Correcting blue from shooting through tinted glass

[kirbinster]

My dad recently took a bunch of pictures from inside a tour bus. Some of them had a strange color cast from shooting through the glass. Others were even worse as they had a dark blue band at the top of the shots as the windows had a heavy dark blue tint at the top and then just slight blueing in the rest of the shots. I fixed this fairly well in lightroom with a two step process. The first was to select a custom white balance to remove the bulk of the tint.

The second correction I did I stumbled on by accident and would appreciate if someone might be able to explain to me why it works. I know it works, but am not sure why.

What I did was apply a graduated filter over the top of the blue with no correction other than making the graduation dark red. For some reason this red cancelled out the blue. Why does this work?????

A before / after is attached below.

[ArmySoldier777]

This is just my guess, but I did an explanation for someone else when dealing with blue haze, that I believe might be similar.

On my screen, I see the slightest hint of green in the blue, barely noticeable, but I can tell it's there behind the blue. So when you add red, you're completing the light spectrum with all 3 colors RGB, effectively making the lighting white. I might be wrong, but from personal experience that's what I've been able to figure out.

[Doug Pardee]

It works — sort-of — because the blue tint reduced the amount of red and green getting through the window. The reason that it's "sort-of" is that you're only fixing the red, not the green.

What you should be using is yellow rather than red; yellow is the opposite of blue. That should reduce the violet tones in the clouds and make your greens a bit more vibrant.

[ArmySoldier777]

Originally Posted by Doug Pardee

It works — sort-of — because the blue tint reduced the amount of red and green getting through the window. The reason that it's "sort-of" is that you're only fixing the red, not the green.

What you should be using is yellow rather than red; yellow is the opposite of blue. That should reduce the violet tones in the clouds and make your greens a bit more vibrant.

He's only applying it in a gradient to the areas affected by the tint though. It's not being applied to the whole image, So he doesn't really need to worry about getting vibrant greens. And applying yellow to what's already Blue/Green is going to also make the blue tint a vibrant green, not neutralize it.

I think he went about it the right way. Both blue and green are already there in the clouds, red is the only part of the light spectrum that isn't present. By adding it, he neutralized the the tint to create normal lighting. If the green hadn't already been there, he would've needed to do the same thing with a very subtle green gradient to complete the spectrum.

A similar effect could have been achieved by masking the part of the image and using the curves adjustment to lower the blue color channel.

[sk66]

What you did is a variance of the average blur/invert layer for color correction.

Which is good because the "average" wouldn't work for this image.