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shojtsy

[AP 1.6] Apply Image equations broken in LAB space

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When using Apply Image equations, I am expecting to see a completely greyscale image when Da and Db are set to constant 0 in LAB space, however I see a heavy blue tint. See attached screenshot, left side should be greyscale instead.

 

Apply_image_LAB_space_not_gray.jpg

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Hi shojtsy

 

I'm not too hot on equations, but if you use 1 or -1 instead  of 0 you get a greyscale image. I'll have to look into whether this is correct or not but it should allow you to continue

 

cheers


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Thanks.

However I am afraid that Da=1 and Db=1 is only almost greyscale with a slight blue tint. Note the RGB values in the Info panel below, not showing the same R, G, B values. By the way, the bug is not limited to the value 0, if I set -30 to both Da and Db, then use the Info panel to look at the LAB values in pixels of the resulting image, they vary wildly, and are never -30, -30.

Apply_image_LAB_space_not_gray2.jpg

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After long experimentation I think that LAB channels equations understand DL channel as floating numbers between 0 to 1, but Da and Db channels are floating numbers between 0 and 1.99 with 1 being approximately the neutral color. This is not intuitive and contradicts the scales of the LAB channel values shown in Info panel for pixels in the image.

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