I revisited this endeavor a few days ago, wondering if I could remove that terrible blue ring from around the Death Star explosion on the DVD version. I realize that this was "fixed" for the Blu-ray, but my thinking was that this blue ring was part of a systemic problem with the entire movie. Previous attempts to remove it with a global change had failed, or had pulled all blue from the movie. So I came up with a more surgical approach:
Starting over with an unaltered base movie layer, I pulled up the values of the green and red in the channel mixer, in order to blow out the luminance. The layer on top of that was set to saturation blending mode, meaning that the luminance and hue was carried over from the base layer, with the saturation of the blending layer. To this layer I brought the saturation down to zero, meaning that now I was left with an image that was black and white, but with no saturation and blown out luminance. Finally, a third and final layer was set to "Darker Color" blend mode and placed on top of this black and white image. Now because the blue and red tones are the result of oversaturation, bringing the saturation to zero in the second layer had the result of targeting the blown out tones and making them darker. When darker color was applied to the top layer, the oversaturated colors were erased, while keeping the overall color balance of the DVD:
There's still some blue remaining, but this is still much improved over the original. I checked some other scenes next, and found that R2 had become much less blue:
I thought that this couldn't be right until I went and checked it against the Mike Verta frame found elsewhere on this blog. Turns out that R2 is actually this shade of blue!
There are many improvements in many scenes, such as the hologram scenes:
There are some blown out reds in the film, such as when Leia is hiding from stormtroopers at the beginning, and these are brought under control as well with this change.
The one problem with this technique is that some of the highlights are messed up, but this technique is still a work in progress