Re: [Gimp-developer] Some blend modes break in unbounded mode sRGB

On 04/09/2014 06:36 PM, Elle Stone wrote:
For Lighten only, Darken only, Multiply, Divide, and some of the other
blend modes, results are *highly dependent* on the color space in which
the blending is done. Removing clipping code doesn't fix the problem.

Here's another blend mode example, this time for the Divide blend mode:


The Divide blend mode assumes the image RGB values are in fact bounded by 0.0 and 1.0, which means technical uses of Divide fail completely after converting a saturated image from its original wider gamut color space to unbounded mode sRGB.

For example, dividing an image by the reddest possible red should send the green and blue channels of all the pixels to 1.0, leaving behind only varying shades of cyan. So after converting a saturated image from its original camera-sized RGB color space to the unbounded mode sRGB color space, dividing by 100% saturated red ("camera red" or sRGB red) failed.

Artistic use of Divide blend mode produces different colors after converting an image to unbounded mode sRGB. In a line drawing produced in the ProPhotoRGB color space, the space between the lines was almost white. In the unbounded mode sRGB color space, the same procedure produced a line drawing with a yellow color cast over much of the image.


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