DAA106 Imaging Concepts | Michael Martin
Color Correction by the Numbers
This photo has an unwanted yellow green color cast. Let’s correct the color using the tools in photoshop rather than just guessing.
You will need access to the Info and the Properties panels, so open those up (window menu). Choose the color sampler tool – it is underneath the eyedropper. Set the sample size to 3x3 or 5x5 average.
Click on a point in the photo that is nearly white, but not quite. There should be some slight tone to the area. Try to find a sample that you think should be neutral colored. I set a point in the not quite white area of the white truck hood. Click on a point that is nearly black, but not quite. There should be some photo information there. Try to find a sample that you think should be neutral colored. It may help to use caps lock so your color sampler tool turns into a cross hair and is easier to see the point. I set a point in the shadow on the dark gray pole.
Add a Levels Adjustment Layer. Look at the info panel. You can see the red, green, and blue values for color samples 1 and 2. You will notice that there are two sets of numbers for each point. The left is the original image and on the right of the slash is the levels adjustment layer. You will ignore the numbers to the left of the slashes.
Adjust the highlights (point 1) first. All three numbers should be the highest number. In this case, you will need to change the green and blue channels to 246. Click the color channel drop down in the adjustment layer and select the Red, Green, or Blue. Click in the highlight box to activate it, and use the up and down arrows to raise the value to the highest of the three. Ignore the properties panel and watch the numbers to the right of the slash in point 1 in the info panel.
Do the same for the shadow values (point 2), but set all three channels down to the lowest number. In this case, all three should be 30. Pull down the desired channel; click in the shadow box to activate it, and use the up and down arrows to equalize the three numbers. Again, ignore the properties panel and watch the number to the right of the slash in point 2 in the info panel.
Original image
Corrected. Warm yellow green haze is neutralized. Notice the improvement in the sky, the black pick up truck, and the dog on the right of the picture You sometimes have to adjust the overall levels after correcting color