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Author Topic: Linear spaces look wrong in Photoshop  (Read 13903 times)

markanini

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Re: Linear spaces look wrong in Photoshop
« Reply #20 on: December 24, 2015, 10:35:24 pm »

Well yes, I see a slight difference under 67% but that's a bad idea for all kinds of viewing of image data in Photoshop! And other app's too. You should always be viewing at 100% for an accurate preview. And to answer your other question, I'm using an NEC SpectraView PA272. But if after all this, you're reporting an 'issue' with previews, linear data or not, below 100%, that's not something anyone should be doing. And guess what? IF I convert from Adobe RGB (1998) to sRGB and toggle the two using a view below 67%, there's a difference. So this is kind of a rabbit hole that never needed to be dug into. ;D

Even 4k monitors arent able to view 51mp images above 67% magnification https://en.wikipedia.org/wiki/Canon_EOS_5DS
Also, did you ever try black level adjustments in a linear working space? The adjustment range is very coarse.
« Last Edit: December 24, 2015, 10:44:02 pm by markanini »
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digitaldog

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Re: Linear spaces look wrong in Photoshop
« Reply #21 on: December 24, 2015, 11:06:44 pm »

Even 4k monitors arent able to view 51mp images above 67% magnification https://en.wikipedia.org/wiki/Canon_EOS_5DS
Also, did you ever try black level adjustments in a linear working space? The adjustment range is very coarse.
You're missing the point. The previews below a fixed level are not and have never been accurate in Photoshop. Been that way forever. There's sub-sampling going on and hence, the previews are not accurate. This has nothing to do with the gamma encoding of the data. 100% shows actual pixels!
« Last Edit: December 24, 2015, 11:16:52 pm by digitaldog »
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markanini

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Re: Linear spaces look wrong in Photoshop
« Reply #22 on: December 25, 2015, 08:59:36 am »

You made a point of working on images at 100% which is impractical. I don't agree that all inaccuracies are equal or that one shouldn't expect any accuracy at all for non 1:1 magnification.
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digitaldog

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Re: Linear spaces look wrong in Photoshop
« Reply #23 on: December 25, 2015, 09:19:56 am »

You made a point of working on images at 100% which is impractical. I don't agree that all inaccuracies are equal or that one shouldn't expect any accuracy at all for non 1:1 magnification.
What you reported has absolutely nothing to do with the gamma encoding of the data and has been the expected behavior in PS since 1990!
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markanini

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Re: Linear spaces look wrong in Photoshop
« Reply #24 on: December 25, 2015, 09:23:58 am »

What you reported has absolutely nothing to do with the gamma encoding of the data and has been the expected behavior in PS since 1990!
I don't try to diagnose the problem in the first place, that's why I created a thread to hear what the community had to say.
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digitaldog

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Re: Linear spaces look wrong in Photoshop
« Reply #25 on: December 25, 2015, 09:34:17 am »

I don't try to diagnose the problem in the first place, that's why I created a thread to hear what the community had to say.
You asked in your first post: What's going on? Now you know. This is expected behavior for previewing data in PS and many other app's.
Had you outlined your steps thoroughly by explaining you only see this below a 67% view, you would have received the answer in post #2. This is to be expected and has nothing to do with the gamma encoding. Do you see a change at 100% when you toggle linear or non linear conversions?
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markanini

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Re: Linear spaces look wrong in Photoshop
« Reply #26 on: December 25, 2015, 09:49:04 am »

You asked in your first post: What's going on? Now you know. This is expected behavior for previewing data in PS and many other app's.
Had you outlined your steps thoroughly by explaining you only see this below a 67% view, you would have received the answer in post #2. This is to be expected and has nothing to do with the gamma encoding. Do you see a change at 100% when you toggle linear or non linear conversions?
I wasn't yet aware of the roll magnification played in PS in OP. I also mentioned a another piece of software, GIMP. It still true that it gives the user the convenience of non-posterized display for linear working spaces at all magnifications. So the question still remains as to why PS does not provide the same convenience.
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digitaldog

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Re: Linear spaces look wrong in Photoshop
« Reply #27 on: December 25, 2015, 10:54:40 am »

So the question still remains as to why PS does not provide the same convenience.
The question was answered.
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markanini

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Re: Linear spaces look wrong in Photoshop
« Reply #28 on: December 25, 2015, 12:33:02 pm »

I have updated the OP.
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Doug Gray

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Re: Linear spaces look wrong in Photoshop
« Reply #29 on: December 25, 2015, 05:01:50 pm »

Here are my exact steps:
  • Open an sRGB or AdobeRGB image in Photoshop
  • Convert to a linear(gamma 1.0) RGB color space
  • Convert back to sRGB or AdobeRGB
At this point the image looks the same as from the start as expected. At step 2 however shadows look significantly darker. It's not possible use level adjustments with confience as the image with look different by step 3. I repeat the same steps in this GIMP build http://www.partha.com/downloads/Gimp-2.9.3-color-patched-64bit-portable.exe and unlike in Photoshop I have tonal consistency in step 2. What's going on here?

EDIT: The issue is only visible for magnification factors below 67%. To rule out GPU acceleration bugs you should set Preferences>Performance>Graphics Processor Settings>Advanced Settings...>Drawing Mode:Basic

Another issue with a linear gamma working space in PS is setting black levels. The adjustment range is very coarse.

Does anyone in the community use PS and linear working spaces or do you prefer to use other software? Or do stick to gamma encoded working spaces in PS?
Andrew pointed shadow treatment is a long standing problem with Photoshop showing up in various ways.

I only use gamma=1 for measuring absolute light levels. As Andrew pointed out, banding is there for other gammas too but is more noticeable for gamma=1 in dark shadows because vision is more sensitive to fixed light level changes at low luminance than at high. It appears when displaying images the interpolation process runs in 8 bit mode for display purposes. When looking at values in 16(15 actually) bit RGB mode they are sometimes shown as 15 bit values but rounded to 8 bits.  At other times they are correctly displayed. At least for me. Isn't clear when they are shown incorrectly but I wouldn't trust any eyedropper readings below 100%. GPU and 30bit color makes no difference in my system. Current Photoshop CC, x64 Win10, CG318.

I found this process shows the effect quite strongly.

1. Create a 2000x1500 rectangle in Adobe RGB space, 16 bit.
2. Use a gradient fill going from 0 to 255
3. Convert to gamma=1 RGB.

At 100% the gradient is quite smooth.
At 50% the gradient shows strong shadow banding.

My system switches out of banding when going from 63% to 64%. This appears slightly different from what others see.
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digitaldog

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Re: Linear spaces look wrong in Photoshop
« Reply #30 on: December 25, 2015, 05:25:28 pm »

Andrew pointed shadow treatment is a long standing problem with Photoshop showing up in various ways.
I don't know I'd say it's a long standing problem with Photoshop, lots of other app's behave this way in sub-sampling pixel data when zoomed out. At 100%, we're seeing one image pixel for screen pixel. We see the same preview issues producing moiré patterns too so again, this has absolutely nothing to do with gamma encoding per se, it's just how we have to deal with high rez files subsampled to the screen.
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Doug Gray

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Re: Linear spaces look wrong in Photoshop
« Reply #31 on: December 25, 2015, 05:47:34 pm »

I don't know I'd say it's a long standing problem with Photoshop, lots of other app's behave this way in sub-sampling pixel data when zoomed out. At 100%, we're seeing one image pixel for screen pixel. We see the same preview issues producing moiré patterns too so again, this has absolutely nothing to do with gamma encoding per se, it's just how we have to deal with high rez files subsampled to the screen.

Moire, sure, but subsampling constant 16 bit pixels values is just a bug if they are displayed as if rounding them to 8 bits.  If a group of 16 bit pixels have a values of (60,60,60) , they should be unchanged by subsampling. Adobe Photoshop displays them incorrectly. While the bug shows up when subsampling it is not intrinsic to subsampling. Even the simplest algorithm should leave the values unchanged if their neighbors are the same.
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digitaldog

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Re: Linear spaces look wrong in Photoshop
« Reply #32 on: December 25, 2015, 06:32:01 pm »

Moire, sure, but subsampling constant 16 bit pixels values is just a bug if they are displayed as if rounding them to 8 bits. 
You can call it a bug if you wish. This behavior has been around for 25 years in all kinds of app's that handle pixels.
IF you have an identical grid of pixels, it shouldn’t make any difference if they are 8-bits per color or a higher value. They are the same values. The bottom line is, if accuracy of previews is critical, view at 100% or as it's really occurring and specified in Lightroom, 1:1 (1 image pixel per screen 'dot').


https://helpx.adobe.com/photoshop/using/viewing-images.html#display_images_at_100
Display images at 100%
A zoom setting of 100% provides the most accurate view, because each image pixel is displayed by one monitor pixel. (At other zoom settings, image pixels are interpolated to a different amount of monitor pixels.)
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markanini

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Re: Linear spaces look wrong in Photoshop
« Reply #33 on: December 25, 2015, 09:55:26 pm »

Picasa, Windows Photo Viewer and Irfanview display linear gamma images without posterization. So there's no better reason for PS not to be able to do that other than "it's always done that"?.
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digitaldog

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Re: Linear spaces look wrong in Photoshop
« Reply #34 on: December 25, 2015, 10:27:48 pm »

Picasa, Windows Photo Viewer and Irfanview display linear gamma images without posterization. So there's no better reason for PS not to be able to do that other than "it's always done that"?.
This has nothing to do with linearization or posterization. But whatever. Meanwhile, I'll ask again before moving on: Do you see a change at 100% when you toggle linear or non linear conversions?
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markanini

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Re: Linear spaces look wrong in Photoshop
« Reply #35 on: December 26, 2015, 10:44:21 am »

This has nothing to do with linearization or posterization. But whatever. Meanwhile, I'll ask again before moving on: Do you see a change at 100% when you toggle linear or non linear conversions?
No discernable difference. Can't wait to see what you have in store for me.
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digitaldog

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Re: Linear spaces look wrong in Photoshop
« Reply #36 on: December 26, 2015, 10:58:55 am »

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markanini

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Re: Linear spaces look wrong in Photoshop
« Reply #37 on: December 26, 2015, 11:14:18 am »

Exactly!
Impressive contribution! In what context will you'll find an opportunity to restate the same point for the n-th time next?
« Last Edit: December 26, 2015, 11:43:24 am by markanini »
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