Hi. Brigthtness Curves Make incorrect Color. In my test it must be black if i muve right point to the bottom. Here is screenshot: http://i.imgur.com/USUPUk5.png Here is the file: https://dl.dropboxusercontent.com/u/26887202/Krita/test_curve.psd RGB channels must become 000 values.
Also, it's good to check RGBA Curves filter too. Possibly it's bugged too.
The Krita color curves dialog makes everything black -- though we need an option there to adjust RGB channels in one go, instead of every channel separately. There is no brightness/contrast curves dialog in Photoshop or Gimp, and Gimp's B&C slider dialog gives a different result from Photoshop's B&C slider dialog. Gimp makes everything gray if I move both sliders to the left-most position, Photoshop makes everything black. In Krita we don't do the calculations ourselves: we pass the curve to lcms and lcms does the adjustments. lcms goes through lab to to determine brightness/contrast, and it's likely that there is some rounding involved. I don't know whether we can actually fix this in Krita, or whether we need to refer it to Marti.
Guys. This is color correction. This is basic of this. We really need to fix it. Gimp and PS are ok in this area of curves correction. Here is just the same result from Gimp http://i.imgur.com/F0PlPL4.png Possibly it's time to rewrite RGBA and Brightnes/Contrast curves into one good curves tool? Like PS/Gimp/Natron have.
this was resolved with rgba curve.