Hue, Saturation etc. blending modes in Photoshop

[Turgay]

I'm looking for the exact formulation of the hue blending mode in Photoshop.

Ok, I know that hue is coming from the active layer and saturation and luminance are from the base layer.

Hue is hue and luminance is 0,30*R+0,59*G+0,11*B.

But, I could not find which saturation information Photoshop is using for this blending mode. It is not coming from HSB or HSL. Do you know how to calculate saturation for these blending modes?

Thanks.

[herbert]

Hi Turgay,

I would guess it is a straight RGB to HSV/HSL conversion. It then uses the appropriate value for saturation. Note that HSB = HSV. Here is how saturation is calculated for the two colour spaces:

http://en.wikipedia.org/wiki/HSL_and_HSV#Saturation

To test it you would need an appropriate patch colour image of known values. Generate a second one by rotating/inverting the first. You can then cover one with another and see how the blending modes affect the final output pixel values.

If these formulas do not provide the answer then you'll have to do a bit of reverse engineering on Adobe's colour conversions.

Alex

[Turgay]

Thanks Alex, I already looked at the HSB and HSL, but the saturation value is not coming from them, if my calculations are correct. I even tried some chroma formulas, but I couldn't find.

These blending modes, unlike others, uses various color models. Hue is coming from HSB or from HSL (it is same in both of them), luminosity is from YUV. Because, they use different color models, reverse engineering is a little bit difficult in this case, I think.