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Using curves for color correction

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  #1  
Old 09-05-2001, 02:55 PM
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Question Using curves for color correction

I'm trying to follow along with a tutorial on color correcting images using curves. The RGB image they used as an example had a yellow cast so what they did was go to the blue channel in the curves dialog box and make adjustments there since blue is the complement to yellow.So far so good.Now I want to correct an image of my own which has a strong red cast. Earlier in the chapter they say to reduce red you either remove yellow and magenta or add cyan its complement. Since in the curves dialog box the only channels I have available are the red,green or blue I guess I have to do the correction somewhere else.I know I can use variations but I want to do the correction myself.In this instance, should I be using the selective color or the hue/saturation box to reduce the redtone ? I have a feeling I'm missing or confusing something. Thanks. Paulette
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Old 09-05-2001, 03:23 PM
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Paulette,

I'm no expert in this, but in RGB mode, the complementing colors are:
Red - Cyan
Green - Magenta
Blue - Yellow

So, if I wanted to use curves to remove a red cast, I would work on the red channel and increase the cyan. (If you're curve box is set the same way as mine, that would be moving points on the curve UP.) Similarly, if you want to remove yellow, work on the blue channel; to remove magenta, work on the green channel.

Don't know if that makes any sense, but I think that's what the tutorial is talking about.

And just for the record, I'm still not good enough with curves to get the color balancing effects I want. Perhaps it's because I understand it all wrong? If so, I'm sure someone will correct me.

Jeanie
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Old 09-05-2001, 04:46 PM
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Jeanie
You said it correctly. By lowering your red in curves you are increasing your cyan. Look at color balance under image adjust and you will see the same principal laid out. Red is to the right of cyan at the top line so by moving the slider either way you are adding or decreasing one color to make the opposite color more prevelant. It's the same thing in curves except you don't see the the word cyan written at the top with red. Sure gets confusing sometimes hey?
DJ
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Old 09-05-2001, 05:03 PM
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Thank you for ther information.I really want to learn to do things the correct way and not just "wing" it.I'll give it a try and get back.So much to learn!PC
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Old 09-05-2001, 05:44 PM
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What do you mean not wing it? That was the method used to answer your question.
DJ
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Old 09-05-2001, 06:48 PM
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Nevertheless the answer was a good one! Okay I returned to the drawing board and messed around with the color channels and their opposites. I think that the relationships are starting to sink in. Anyway, one thing which I did which made a big difference was to click the white and black points on the image. Also I couldn't resist adding some color back in. I'm trying to start work on my midterm project which has to be an ad representing ones' work. I'll probably do something along these lines but I think I can come up with something better. PC
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Old 09-05-2001, 06:49 PM
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picture in question
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File Type: jpg family.jpg (88.3 KB, 48 views)
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Old 09-05-2001, 10:25 PM
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Thumbs down

Paulette
Great job! Looks like you figured out those colors pretty well from the photos of before and after.
Let us know what your midterm project turns out like. I think it will be neat to see what you come up with, you definately have the talent.
DJ
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Old 09-05-2001, 10:54 PM
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Paulette,

I'd say you've got the hang of working with color channels! Great job on that photo!

Think about submitting your "ad" to the business challenge! (Thread is in the work/jobs forum.) I'm still working on mine, but there have been a few entries already. The more the merrier!

Jeanie
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