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Bomatick

Colour Change // 32-bit to 16-bit

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Hi folks,

anyone noticed the colour change when converting down from 32-bit to 16-bit?
Searched the forum for a while and it doesn't come up.

I'm working with 32-bit EXR render and at some point you need to convert down to a lower bit depth and when you do any editing on the scene, it changes the colour.
Do the same in Photoshop and it stays correct.

You can try it with anything: Exposure or Curve to make it visible.
Set up the exact same settings in both AP and PS and convert down to 16 bit and then compare both images.
Or even just do it in AP. Have your layer stack in full 32 and change the format down to 16 and then switch back and forth to see the difference.

I think this is a huge drawback. Whatever is handling the conversion in the background, somethings off.


Cheers,
Bo

Edited by Bomatick
spell check :)

// sort of freelancer // professionally designing things digital and IRL // products - gfx - light - UI & UX //

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28 minutes ago, Bomatick said:

Do the same in Photoshop and it stays correct.

At a lower bit depth there are fewer distinct colours to choose from, so the only way to maintain (the appearance of) correct colours in all cases would be to introduce dithering.


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Of course there are fewer colours to choose from, it’s a lower bit depth. :)

 

But why can photoshop manage to do that and AP can’t?

Even when there’s no OCIO involved. Just plain tone mapping through layer stacks. In some way AP is managing/processing colours differently and there shouldn’t be a colour change when reducing the bit depth.

Both programs are set up the same way: same colour workspaces etc. etc.

 

Edit: the change only comes apparent when on top of your tone mapping, you’ll also introduce a curve or exposure, to alter the image. Interestingly, when just converting from higher to lower – without any adjustments –, the image stays unaltered.

Haven’t tested it with anything other than that, but it’s a simple change reproducible all the time and through a couple of EXRs.

 

Edit #2: the bug shouldn’t be system related, since I can reproduce it on other Mac’s as well.

But for scientific reasons: it happened first on the latest Mac OS Sierra with AP also updated to the latest. The iMac in question is a 5K (2015) / AMD M395X 4GB / 32GB RAM

Edited by Bomatick
More info! :)

// sort of freelancer // professionally designing things digital and IRL // products - gfx - light - UI & UX //

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The thing that makes working in this way not ideal is the colour change. Why this happens is the question and how to solve it. :)

Since now I need to stick with Photoshop and pay the Adobe tax, to maintain the workflow.

 

And yes, I need to work with 32-bit renders, right now since these are the renders I made (and re-rendering is too costly) and sometimes, because colleagues & customers ship me 32-stuff.

Further down the line there’s always 16/8 bit stuff, but when you handle HDR stuff (whether it’s HDR from a camera or CGI) at some point you’ll stumble upon this. And a colour change isn’t ideal to work around.

 

So there’s something underneath the hood that AP handles fundamentally different than PS. As I said: both workspaces are setup identical, both work with the same material and the same original ECI profiles, as well as OCIO (Nuke’s default at the moment).

 

All I need is a way this colour change does not happen – next to plain tonemapping and work from there. I double checked the colour profile settings, but unless there’s a hidden mechanic working behind the curtain which I can’t control, everything is set up the right way.

 

Cheers :)


// sort of freelancer // professionally designing things digital and IRL // products - gfx - light - UI & UX //

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3 hours ago, >|< said:

There is no colour change when doing what I suggested. Maybe you misunderstood my message.

Work in Affinity's 32 bpc mode to layer and adjust your HDR renders. When you need a 16 bpc output, do not convert the layered Affinity document to 16 bpc. Instead, export to a 16 bpc file such as a PNG containing just a composite image.

  

Thanks for the suggest.

This could be a workaround.
But it immediately raises the question if this would also alter the image. Of course it will, that's the nature if you stay linear all the way through, then you'll need to compromise in the end when exporting to a format of lesser quality and/or one that doesn't support your colour space (or simply you need the old SRGB for whatever-web-stuff) etc.

I have to admit, that I don't have that much experience in AP as in PS – so I know there's the 'Export' and 'Export Persona' – but when it comes to downsampling I'd like to convert directly inside my file and save it out as a lower bit depth and from there I'd work my way through all the exporting and so on. So I'd like full control over the sampling process (bit & colour-space wise). Also working in 16bit keeps the file size down as well.

Edited by Bomatick
typo

// sort of freelancer // professionally designing things digital and IRL // products - gfx - light - UI & UX //

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