Archive for June, 2009

Removing Color Cast

June 7, 20090 Comments

I’m always looking for new ways to remove color cast from images. Sometimes the color cast can be very dramatic and sometimes very subtle, depending on light conditions, camera white balance, etc. Most of the time our eyes tend to compensate for the color cast, unless it is extreme. There are many ways to eliminate color cast at the time the photo is taken, you can use a gray card, set a custom white balance in the camera using something white or neutral, like an Expodisc, or even a sheet of white paper. Most of the time I use the white balance presets on the camera, for example, tungsten, flash or shady. The presets usually do a relatively good job removing the color cast, but not all.

Today I discovered a new way in Photoshop to remove the remaining color cast that the camera doesn’t when using the white balance setting on the camera. I can’t remember where I read about the method on the web, but it seems to work great.

Steps:

Open the image you would like to modify and create a new layer.

You should now have the background layer and the empty new layer.

Photoshop layer1

Fill the new layer with 50% gray and set the blending mode to Difference. You photo will look something like a negative.

Photoshop layers

Now using the eyedropper tool, find the darkest black you can find. I find looking at the RGB values in the Info tab helps find the blackest black, or something close. A RGB value of 0,0,0 would be devoid of all color. Hold the shift key and click on this spot. You should see a target if you’ve done this correctly. I’ve drawn a red box around the target in my photo.

Photoshop difference layer

Now, discard the 50% gray layer.

Add a levels adjustment layer and select the gray eyedropper to set the gray point for the image. It may make it easier to set the “Caps Lock” to change the eyedropper tool to a target. You want to click on the exact pixel you chose above, then click OK.

Photoshop levels adjustment

Now the color-cast should be removed.

Here is a photo I took a while ago in Vienna, I removed a slight blue color cast.

Before:

Vienna bike rental image (before)

After:

Vienna bike rental image (after)

Until next time – Jim

** Just wanted to let you know I found the person that originally created this process, Dave Cross. Dave has a great blog that I highly recommend. http://davecross.blogspot.com/.

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