Tutorial 3

How to remove color casts

Color casts occur when the Red, Green, and Blue channels are not balanced. In this tutorial, we will show you how to remove color casts from an image.

Before:

After:

To remove color casts, you should have one color as the reference color and know what it should be so you can make corrections to this color along with the other colors to remove color casts. For example, if the stripes are supposed to be red but they are not shown as red in an image. You can use the stripe as the reference color and make corrections to it so that it is shown as red.

In this tutorial, we use Figure 10.03.1 as the original image with color casts. You may right click and save this image to your disk, then open it in Image Broadway if you want to practice it yourself while following the tutorial steps below. You may also right click on this image and copy it to the Clipboard and use the Image Broadway File > Clipboard menu to paste it in as a new image. Optionally, you may click the Navigator tab to display the Navigator window and use its slider bar to zoom in and out; or you may click the Info tab to display the exact pixel color and cursor information in the Info window.

   
   Figure 10.03.1

1. Use the Adjust/Enhance > Color > Curves menu to open the Curves dialog box.

      
      Figure 10.03.2

2. Click the Info tab to display the Info window. Click near the center shrub in the image to pick up a reference color with its original RGB values close to (193, 179, 184) but supposed be (179, 179, 179) after the correction. In the Info window, you may see these numbers displayed. If you select a different point in the image, these values may vary.

3. Click the cross point of the curve and the vertical line in the Curve dialog box to mark it as the control point.

4. You will be moving 193 to 179 and 184 to 179 in their respective channels. In Figure 10.03.3, you can drag to move the red channel cross point along the vertical line until you see "x193y179". In Figure 10.03.3b, you can drag to move the blue channel middle point until you see "x184y179".

   
   Figure 10.03.3

   
   Figure 10.03.3b

5. You can repeat the same method to additional points in the image to remove other color casts from the image.

   
   Figure 10.03.4