how to convert CIE color in the following format x = 0.615, y = 0.346, 5.6 cd/m2; to HEX or RGB

Question

Iv'e found converters from xyz, and posts that talk about that posts . but couldnt find a good reference for the 'cd/m2' component of the color

Answer 1

The coordinates you are giving in the question are CIE xyY (small x, small y, BIG Y), they are not CIE XYZ Tristimulus Values (BIG X, BIG Y, BIG Z). The commonality between the two is the Luminance Y. CIE xyY is a perspective projection from CIE XYZ along the Luminance Y-axis to separate Luminance and Chrominance information.

To convert from CIE xyY to HEX or RGB (sRGB) you need to follow the following path:

CIE xyY --> CIE XYZ --> RGB --> HEX

Using Colour, this transformation would be expressed as follows:

import colour
xyY = [0.615, 0.346, 5.6]
XYZ = colour.xyY_to_XYZ(xyY)
RGB = colour.XYZ_to_sRGB(XYZ, apply_cctf_encoding=False)
print(RGB)
RGB_n = colour.utilities.normalise_maximum(RGB)
print(RGB_n)
print(colour.notation.RGB_to_HEX(colour.cctf_encoding(RGB_n)))

[ 23.33310243   0.88648      0.07921734]
[ 1.          0.03799238  0.00339506]
#fe360b

or using the Automatic Colour Conversion Graph as of latest develop branch:

import colour
xyY = [0.615, 0.346, 5.6]
print(colour.convert(xyY, 'CIE xyY', 'Hexadecimal'))

.../colour/colour/utilities/verbose.py:237: ColourUsageWarning: "RGB" array contains values over 1 and will be normalised, unpredictable results may occur!
  warn(*args, **kwargs)
#fe360b

Note that because your colour is High Dynamic Range (HDR), i.e. Y = 5.6, it cannot be converted to Hexadecimal representation without a normalisation process before converting from RGB to Hexadecimal. Here the colours are normalised so that the maximum RGB value is 1 but it is also worth considering that you are using sRGB colours and divide Y by 80 which is the typical sRGB display peak luminance.