl, thanks for your quick reply!

first of all yes, we`re using the plugin to export multilayer exr files. But I dont necessary need a 32 bit full floating file for comp. The problem here is the PS workaround in my opinion. When I paint a 16 bit image I need to convert it to 32 bit files to export it as an exr file.
So I tried to export an 16 bit png with transparency and opened it in Nuke. It comes in Unpremultiplied and in srgb Color Space. So the alpha of the Image has an SrgB Lookup applied too. So when Inverting the SrgB Colorspace from the Alphachannel, it comes somewhat close to the original appearence in PS but not exactly. And this is the point. The Gamma in PS seems to work a bit strange, therefore you cant exactly reproduce or Invert the Lookup that PS applies..I hope it becomes clear what I`m after..

So do you at work export each layer as a 16bit .tif files with an integrated alpha or do you export color and alpha seperately?
So this Problem really becomes obvious with transparent pixels. Working with solid pixels is not so much of a problem.

Working with a layered exr is just because I think it`s really clean and not to messy because you just export one file wit all layers inside..and our whole pipeline is based on exr..

So maybe another question: Do you paint in log colorspace with an icc profile applied or is the plate always converted to SrgB which is a little more painless in PS but with the disadvantage of value clipping?

Thanks oli

Is see what you're after but it seems like you're creating way to many problems just for the benefit of getting everything exported in one exr-file. I would have kept it simple, just exporting each layer separate as a 16bit transparent tif and then converting it in nuke to exr if you want to save some time and memory. They layer function is far from perfect as far as I know (maybe this will be different in the next version of nuke). Photoshop is known for doing a bad job exporting perfect exr's so I would avoid it.

Usually each layer is exported as a 16bit tif with an integrated alpha.
I always work on scanned log plates that requires a log colorspace and an applied icc profile. Working in sRGB is not an option.
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Last edited by CarlEd : 12-07-2012 at 04:25 PM.
 
Old 12-08-2012, 01:48 PM   #5
olli20
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okay cool thanks for the info, I was just curious about how the workflow is being handled in other MP Departments and maybe if I`m just missing the point somewhere in the exr export process. But it seems to me that adobe has to make some Improvements in terms of colorspace handling... Its so much more uncomplicated in foundry software for example!

cheers oli
 
Old 07-25-2013, 07:53 PM   #6
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32bit float

You are discribing multiple issues there and there are several solutions to each, depending on the pipeline and worklow of each studio. Photoshop's gamma discrepancy comes from it working in sRGB with a gamma of 2.2 and a 16bit depth. Nuke is a float platform and converts everything when you read in a file. The colourspace drop-down menu is actually specifying what to convert the footage/image from; not what to convert it to, as everything is getting linearized, in order to be working in one colour space, as opposed to Shake, where you could switch. This is also the reason why you can't switch the bit depth within Nuke while working, even though you could technically write it out at a lower bit depth. The issue is that you are shifting a range of 0 to 1 into super white beyond 1 and black beneath 0 (uncommon). That way your transparent pixels shift into a different shade of grey. True, Photoshop does a different conversion then Nuke, resulting in a "sadly" worse gamma shift but there are
a) controls for this within Photoshop
b) Plug-ins for exactly this that you can install in Photoshop

Theory aside, you have 2 immediate options:
1. Save out a PSD (not PSB) without layer masks or adjustment layers and bring it into Nuke, using "Breakout Layers". It post-multiplies each layer and writes an alpha into metadata. Works a charm under 6k and unless you start analysing value numbers by the pixel, you won't notice the shift by eye. However, there's still a minor shift that you'll notice when comping smoke or fire. As smoke and fire are usually not part of a DMP, you should be fine. However, for maximum German efficiency and control, use option two.
2. Save each layer out as a post-multiplied RGB TIF file at 16bit without an alpha. Do not embed the alpha. By post multiplied I mean running an action that duplicates your layer about 200times and flattens it back down to get rid of the transparent pixels. Make sure after you save out your alpha of each layer, you convert those RGB TIF files to 8bit, otherwise you'll get the same result as with the PSD.
Then read in the colour layers as Cineon and the alphas as "linear" into Nuke. This is assuming you're working with log film files, not some DSLR footage or something. Shuffle your RGB alpha into the actual alpha, making the file RGBA. Select the alpha node and then shift-select your colour and hit "K" on the keyboard to switchmatte it over.
Premult it and Nuke will not have shifted your transparent pixels.


Hope this helps.
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Last edited by milanschere : 07-25-2013 at 10:49 PM. Reason: More specification.
 
Old 07-25-2013, 07:53 PM   #7
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