Camera Raw "Tint" A hard question...I think

[Abitconfused]

Is Camera Raw Tint similar to the mired menu option of many digital cameras? And, why does using the eyedropper tool on a white balance card in Raw change the Tint value? How does Camera Raw determine what Tint value to use?

[revi]

White balance correction means adjusting the 3 colour channels Red, Green, and Blue, so that the reference point is neutral (i.e. all three channels have the same value). This means that to be able to fully correct white balance you need 2 independent variables (you can keep one channel fixed). In practice, colour temperature (in K) is used as one of the variables, and 'tint' is the other. The software (on computer or camera) will translate these values to corrections to red, green or blue channels. (You can find the math involved here and here)

This system has the advantage that (in practice) you can get away with adjusting only channel (colour temperature) when using only daylight or incandescent lighting (both so-called 'black-body' light sources, more or less). With film, that means only one range of filters (either in front of the lens, or in front of the extra lights when combining daylight and lamps).

Now that more and more lamps are of the fluorescent type (and this includes LEDs), we need the 'tint' (or 'green') adjustment as well.

Note that white-balance correction only takes into account the 'saturation' of the selected point, value/intensity can and often will change when adjusting white balance (i.e. the image will get lighter or darker when adjusting WB).

Remco

[Colin Southern]

Just to illuminate the topic from a different source (pun intended) ...

Our eyes "see" in RGB but our brain works in 2 colour opponent pairs; blue/yellow and green/magenta (or put another way, a colour can be described in terms of RGB values or LAB values (in LAB the L stands for a luminance value, and A & B stand for the 2 colour opponent pairs I've mentioned).

In practice, this means than an image with a colour cast will be either too warm or too cold (the "A" channel axis) or too green or magenta (the "B" channel axis). LAB makes it a lot easier to understand colour shifts whereas with RGB it's a LOT harder to create a shift unless it aligns perfectly with one of the primary channels.