On Tue, 25 Mar 2025, Andrea paz via Cin wrote:
Gimp
E = 1/255*(D*S)
Instead, CinGG's formula is:
[(Sa+Da-Sa*Da), Sc*(1-Da)+Dc*(1-Sa)+Sc*Dc]
I cannot compare the two formulas, there is one too many Sc*(1-Da) and one too many Dc*(1-Sa), and a 1/255 is missing.
Andrea, 1/255 is just the normalization coefficient to bring the unsigned byte range [0-255] to the normalized range [0.0-1.0]. This coefficient is correct for (and only for) the color model RGB 8-bit. For CinGG the things are more variative. For example, if we have RGB-10bit, RGB-12bit, etc. than the 1/255 coefficient is not valid any more. In addition, CinGG has color model RGB-float whose range is [0.0-1.0] already and requires no normalization coefficient at all. To make it easier and more consistent, Blend Algebra transforms the actual color model to float and brings it in the range [0.0-1.0] before executing user's function. Thus, the 1/255, or whatever normalization coefficient in Blend Algebra is taken into account intrinsically.
There are three types of blends whose formulas differ (and which I wanted to implement via Blend Algebra): (Normal); Addition; Subtract and Divide.
Andrea, you can just try your own Blend Algebra functions according to formula of Gimp, modify them and test the resulting look. In Blend Algebra you do not need 1/255, nor any other normalization, it is intrinsic there. Also pay attention, what are source and destination, and the track order in the dialog, sometimes it can be counterintuitive:(
PS: I tried to look for the formulas used by CinCV but I don't know where to find them; do they exist anywhere?
Don't search the working formula in Cinelerra's (any branch) source code, they are horrible. _______________________________________________________________________________ Georgy Salnikov NMR Group Novosibirsk Institute of Organic Chemistry Lavrentjeva, 9, 630090 Novosibirsk, Russia Phone +7-383-3307864 Email [email protected] _______________________________________________________________________________