Saved images appear faded compared to graphics window, need color profiles

[goddard@…]

The following bug report has been submitted:
Platform:        Darwin-19.3.0-x86_64-i386-64bit
ChimeraX Version: 0.92 (2020-01-29)
Description
Saved image appears faded compared to ChimeraX graphics window appearance when image is shown with Preview on iMac.  The problem is the saved image does not have a color profile.

Log:
UCSF ChimeraX version: 0.92 (2020-01-29)  
© 2016-2020 Regents of the University of California. All rights reserved.  
How to cite UCSF ChimeraX  

> open 1547 fromDatabase emdb

Opened emd_1547.map, grid size 160,160,160, pixel 2.8, shown at level 0.231,
step 1, values float32  

> open 1283 fromDatabase emdb

Opened emd_1283.map, grid size 120,120,120, pixel 2.5, shown at level 0.399,
step 1, values float32  

> select #2

2 models selected  

> ui mousemode rightMode "translate selected models"

> volume #2 color #ff00f2

> volume #2 color #ff1cff

> volume #2 color #ff71f9

> volume #2 color #ff6efa

> volume #1 color #0eba5f

> volume #1 color #53b87e

> volume #1 color #53b87e78

> volume #1 color #5ed29078

> volume #1 color #6cf4a678

> volume #1 color #62db9678

> select clear

> lighting soft

> save /Users/goddard/Desktop/image1.png supersample 3

> save /Users/goddard/Desktop/test2.png supersample 1

> save /Users/goddard/Desktop/test3.png supersample 1




OpenGL version: 4.1 ATI-3.5.5
OpenGL renderer: AMD Radeon Pro 580 OpenGL Engine
OpenGL vendor: ATI Technologies Inc.

[Tom Goddard]

This problem was originally reported by Christophe Leterrier

​http://plato.cgl.ucsf.edu/pipermail/chimerax-users/2020-January/000834.html

[Tom Goddard]

Begin forwarded message:

From: Tom Goddard
Subject: Re: [chimerax-users] Colors from snapshots
Date: January 29, 2020 at 12:19:22 PM PST
To: Christophe Leterrier
Cc: ChimeraX Users Help <chimerax-users@…>

Hi Christophe,

The reason the on-screen ChimeraX image appearance is different from the saved image is because the saved image "color profile". On my iMac (macOS 10.15.3, 27" 5k retina display) if I screen capture (using command-shift-4) a scene similar to yours (same colors and transparency) and also save an image with "save test.png supersample 1" I find just as you do that the test.png image shown by Preview has less saturated colors then the screen capture. In Preview I use menu Tools / Show Inspector and it says my screen capture is using "ColorSync profile: iMac" and shows test.png has "ColorSync profile: -". If I use the macOS ColorSync Utility as described here

​https://support.apple.com/lt-lt/guide/colorsync-utility/csyncad0012c/mac

to assign the iMac ColorSync profile to test.png then my test.png has the same saturated colors as the screen capture.

So I believe the RGB pixel values in the screen capture and the ChimeraX saved image are identical and that they appear different on screen in Preview because of different color profiles. ChimeraX does not specify a color profile in the images it saves. It is using the Python Image Library (actually the Pillow fork). It is possible to set icc_profile for jpeg and png images in pillow, but it is not clear how to get the iMac profile or whatever profile is used on Windows and Linux -- probably need to query the operating system for what color profile is being used for the display.

Using macOS ColorSync Utility I tried sRGB IEC61966-2.1 profile also and it looked identical to the None profile on my iMac. There were a dozen other profile choices in the ColorSync Utility and they give quite different appearance, for example, Display P3 looks the same as the iMac profile while "Generic RGB Profile" looks even more faded than the saved ChimeraX image.

I think ideally ChimeraX would save the color profile being used on your display. But we don't have the resources to delve into how to implement that. I've made a ChimeraX bug report to describe the problem.

​https://plato.cgl.ucsf.edu/trac/ChimeraX/ticket/2787

Tom

[Tom Goddard]

Will leave this as an enhancement request to save color profile with images.