This one has been on my mind for some time, and I guess if it keeps gnawing somewhere in my brain I need to figure it out .
Can some of you help me on my way - or help me, period - to figure out what Nik Color Efex ‘Skylight’ filter is doing?
I use if often on series of batch images that have a bit of ‘dirty’ warmth to them. By fixing the yellow cast but then adding this ‘skylight’ filter (which doesn’t just add yellow everywhere the same amount) it seems to clean up the colors a lot while still keeping warm tone.
I thought I was close lately by using a ‘Reflect’ blend-mode with a luma-mask and the color of a warming gel/filter, but it’s not as clean as this filter does .
Of course, there are a lot of people that might not use Nik’s suite or even the Skylight filter in it, and have no interest in it. I thought I add three hald cluts, in not too big a resolution. One with the effect applied for the full 100%, one at 50% and one at the (default usage) 20%. The effect is applied / meant for regular sRGB pictures.
From playing with a color sampler in before/after shots, I don’t see a real pattern yet in RGB / CMYK modes. I also tried in lab, but apart from an increase in the L channel I don’t see much repeatable (sometimes the a channel increases, sometimes it doesn’t, same for b channel, etc…).
The best I can think of is that it’s working in some HSB / HCL / HSV space, it scales/boosts the L a bit, it scales/boosts the saturation a bit, and it seems to push colors ‘toward red’ a bit. Like, the more red in a color, the more it’s pushed towards red, the more ‘blueish’ a color is, the smaller the hue shift. But I’m only guessing here.
Does someone have some tricks, methods or insights in how to figure out what is being done here?