There's definitely a difference between Tweak(sat=0.5) and reducing the saturation by 127 with Irfanview. I can easily see it when I use the following on your original image.
ConvertToYV12(matrix="rec709")
Tweak(Sat=0.50, coring=false)
I'm wondering if it's somehow gamma related. By reducing the gamma to 90% with Irfanview while reducing the saturation by a little more than 50% I can get it fairly close to what Tweak does, but I still haven't managed to find a combination that produces the same result.
Edit: No, after a bit more playing around I don't think it's gamma. Tweak(sat=0.52) is closer to Irfanview's 50% although reds still aren't the same.
Last edited by hello_hello; 7th December 2017 at 23:22.
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