I am using Inkscape for vector and Gimp for raster graphics. They are quite powerful though open-source.
Can somebody recommend me if there is open-source software like Inkscape or Gimp or maybe a tool inside mentioned ones that can calculate 75% darker color of a given color?
Well 75% is not a requirement, it can be for example 50% or 42%, whatever. Also could I do the same thing for 75% lighter color or 64% lighter color.
I am building a software and so far I relied on my coded function to calculate given value. But I need to test this function. I need a proof from outside world that this function is calculating the correct value.