Dear community
The calculation of the hue angle has been attempted with positive values in the CIELab system, considering the formula: tan-1 ( b* / a*)
For example:
With a = 0.23, and b = 15.01, the hue angle value was calculated in 89.12.
However:
With a = - 1.8 and b = 5.54, the hue angle value was - 72.00.
This result was does not match with that provided by the colorimeter, which is 90.01.
Is there a mistake in the calculation?
Thank you very much in advance.
Hi, Andrés. If you are using CieLAB colour space with D65 Iluminant and 10 degrees Observer, the hue angle for a = -1.8 and b = 5.54 is 107,999 degrees.
The explanation:
The hue angle formula is not just one, but many, depending on which quadrant your colour is located (see figure attached). When "a" has a negative value and "b" has a positive value, the colour is located in quadrant II, so the hue angle formula is 180 + tan-1 ( b* / a*).
I got the figure and formula from https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1745-4557.1995.tb00377.x
Hope i aswered your question.
Dear Yanelis
Surely you did, I supposed that there were different equations depending on the quadrant. Now I think it is clearer.
I will take a look at the information.
Thank you very much.
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