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Eighteen Shades of Greyscale
Eighteen different formulas for greyscale.
 Set a colour using the sliders, this is then converted to greyscale using eighteen formulas, and you can see each colour’s brightness (i.e. greyscale) value from the chart. Scroll down for an explanation of all the different results. 255 255 255 Base Colour There is another view of greyscale charts at Web Hex:
Greyscales
 calculation type bright 1–4 dark 1–4 like-Photoshop gamma(native) rough-n-ready squared linear Rough-n-Ready gamma rough-n-ready(native) squared linear CIE XYZ gamma rough-n-ready squared linear(native) CCIR601 YIQ gamma rough-n-ready squared linear(native) Lightness linear Average linear
There are different ways to calculate greyscale from a colour. They all work well for different jobs, horses for courses, and very badly for other jobs. Generally, looking at a photo converted to greyscale, it’s nigh-on impossible for the eye to tell the difference, but significant when defining text and manipulating photos.
Key:
 like-Photoshop red_factor 0.2235, green_factor 0.7154, blue_factor 0.0611, exponent 2.4. See Readable Text in Colour – STW*. Note this will set a value that is abolutely like Photoshop only when the calculation type is Gamma (i.e. the native calculation type). Rough-n-Ready red_factor 0.22475, green_factor 0.7154, blue_factor 0.5575, exponent 2.234. This is my simplified approximation to the value achieved with like-Photoshop gamma. See Readable Text in Colour – STW*. The similarity will only pertain when the calculation type is ‘rough-n-ready(native)’. CIE XYZ CIE XYZ coefficients of red_factor 0.2125, green_factor 0.7154, blue_factor 0.0721. The native format is given as linear because that is what many guidelines suggest, though used with a gamma calculation these factors are not far off what you get with Photoshop. CCIR601 YIQ YIQ coefficients also known as Digital CCIR601 and suggested in the Web Accessibility Guidelines from the W3C and challenged by me (see Holes in the W3C Colour Readability Guidelines). Coefficients of red_factor 0.299, green_factor 0.5870, blue_factor 0.114. These factors give quite different results from the like-Photoshop and CIE XYZ factors, and quite why the W3C guideline-devisers suggested these, as of all the options they seem the furthest out in terms of practical use, is one of life’s mysteries still to be explained. Lightness Lightness: ½ × (max(R,G,B) + min(R,G,B)), see Puzzling Greys. Average Average:(R + G + B) ÷ 3, see Puzzling Greys.

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