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Inconsistent rendering of the lightness of transparent pixels.

Explorer ,
Sep 23, 2024 Sep 23, 2024

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ISSUE:


Inconsistent rendering of the lightness of transparent pixels.
 
The Context


the lightness of transparent pixels on a photoshop document is normally calculated using the gamma the document. In the case of AdobeRGB (1998) the document gamma is 2.2.


Alternatively the user can select a different gamma using “Blend RGB Colours Using Gamma”. Such as 1.00 for colorimetric accuracy.
 
The inconsistency


However, with both “Blend RGB Colours Using Gamma” and the document both set to gamma 2.2,  (e.g by using an AdobeRGB (1998) canvas), It should make no difference to the rendering of transparent pixels if  “Blend RGB Colours Using Gamma” is on or off. Because both the document and the “Blend RGB Colours Using Gamma” are using the same gamma (2.2).
 
However, there is a difference between them, in how they render the lightness of transparent pixels .
This suggests that the math being used for “Blend RGB Colours Using Gamma” is not consistent  with the math used when the pixel lightness is calculated when using the document gamma.
 
Mac OS 14.6

Photoshop: 25.12
 
Steps to reproduce:


1: Make an AdobeRGB (1998) black canvas.


2: On a transparent layer above this canvas make a selection and fill that selection with white pixels. And set this layer opacity to 5%


3: Drop a color sampler over the semi-transparent white area. Set the sampler to show RGB numbers.


4: Set “Blend RGB Colours Using Gamma” = 2.2


5: Toggle “Blend RGB Colours Using Gamma” = 2.2 ON/OFF

Expected Result.


There will be no difference to the rendering of lightness of the transparent white pixels when “Blend RGB Colours Using Gamma” is either ON or OFF. Because the gamma of the document and the gamma of “Blend RGB Colours Using Gamma” are the same (2.2).


Actual behaviour
.

There is a change in the brightness of the 5% white pixel when “Blend RGB Colours Using Gamma” is either ON or OFF, 
ON 26, 26, 26 (RGB)
OFF 13, 13 ,13 (RGB)

 

Blend RGB using gamma - screenshot.jpg

Bug Unresolved
TOPICS
macOS

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4 Comments
Community Expert ,
Oct 07, 2024 Oct 07, 2024

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Curiously it seems the same does not apply when using a black Layer at 5% Fill on a white background. 

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Community Expert ,
Oct 07, 2024 Oct 07, 2024

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@jorisv58887051 , I have refrained from reporting your insolent post, but I recommend you mind your manners in the future. 

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New Here ,
Oct 07, 2024 Oct 07, 2024

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rip lmao, mad ?

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Community Expert ,
Oct 07, 2024 Oct 07, 2024

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Wan’s justament unverstaendlich posten, isch schwea, Sie eanst zu nemma. 

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