Display RGB channels shows alpha premultiplied color with 8-bit images #83342

New Issue

Jose Conseco · 2020-12-03T00:44:40+01:00

Jose Conseco commented

2020-12-03 00:44:40 +01:00

System Information
Operating system: Linux-5.8.18-1-MANJARO-x86_64-with-arch-Manjaro-Linux 64 Bits
Graphics card: GeForce GTX 1660 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 440.100

Blender Version
Broken: version: 2.91.0, branch: master, commit date: 2020-11-25 08:34, hash: 0f45cab862
Worked: blender-2.90.1

Short description of error
Display RGB channels shows alpha premultiplied color with 8-bit images. See sampled color in image editor. It should be all white

Sorry for using sequencer to demonstrate this, it was quickest method to render data I need.

Exact steps for others to reproduce the error
#83342.blend

Open file
Render

Sample color in black area in image editor

RGB channels have value of 1, pixels are black however.

**System Information** Operating system: Linux-5.8.18-1-MANJARO-x86_64-with-arch-Manjaro-Linux 64 Bits Graphics card: GeForce GTX 1660 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 440.100 **Blender Version** Broken: version: 2.91.0, branch: master, commit date: 2020-11-25 08:34, hash: `0f45cab862` Worked: blender-2.90.1 **Short description of error** Display RGB channels shows alpha premultiplied color with 8-bit images. See sampled color in image editor. It should be all white ![untitled.png](https://archive.blender.org/developer/F9524611/untitled.png) Sorry for using sequencer to demonstrate this, it was quickest method to render data I need. **Exact steps for others to reproduce the error** [#83342.blend](https://archive.blender.org/developer/F9524630/T83342.blend) - Open file - Render # Sample color in black area in image editor RGB channels have value of 1, pixels are black however.

Jose Conseco commented

2020-12-03 00:44:40 +01:00

Added subscriber: @JoseConseco

Evan Wilson commented

2020-12-04 05:28:21 +01:00

Added subscriber: @EAW

Evan Wilson commented

2020-12-04 05:28:21 +01:00

Changed status from 'Needs Triage' to: 'Needs User Info'

Evan Wilson commented

2020-12-04 05:28:21 +01:00

Code in question for other Triagers:

import numpy as np

if "TestImg.png" not in bpy.data.images.keys():

bpy.data.images.new("TestImg.png", width=128, height=128, alpha=True, float_buffer=False)

outputImg = bpy.data.images["TestImg.png"] 
outputImg.alpha_mode = 'STRAIGHT'
outputImg.file_format = 'TARGA' #does nothing
np_out_img = np.ones((128,128,4), dtype = np.float16)

# disable line below  to see it affects not only A channel. It should not affect RBG channels
np_out_img[:,:30,-1]=0 # set left half  Alpha channel) to black - 
outputImg.pixels = np_out_img.ravel()  #flatten the array to 1 dimension and write it to testImg pixels```

With the caveat that I don't know much about python as other Triagers, the results for me are the same using 2.83.8, 2.90.1, 2.91.0, and 2.92 cc6ec71b1934.

Opening the file, there is an image with RGBA values of (0, 0, 0, 1)
![TestImg_before running.png](https://archive.blender.org/developer/F9475523/TestImg_before_running.png)

Running the script produces an image with RGBA values of (1, 1, 1, 0) in the left 30 pixels of the image, and (1, 1, 1, 1) in the rest.

2.90
![2.90_double_check_TestImg.png](https://archive.blender.org/developer/F9475531/2.90_double_check_TestImg.png)

2.91
![2.91_double_check_TestImg.png](https://archive.blender.org/developer/F9475533/2.91_double_check_TestImg.png)

Checking and seeing that the RGB values are all 1 for the entire image, and only the Alpha has changed.
![Gimp_RGB_are_still_1.0.png](https://archive.blender.org/developer/F9475535/Gimp_RGB_are_still_1.0.png)

Commenting out line 12 produces an image where all values are 1.
![TestImg_line12_commented_outpng.png](https://archive.blender.org/developer/F9475545/TestImg_line12_commented_outpng.png)

What difference do you see on your system?

What version of python and numpy are you running?

Code in question for other Triagers: ```import bpy import numpy as np if "TestImg.png" not in bpy.data.images.keys(): ``` bpy.data.images.new("TestImg.png", width=128, height=128, alpha=True, float_buffer=False) ``` outputImg = bpy.data.images["TestImg.png"] outputImg.alpha_mode = 'STRAIGHT' outputImg.file_format = 'TARGA' #does nothing np_out_img = np.ones((128,128,4), dtype = np.float16) # disable line below to see it affects not only A channel. It should not affect RBG channels np_out_img[:,:30,-1]=0 # set left half Alpha channel) to black - outputImg.pixels = np_out_img.ravel() #flatten the array to 1 dimension and write it to testImg pixels``` With the caveat that I don't know much about python as other Triagers, the results for me are the same using 2.83.8, 2.90.1, 2.91.0, and 2.92 cc6ec71b1934. Opening the file, there is an image with RGBA values of (0, 0, 0, 1) ![TestImg_before running.png](https://archive.blender.org/developer/F9475523/TestImg_before_running.png) Running the script produces an image with RGBA values of (1, 1, 1, 0) in the left 30 pixels of the image, and (1, 1, 1, 1) in the rest. 2.90 ![2.90_double_check_TestImg.png](https://archive.blender.org/developer/F9475531/2.90_double_check_TestImg.png) 2.91 ![2.91_double_check_TestImg.png](https://archive.blender.org/developer/F9475533/2.91_double_check_TestImg.png) Checking and seeing that the RGB values are all 1 for the entire image, and only the Alpha has changed. ![Gimp_RGB_are_still_1.0.png](https://archive.blender.org/developer/F9475535/Gimp_RGB_are_still_1.0.png) Commenting out line 12 produces an image where all values are 1. ![TestImg_line12_commented_outpng.png](https://archive.blender.org/developer/F9475545/TestImg_line12_commented_outpng.png) What difference do you see on your system? What version of python and numpy are you running?

Jose Conseco commented

2020-12-04 13:47:13 +01:00

I just did fresh install of official 2.91, this time on windows 10, with default settings and still RBG is multiplied by A
Python: 3.7.7
Numpy shows version: 1.17.5

Btw you can check RBG channels in the top-right corner of blender image editor.
And it works in blender 2.90 and below versions on both windows and linux . Looks like its not OS related.

I just did fresh install of official 2.91, this time on windows 10, with default settings and still RBG is multiplied by A Python: 3.7.7 Numpy shows version: 1.17.5 ![image.png](https://archive.blender.org/developer/F9476765/image.png) Btw you can check RBG channels in the top-right corner of blender image editor. And it works in blender 2.90 and below versions on both windows and linux . Looks like its not OS related.

Jose Conseco commented

2020-12-15 14:28:24 +01:00

Changed status from 'Needs User Info' to: 'Needs Triage'

Jose Conseco commented

2020-12-15 14:28:24 +01:00

Since I have additional info I change status of report back to Need Triage

Richard Antalik changed title from ~~Alpha channel value affects RGB channels brightness when set form img.pixels~~ to Display RGB channels shows alpha premultiplied color with 8-bit images

2020-12-22 07:07:32 +01:00

Richard Antalik commented

2020-12-22 07:07:32 +01:00

Changed status from 'Needs Triage' to: 'Confirmed'

Evan Wilson commented

2022-06-12 02:33:51 +02:00

It appears I have had a reply saved in Phabricator that I never sent. Sorry about that.

Thank you for clarifying. I now understand and can reproduce the display issue. It appears that Blender is multiplying the alpha and color channels together before displaying them, even when inspecting the color channels alone.

In the following picture, my mouse is in the black part of the image, and the display channels are set to color.

It appears I have had a reply saved in Phabricator that I never sent. Sorry about that. --- Thank you for clarifying. I now understand and can reproduce the display issue. It appears that Blender is multiplying the alpha and color channels together before displaying them, even when inspecting the color channels alone. In the following picture, my mouse is in the `black` part of the image, and the display channels are set to `color`. ![2.92_Image_editor_SS_color_annotated.png](https://archive.blender.org/developer/F9500564/2.92_Image_editor_SS_color_annotated.png)

Philipp Oeser removed the

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Display RGB channels shows alpha premultiplied color with 8-bit images #83342

Sample color in black area in image editor