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Removing colour cast

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  #1  
Old 09-23-2004, 06:16 PM
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Conk Conk is offline
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Removing colour cast

I would like to find out the best way of removing colour cast from subjects after shooting against a chromakey green backdrop. I'm using Photoshop CS.
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Old 09-23-2004, 06:21 PM
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Doug Nelson Doug Nelson is offline
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If there's green reflected on the subject from the greenscreen, the purpose of the greenscreen has been defeated. Not that this helps you now
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Old 09-23-2004, 06:29 PM
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Hi Colin,

You could try these great ways for minimizing/removing your colour cast:

Quick Fix for Severe Colorcast

Another Quick Fix for Unwanted Color Cast

Quick color cast correction

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Old 09-23-2004, 06:37 PM
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Thank you very much Flora. The colour cast I'm getting isn't as near severe as the examples I've seen in those tutorials but should do the trick. It is just like an inner fringing in small areas of my subjects. I've been able to reduce it enough that I can print an image and it looks fine but when viewed in the sunlight, all the defects jump out, such as the green cast.
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Old 09-23-2004, 07:40 PM
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Hi Colin,

glad I could help!

But if you are still not satisfied with the result ... if possible, you could post the image or part of it ....

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Old 09-23-2004, 09:03 PM
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Chip Hildreth Chip Hildreth is offline
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Sounds like the problem Doug described. I've had it with a chromakey blue BG.

If the subject is too close to the background you get reflected light from it that diffracts around the subject... makes the colored fringe you describe. It's also a problem if they are standing on colored seamless paper but the reflections drop off before somewhere below knee level in most situations.

It gets down to distance from the reflection source. You want the reflections to fall off (inverse square law thing) before they reach and register on the subject. You can use white reflectors to backfill areas where the mainlight doesn't overpower the reflections.

For future shoots you can put some space between the subject and the BG. I've had better luck suppressing the BG reflections by lighting the paper above the subject's head with a single, bare bulb strobe placed close to it. I've gone to a white BG lit the same way when I need to knock the subject out... selection in PS is a lot more controllable as long as there is good lighting contrast between subject and BG.

chip
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Old 09-24-2004, 12:36 AM
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Thanks chip. I have tried moving the subject away from the bg but maybe not enough. I also think that moving my lighting a bit closer to my subject and try not to light the bg so much.

Flora, I didn't post an image because the colour cast isn't as visible when displaying it at a low resolution web displsay. It is important that it doesn't show up on my prints. I've yet to try the tutorials but will be posting as soon as I get a chance. Thanks again.
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Old 09-24-2004, 02:17 AM
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Colin, Sounds like you have things in hand, but you could just post a cropped patch of the photo showing the problem at full resolution, rather than the whole thing at lower resolution.
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Old 09-24-2004, 10:57 AM
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Slept on it and I have a couple of minor ideas.

Is the fringe in places like (assuming human subjects) the armpits, between fingers, under ears, etc.? If so, your reflections are probably coming from below. You can feather your mainlight and reflectors to illuminate the subject only and miss the BG underneath them. Overpowering them by moving the mainlight closer will work but then you get the falloff problem where there is three stops of range from nose to ear... you know what I'm talking about.
You could also throw a fill light in from below but if it's off center you still have problems in the nooks and crannies on the shadow side... plus, you probably don't want to use lots of lights.
You might try black masking any BG material that isn't in the photo if the subject is relatively stationary just to suppress all the colored light flying around the room.
Another question... what's the purpose of the chromakey green?

Aside, I checked your website; the portraits are nice. I've not done any dog photography but regularly do retouching on show dogs for ads; it's fun work.
It's the aircraft I really like though; I used to be into aerobatics in a big way, owned a Pitts S1S... sold it about eight years ago and haven't flown since.
The shots are just like what you see in 'Aerobatics Today' and airshow galleries... very cool. I like the Sukhoi.

Good luck.

Chip
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Old 10-25-2004, 11:22 PM
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Well, I'm still having a problem removing this cast and thought I'd post an image that clearly shows the green cast on the dogs front leg. If you look close enough it is also apparent in other area's.
After I replace the background with another digital image, the green cast is visible in areas on the dog. This image shows the dog lying on the chroma key backdrop but most of my images just have the animal on a table using the Chromakey in the background and not beneath. I just used this image as an example of the colour cast.
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File Type: jpg cast 1.jpg (52.5 KB, 33 views)
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