CIE LAB anyone?

[edgework]

The method for removing the color cast comes from the chapter on LAB color in Dan Margulis' earlier book, Professional Photoshop. He seems to have abandoned this technique for the more intuitive approach he takes in his latest work, but I find it's an incredibly simple and powerful way to kill whatever cast you have.

The white of her dress is reading a:9, b:9. The black phone (front panel) is reading a:54, b:17. Right off we see that shadows and highlights will need a separate treatment. While RGB and CMYK allow curves that address different tonal ranges, the lightness channel in lab allows you to target highlight, shadows or midtones specifically, using blending options. I used one curve for the highlights, then placed an adjustment layer on top targeting the shadows. The approach is identical for both curves. I've included the second set of curves, as well as the blending settings.

Make sure that the light/dark gradient on the curve window has darks set at the left. (This is contrary to the method Dan uses in his LAB book, but it is necessary to match the Info readouts). Since the highlights read 9 in both color channels, the curve will be the same. Click somewhere in the midrange, and in the input/output windows, plug in the values; 9 for inupt, 0 for output. Do this for both a and b curves.

Now the highlights read 0 0 and the phone reads 47 9. So the second curve uses those values to address the shadow cast. Those are included below. Then, double clicking to the right of the layer name brings up the blending options window. Setting the channel to lightness, the settings shown will begin fading out the effects of this curve at the first white arrow and totally exclude it by the second arrow. These settings are intuitive and to some extent a judgement call. I was concerned that the drastic moves did not affect the highlights that the first curve had already fixed. The quartertones had been helped by that curve but still needed further moves. The fade-out was set to address both those needs.

The third curve is a straight color enhancement curve, as described in the early chapters of Dan's book. For this, I reversed the light/dark gradient. Note that the blending options emphasize the midtones, leaving the highlights and shadows, previously adjusted, intact. Note also that the curves do not move through the center point. Ordinarily this would cause the highlights and shadows to take on a serious cast, but the exclusion of the blending options prevents this from happening. I favored the green in the a curve and the yellow in the blue. The curve moves are pretty extreme, and so I set the opacity of this layer to 36%.

These settings are all variable, and a matter of judgement. Any number of modifications could produce a better result, I'm sure. But the approach, the ability to address highlights, shadows and midtones separately, while not unique to LAB, is much more effective when coupled with the power of it's cast killing curves.

What is obvious, now that there is some definition to the colors, is that this is one seriously messed up image. It's going to be impossible to address the rest of the issues without making some local selections. In addition to the green band at the right, the rug along the left side is also disastrous. Contrast sucks and dozens of other glitches show up. These could be addressed in LAB as well, but for this stuff, LAB doesn't offer much of an advantage over RGB or CMYK and for the local color moves, might not be as good. LAB is a battering ram. From here on, something more subtle would be called for.