L*a*b* color : Problem with the Luminance value

[muks]

Thanx mathan.

[ElRambo]

Hi,

This is expected behavior. Presumably the value is internally calculated on a 0-100 basis. However, on page 15-34 of the Vision Concepts Manual (July 2007) regarding CIE L*a*b* color conversion, it gives the following:

"NI Vision normalizes the result of the L* transformation to range from 0 to 255."

I am assuming this normalization is a linear scaling factor of 255/100, transforming the values from a [0-100] range to a [0-255] range. My guess is that this is done to give greater dynamic range when representing the L* value with just one byte.

Regards,

[chilly_charly]

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Maxime MULLER a écrit:

Hi,

This is expected behavior. Presumably the value is internally calculated on a 0-100 basis. However, on page 15-34 of the Vision Concepts Manual (July 2007) regarding CIE L*a*b* color conversion, it gives the following:

"NI Vision normalizes the result of the L* transformation to range from 0 to 255."

I am assuming this normalization is a linear scaling factor of 255/100, transforming the values from a [0-100] range to a [0-255] range. My guess is that this is done to give greater dynamic range when representing the L* value with just one byte.

Regards,

---

Thanks for the search, Maxime.
As a matter of fact, the L* value returned by the vi is not coded as a U8, but as a Dble. Therefore the 0-255 range does not increase the dynamic range. And most color measuring devices return L* values in the 0-100 range. Clearly something as do be done. Should we advise the "Compagnie Internationale de l'Eclairage"(CIE) that their definition should be changed, or can we expect NI vision to follow more closely international standards in a near future ? 😉

[Ben]

CC,

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Ben

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