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Color Correction by the numbers!

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#1 bobjarman


    Manta Ray

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Posted 10 June 2002 - 05:44 PM

For my milestone 100'th post, I thought I would share a tip I recently learned in photoshop.

Recently, Jay posted an image of a squid that was really quite a nice shot but had a definate green cast to it. I asked Jay if he would mind if I used his image to demonstrate a technique I learned recently about curves and color correction. He agreed, and shown below are the results of about 2 minutes worth of work. It's not yet perfect, but I thought I would demonstrate the power of the curves box in PS.

What I did was as follows:

1: Open an image and find a nuetral color in the image. Nuetral being defined as a black, grey or white. A color that on a monitor would be read as equal portions of Red/Green/Blue.

2: Chose that spot with your color sampler. (its located under the eyedropper in PS7)

3: Open up the info box and the curve box. In the image I used, the numbers for the spot I picked were very heavy in green and blue, and extremely light in red. (Makes sense at depth) The actual number information for the spot you selected will show in the info box.

4: The objective of what you are trying to do, assuming you have chosen a true neutral color is to make the red/blue/green numbers equal. To do this, chose one of the three color channels, and starting exactly at the middle, pull the curve to the top or bottom corner directly opposite the center point. Watch the info box as you do this, and you will see the number gorw or shrink. Repeat the process for the other two color channels until you are happy with the color of the image. Than click ok. Poof! instant correct color. Usually I try to raise the lowest number and lower the higest number to the middle value of the three colors.

Its not easy, as the neutral spot you pick will make a lot of difference in the finished product so try different areas. Plus you can pull the curve up or down to emphasize the darks or lights. If your not happy with the result, siimply go back and start again with a different color point.

5: Finally, often time the image will look a bit flat. If that happens. pull the curve box up again, and while in the RGB channel simply take the endpoints of the line and slide them both towards the center. I recommend trying the same amount on both the bottom left corner and the top right. Don't move them off the axis, just slide the starting point towards the center.

Ok....here is the result of about 2 minutes work. Jay had a neat image, it just needed color/contrast correction. So next time you got that green dull image....don't trash it on the surface....give this a try first!

I couldn't get a shot to upload so i put it into photo.net:


Added: The guy that told me about this procedure gave me the source. A really wonderful web site that does a lot better job of demonstrating this procedure than I probably did.


I glanced through all of his tutorials, they are quite good, but this one is a winner for underwater shooting!

[Edited on 6-11-2002 by bobjarman]