Luminous Landscape Forum

Raw & Post Processing, Printing => Digital Image Processing => Topic started by: Doug Gray on January 16, 2019, 07:52:04 pm

Title: Photoshop 2018 CC Bug - Wrong RGB pixel readings
Post by: Doug Gray on January 16, 2019, 07:52:04 pm
Load the attached 8 bit file in Adobe RGB. It is 16x16 and has all 256 neutral colors, Top to bottom, left to right.

Zoom to 3200% to make it easy to read each pixel. Make sure the picker is in single pixel mode. The 7th and 8th rows read as duplicates of each other.

But they are not as confirmed on multiple, other programs.

This effect occurs on both my main system with V 20.0.1  and a laptop with V 20.0.2. Both are Win 10 x64.

It's the Info panel that's wrong. If you actually use the color picker to pick a color it picks correctly.
Title: Re: Photoshop 2018 CC Bug - Wrong RGB pixel readings
Post by: FranciscoDisilvestro on January 16, 2019, 08:07:55 pm
It works fine on mine, Photoshop 20.0.2, Windows 10 64 bit
Title: Re: Photoshop 2018 CC Bug - Wrong RGB pixel readings
Post by: digitaldog on January 16, 2019, 08:48:36 pm
It works fine on mine, Photoshop 20.0.2, Windows 10 64 bit
Ditto on Mac, latest version; all unique values.
Title: Re: Photoshop 2018 CC Bug - Wrong RGB pixel readings
Post by: Doug Gray on January 16, 2019, 09:27:23 pm
Interesting. My two systems:

Microsoft Surface Book, 16G ram Win 10 x64 with the Dec. features update, PS 20.0.2
DIY system, about 8 years old 980X with 24K ram, Nvidia quadro K2000D, w/o the Dec. Win 10 update,  PS 20.0.1

Both show the same duplicate of rows 7 and 8 (row 8 shows the same values as row 7) in the Info panel but the color picker sees (when clicked) the correct values.
Title: Re: Photoshop 2018 CC Bug - Wrong RGB pixel readings
Post by: FranciscoDisilvestro on January 16, 2019, 09:35:35 pm
Have you tried to display the info in 16 bits to see if there is any change? Also, try turning on/off GPU

My System: HP Zbook G4 mobile workstation, 32 GB RAM, Nvidia Quadro M1200 Windows 10, version 1803
Title: Re: Photoshop 2018 CC Bug - Wrong RGB pixel readings
Post by: Doug Gray on January 16, 2019, 10:44:42 pm
More info, really weird info.

All info 8/16/32 bit settings exhibit the same stuck row values.

No difference with any of the color settings or acceleration. 10 bits/ 8 bits same duplication. Fails.

Tried it on a friend's desktop system, Also current 64x Win 10. Works!

Then I tried dragging the Photoshop App window to my second monitor which is 8 bit cheapo. Works!
Dragged it back to the primary. Fails.

So, thinking what could be the same between the setups that failed? Well, they are all using high DPI displays, except the second display on my system (the one that works) isn't high DPI.

So then I looked at the Windows display magnification settings. My main system was set at 150% while the secondary display was at 100%, these were the default recommended setting. I changed the main to 100%. It now works. Changed it to 200%. Works. But 150% Fails and that's both the default for the 4K monitor and my preferred setting.

So then I changed the Surface Book which was at 225% where it fails to 200%. Works.  Changed to 100% (tiny stuff). Works.

Conclusion: Most likely a Microsoft bug but given the whole row is effected and it makes 2 duplicates, to me it has a memory race condition smell.

I might try disabling all but one of the CPU cores and see if that also fixes it.
Title: Re: Photoshop 2018 CC Bug - Wrong RGB pixel readings
Post by: Doug Gray on January 16, 2019, 11:18:15 pm
Setup it up to use only one cpu core. Slower than molasses but fails the same way.

As an aside, I made a 16x16 image with alternating white/black rows. Same problem. It's kind of disconcerting to see a totally white pixel that shows RGB(0,0,0) on the info panel. So the pixel colors display properly but the info panel shows the prior row's values.

Since the problem stays, even with one core operating, it's not a memory race condition between threads. Just some old fashioned bug somehow related to the display magnification setting in Windows.

Some good news. Even though the info panel shows the wrong values (row 8 duplicated from row 7), making a layer copy works correctly. So whatever is feeding the info panel data isn't replicated doing real work. So the bug doesn't seem to be messing anything up other than the info panel data. And only with high DPI magnification settings in Windows that are not multiples of 100%. And maybe only on some systems at that.
Title: Re: Photoshop 2018 CC Bug - Wrong RGB pixel readings
Post by: 32BT on January 17, 2019, 03:11:30 am
Smells like a rounding error from the system reporting the cursor location. The vertical location might need to be flipped somewhere. Rounding before or after this flip may yield different results.

Does it also happen in the horizontal direction? 

ps. Doesn't 150% viewing make it harder to judge sharpning settings e.a.?
Title: Re: Photoshop 2018 CC Bug - Wrong RGB pixel readings
Post by: kers on January 17, 2019, 06:08:36 am
photoshop 19.1.7 on a mac-   no problem
Title: Re: Photoshop 2018 CC Bug - Wrong RGB pixel readings
Post by: Aram Hăvărneanu on January 17, 2019, 06:29:01 am
Excellent debugging Doug.

Even years after Microsoft started implementing HiDPI support, it's still not working properly and not supported by a huge array of applications. Unbelievable.
Title: Re: Photoshop 2018 CC Bug - Wrong RGB pixel readings
Post by: TonyW on January 17, 2019, 10:58:09 am
FWIW all unique RGB numbers without repeat (Info Panel and Colour Picker) on my Windows 10 64 bit OS, 16GB RAM GTX960 graphics (8 bit rendering).  Still on PS 19.1.7. 

So it does not seem clear to me and no evidence to support that it is a Windows issue.  Could it be a PS 20.*.* issue under certain conditions i.e. Windows 10 ?
Title: Re: Photoshop 2018 CC Bug - Wrong RGB pixel readings
Post by: Doug Gray on January 17, 2019, 02:09:09 pm
A few additional notes:

I installed CS6 to test ACE per a discussion in the Color Management forum. The Info panel works correctly. OTOH, since Photoshop CS6 doesn't adjust for screen DPI, the menu/dialog fonts are so tiny on my Eizo 4K that Photoshop is close to unusable.