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Unit of "tint" in Adobe Camera Raw?

Doug Kerr

Well-known member
In Adobe Camera Way (the raw file management accessory to Adobe Photoshop), we are given the opportunity to apply a color correction (that is, compensation for the chromaticity of the ambient light not being that of the color space reference white), or to observe the color correction "vector" the camera would apply in preparing the image for JPG output.

The color correction vector is described by two parameters, labeled "color temperature" and "tint". Certainly "color temperature" actually means "correlated color temperature" (CCT), since only certain chromaticities (those lying on the so-called Planckian, or "blackbody", locus on a CIE chromaticity diagram) have an actual color temperature.

"Tint" presumably means the amount by which the chromaticity being described lies off the locus; that is, differs from the blackbody chromaticity whose color temperature is cited as the "correlated color temperature" description of the chromaticity being described.

In scientific work, this departure is often called "delta uv", since it is reckoned on the CIE "u-v" chromaticity diagram (not the familiar "x-y" diagram), and its unit is normally the unit of u and v (a very large unit, since u and v have ranges of only about 0.5 unit across the whole visible part of the diagram).

Thus, a typical delta uv value (perhaps for a chromaticity such as "illuminant D65", the reference white chromaticity of the sRGB color space) might be on the order of 0.002 uv unit.

Clearly, this is not the unit of "tint" in Adobe Camera Raw.

Does anyone here know the unit used for "tint", or anything more about how it is actually defined ?

Thanks.
 
Last edited:

Andrew Rodney

New member
Does anyone here know the unit used for "tint", or anything more about how it is actually defined ?
According to Thomas Knoll, Tint is the offset distance from the black body curve in uv space (times a constant of 3000 to make the units human friendly).
 

Doug Kerr

Well-known member
Hi, Andrew,

According to Thomas Knoll, Tint is the offset distance from the black body curve in uv space (times a constant of 3000 to make the units human friendly).
Just what I needed to know. Thanks so much (and to Mr. Knoll, as well).

I don't have an authentic value for the delta uv ("duv") of D65, but looking at some graphic plots that had a scale of duv, it looks to be perhaps +0.002 uv units. That would reckon as a "tint" of about +6 tint units.

Best regards,

Doug
 
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