Photoshop: Difference blend mode change from 8 bit to 16 bit

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  • Problem
  • Updated 3 months ago
  • (Edited)
In Photoshop most blend modes act the same whether Opacity is 100% and Fill is 50% as to when Opacity is 50% and Fill is 100%.
Some , such as Linear Dodge, Vivid Light. Hard Mix, Color Burn, Color Dodge act differently when you reverse the Fill and Opacity settings and that is OK.

However there is one Blend Mode - Difference which acts differently when reversing Fill and Opacity in 8 bits/channel but acts the same when reversing those settings in 16 bits/channel.

This has the knock on effect of a considerable change the image blend when going from 16 bits to 8 bits or vice versa (and that includes zooming between 66.7% and 50% where the previews switch from 16 bit to 8 bit blending)

To replicate
Create a document with 16 bits/channel (I used Pro photo but it happens in all spaces)

Fill a layer with 128.128 ,128
Fill a layer above with 161.159,156
Set blending mode of upper layer to difference
Set Opacity of upper Layer to 100% and Fill to 65%
Now zoom between 66.7% and 50% and watch the blend change !

The same happens when converting to 8 bits/16 bits

Dave
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David Richardson

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Posted 6 months ago

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Yves Crausaz

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macOS 10.14.5 / PS 20.0.5 I can not reproduce this problem?


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David Richardson

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Thanks for testing Yves.

I use Windows 10 (v1809) and can reproduce in both 20.0.5 and 19.1.8
Two others also confirmed. It came out of an issue raised by a user on the Photoshop community forum where at first I thought it was just down to the normal differences between 8 and 16 bit blends when zooming but I was then able to track it down to this.

https://forums.adobe.com/thread/2631572

Dave



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Dennis Geller

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I think I have found another manifestation of the same problem.

I have an image with two layers. The top layer is set to Difference blend mode and Fill of 61%. When I save from PS and look at it in LR it looks wrong. I have tried saving as PSD or TIFF or JPG, and all look wrong -- almost as if the FIll was being read as 100, but not quite. Not only do the LR views and the saved JPEGs look wrong, but using Apple's Preview on the TIFF file (which looks correct in PS) also shows the wrong version of the image.

One oddity: at one point I saved the image and imported it into LR (rather than letting the import happen in the background). I saw the correct version of the image on the import screen for a second, and than it was overwritten by the incorrect version. 

I saw a mention of this thread on https://forums.adobe.com/message/11239074#11239074 and so I tried changing my image to 8 bit. Now it looks correct in both LR and in saved JPEGs.



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David Converse

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I reported a bug and sent a sample PSD to Adobe regarding this issue. They are working on a new compositing engine and hopefully stuff like that gets fixed up.
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Dennis Geller

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Thanks.