To make a photo grayscale in Krita, follow the following steps:
1: open the image you want to edit in Krita.
2: add a new filter layer to the the image. The filter we want is the Adjust -> Desaturate filter.
3: the desaturate filter offers multiple desaturation methods to choose from. The meaning of these options are documented in Krita's manual:
Lightness
This will turn colors to gray using the HSL model.Luminosity (ITU-R BT.709)
Will turn the color to gray by using the appropriate amount of weighting per channel according to ITU-R BT.709.Luminosity (ITU-R BT.601)
Will turn the color to gray by using the appropriate amount of weighting per channel according to ITU-R BT.601.Average
Will make an average of all channels.Min
Subtracts all from one another to find the gray value.Max
https://docs.krita.org/en/reference_manual/filters/adjust.html#desaturate (accessed 2024-06-29)
Adds all channels together to get a gray value.
The default setting is "Lightness," which, by my interpretation of the above, converts RGB to HSL, sets the Saturation to 0, and converts it back to RGB. While this may sound like it makes sense, this is actually a terrible idea for us because it will give us a very poor result for photography.
Instead, select "Luminosity," which better matches how light and saturation are perceived by humans. There are two standards, 709 is the modern one, 601 is an older one. Either is better than the default.
After you finished configured the filter, click OK to apply it. Having done it, the image will be in grayscale.
4: optional: select the "desaturate" filter-layer you created and add a filter-mask to it (either "levels" or "color adjustment curves") to change the brightness and contrast of the image.
5: save the image.
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