#Darktable enhance saturation one color software#

SATURATION : colourfulness of an area judged in proportion to its brightness. Saturation is a word that has been abused by decades of bad computer graphics, mixing its scientific meaning with its common usage. It is useful here to reboot the CIE definitions :ĬHROMA : colourfulness of an area judged as a proportion of the brightness of a similarly illuminated area that appears grey, white or highly transmitting. It is therefore a kind of Yuv space, while CIE Lab, JzAzBz, IPT and Oklab are perceptually-uniform (non-radiometrically-scaled) spaces. It is worth noting that Kirk Yrg 2019 is a scene-linear (radiometrically-scaled) space designed for color-grading. The Ych/Yrg rewriting is meant to have an uniform hue repartition around the white point, but has been designed for the sole purpose of having well-scaled GUI controls directly translatable into RGB parameters for algorithms running in scene-referred RGB. It uses the CIE 2006 definition of Y, such that $Y_$. Also, the green range spans too wide on the gradient, compared to other hues, while yellow only has a thin line, and cyan is also compressed. The perceptual hue gradients display no yellow, because yellow is only found at higher luminances and should not appear here. HSL/HSV should display olive-green and light brown in place of yellow, that is, “dark yellow”. It is immediately noticeable that HSL and HSV do not degrade at constant lightness, nor provide constant chroma or “saturation”. For the HSL/HSV models, since luminance and chroma are not defined, S and L/V have been roughly adjusted visually to match the perceptual gradients.

The “saturation” as defined by the HSL space has been proven times and times again to hold no perceptual meaning and finds its origin into the first GUI of limited computers doing integer arithmetic. We can show here another illustration as to why HSL/HSV are meaningless to computer graphics. The following gradients where generated at constant CIE 1931 luminance $Y = 0.4075$ and at constant chroma. For each color model, the chroma has been empirically adjusted to the maximum value that produces a gradient fully contained within sRGB gamut (without clipping).

#Darktable enhance saturation one color software#

The saturation control of pretty much all image processing software is an unfortunate misnomer, to say the least. It actually controls either the chroma in Ych-like spaces (computed from CIE Yxy 1931, Yuv or YCbCr spaces), or some remote idea of saturation as used by HSL spaces, which are essentially a polar rewriting of RGB coordinates (usually expressed in sRGB space). Flatening the model and planning for gamut mapping.Synthetic sweeps at improved hue constancy.Expressing synthetic colours from perceptual hue and chroma.Manipulating real colours at constant hue and chroma.Building a new perceptual color space for color correction.Rewriting Oklab as Brightness-Saturation system.