- Color Essentials
- Identifying a Color Cast
- Understanding Color Correction with Image Variations
- Mimicking the Color Darkroom with Color Balance
- Global Color Correction
- The Numbers Don't Lie
- Selective Color Correction
- Alleviating Extreme Color Problems
- Correcting Color Temperature Problems
- Interchannel Color Correction
- Closing Thoughts
Understanding Color Correction with Image Variations
If all this talk about identifying color casts is making your head spin, don't worry. Photoshop Variations (Image > Adjustments > Variations) is a very useful tool if you're just starting out or need a refresher on color correction. Variations is similar to the color ring-around chart that photographic printers have been using for years to see which way to move color when making a color print. The color correction part of Variations shows you six pictures, each representing one of the primary colors (red, green, blue, cyan, magenta, and yellow) opposite its counterpart (red to cyan, green to magenta, and blue to yellow), as shown in figure 4.5. For example, if you have an image with a blue color cast, clicking the yellow image would add yellow and remove the blue.
Notice how easy it is to see the color change in the more neutral areas, such as the water and the building, while the saturated red of my jacket barely changes at all. This illustrates how easy it is to see color casts in neutral and light areas and how near to impossible it is to see color shifts in saturated areas.
Next to the OK and Cancel buttons are radio buttons that you click to control which image area to affect: Shadows, Midtones, Highlights, or Saturation. When using Variations to do color correction, I recommend that you start with the midtones and then refine the highlights. The only problem with Variations is that it is not an Adjustment Layer, so your color correction is applied directly to the image pixels. To ensure that you don't alter original image data, always work either on a duplicate file or duplicate the Background layer.
The original image shown in figure 4.6 was taken indoors in fluorescent light with a digital camera that was set to daylight color balance, turning the image yellow-green. With a few clicks in Variations, the image is neutral and much more pleasing (see figure 4.7).
Figure 4.5 The Variations dialog box is a useful tool to identify color casts and offers you many options for color correction.
Figure 4.6 Before
Figure 4.7 After
Use the Eyedropper tool and the Info palette to measure an area in the image that should be neutral. Because you haven't seen this room, how can you know what the real color is? Use your visual memory of a similar scene and you can guess that the wall in the background could be white or at least a very light neutral color. Figure 4.8 shows the readout of 156 Red, 183 Green, 130 Blue.
Duplicate the Background layer. This will protect the original pixels while you experiment with Variations to do the color correction.
Select Image > Adjustments > Variations and click the Midtones radio button. To see how Variations applies the opposite color principle, move the strength slider under the Saturation radio button to the right as seen in figure 4.9.
To work subtly, move the strength slider toward Fine to reduce the strength of each change, as shown in figure 4.10. Click More Blue to reduce the yellow, and then click More Magenta to reduce the green component. To strengthen any changes, just click the same color image again. Variations updates the center image to reflect the current change.
Adding the blue and magenta into the midtones might make the image darker. You can offset this by clicking the Lighter image on the right side of the interface.
Finally, click the Highlight radio button and click More Magenta once or twice to take out the last vestige of the green color cast.
Click OK and compare the before and after images using (Cmd + Z) [Ctrl + Z] to undo and redo the Variations. Or toggle the visibility of the duplicated Background layer on and off to reveal the original Background layer.
You can also check the results with the Info palette as shown in figure 4.11, where the RGB readout is now 158, 162, 162, which is an acceptable neutral for a snapshot like this one.
Figure 4.8 Start by sampling an area you believe should be neutral and examining the color readout in the Info palette.
In relationship to the other colors, the much higher green readout in this example is a dead giveaway of a strong green color cast, and the low blue readout tells you that this image also has a yellow color cast. Properly adjusted, all three colors will be within one or two points of one another.
Figure 4.9 Moving the slider controls the strength of the Variations change.
Figure 4.10 Start your Variations color correction with the midtones.
When using Variations, you can undo all changes by clicking in the upper-left corner of the original image.
Figure 4.11 Check the neutral image areas with the Eyedropper and Info palette to double-check that the color cast has been removed.
Ron Hirsch, a retired engineer and reader of the first edition of this book, was kind and generous to send me an empirical analysis of Image Variations versus Photoshop Color Balance which explains how Image Variations results can be achieved with Color Balance. You can find this analysis as a PDF in the chapter 4 section of http://www.digitalretouch.org.