Color Cast Removal - Numero Tré

jjbongjjbong Major grinsPosts: 244Registered Users Major grins
edited March 27, 2011 in Grad School
I spent a lot of time working on this image before I got something reasonable. So I'm interested if anyone else can do as good or better with less work.

This is the basilica of San Paolo Fuori le Mura in Rome. Another example of being there at the wrong time of day for the shot. But you're where you are when you are.

So here's the original after a little bit of CR processing:


Challenges here:

1. Kill the blue cast in the darker parts of the image
2. Don't lose the color or the contrast in the upper right. This is a remarkably important part of the image, which wasn't apparent to me intially, but which you notice (as I did) when you lose the color or contrast.

Here's what I ended up doing.

1. In Camera RAW, I set the White Point on a darker part of the statue, and adjusted the Exposure and Black sliders to get a decent histogram. Pathfinder has the original RAW image.

2. Use the technique described here [thread=192120]Color Cast Removal[/thread] to kill the cast. This was fairly difficult, as I had to kill the blue in the columns without killing the colors in upper right or the sky. I ended up using these Blend-If sliders on the 50% Color inverted layer:


The problem is that the blue cast lives in a very narrow range of B values. Lower than that range, you find the upper right of the image. Higher than that range, you find the sky. Blend-If controls aren't too precise.
Fortunately, I could handle the sky by adding L sliders, as the sky is pretty much the only thing here that's really bright.


Unfortunately, this killed the colors in the upper right. I couldn't find a way with Blend-If not to do that, so I did a simple mask to eliminate the layer effect from that part of the image, using the polygonal lasso tool (a blunt instrument).

I usually avoid creating masks, as frequently the effects look too artificial, but that wasn't the case here, probably because of the earlier Blend_Ifs. Here's the result so far, which is just the result of cast removal:


3. Use the technique described here for images that have a dark component and a light component
[thread=185327]Change Exposure and Multiply[/thread]

In this case, the exposure adjustment was Gamma 1.60, one multiply layer with a layer mask from the background Green Channel, blurred 30 px.

4. Use the standard steps of the workflow described here
[thread=184713]Dan Margulis' Picture Postcard Workflow[/thread]

In this case, Curve the Green and Red channels in Luminosity mode to add contrast to the statue and the upper right without at the same time blowing out the light part of the statue base.
Shadow/Highlight (faded)
Extreme LAB curve at low opacity.
LAB AB curve to boost colors at low opacity.
Slight LAB L curve to further enhance the contrast of the statue.
HIRALOAM sharpening and done.

I was quite surprised at how many tries it took me to find something that was to my eye reasonable. I'd love to see other approaches.
John Bongiovanni
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