- Sep 26, 2003
- 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
Global Color Correction
As you know by now, Photoshop often gives you three or more ways of reaching the same end result. Some people don't like this and believe that their way is the only way. Puh-leeze! Color correction is an art form that relies on your perception, experience, and interpretation of the image. With the following exercises, we'll use Levels and Curves to rescue some pretty sad photos from color cast fates worse than death.
Using Auto Color Correction
New in Photoshop 7 is a much-improved Auto Color Correction functionone that you can control to achieve some remarkable results. I am usually the first one to shy away from anything with the word "auto" or "magic" in its name. The new Auto Color Correction offers a number of controls with which you can get into the color balance ballpark quickly and easilyespecially when working with digital camera files. Once you understand how Auto Color Correction works, it can save you a lot of time. Note that I am not referring to the Auto Levels, Auto Contrast, or Auto Color menu commands in the Image > Adjustments menu. I don't recommend those commands at all because you have no control over the values Photoshop uses to calculate the changes, and worst of allyou are not working with an Image Adjustment layer.
Both the Levels and Curves dialog boxes have an Auto button. Clicking Auto will perform the default corrections, regardless of where you access it. Because the interface is smaller with Levels, I use this one because I can see more of the image and get identical results. Clicking Options brings up the Auto Color Correction Options interface (see figure 4.17). It is here that you can cycle through the types of corrections or influence which values Auto Color references.
Figure 4.17 The Auto Color Correction options can be set from either the Levels or the Curves dialog box.
The Auto Color Correction Options Interface has six settings that enable you to control how the color is affected:
Enhance Monochromatic Contrast: Photoshop clips all color channels at once, using identical values for each, making shadows darker and light areas brighter. This is the same as Image > Adjustments > Auto Contrast, or moving the shadow and highlight slider in Levels to where image information begins on the RGB or CYMK composite histogram.
Enhance Per Channel Contrast: Photoshop will adjust each channel separately. This is identical to moving the shadow and highlight sliders of the individual image channels to where the image information starts. This is how Image > Adjustments > Auto Levels works.
Find Dark & Light Colors: Photoshop uses the lightest and darkest pixels in an image for the Shadow and Highlight values. This is the same as Image > Adjustments > Auto Color and may or may not introduce unwanted color casts.
Snap Neutral Midtones: With this selected, Photoshop looks for a nearly neutral color in your image and then forces it to gray. Image > Adjustments > Auto Color uses this option.
Target Colors Clipping: Enter values here to tell Photoshop the percentage of tones to ignore. For example, entering 0.02% for both Shadows and Highlights will skip the brightest and darkest 0.02% before starting calculations. The default 0.5% value is too high. If you want calculations to be based on non-neutral colors, clicking a color swatch will open the Color Picker, where you can choose any color as the Shadow, Midtone, or Highlight target.
Save as Defaults: Clicking this tells Photoshop that these are the settings you want to use anytime you click the Auto button in Levels or Curves. Note: If you select this option, the Clipping value you enter will also be the new defaults for the Auto Levels, Auto Contrast, and Auto Color menu commands.
The Beauty Is in the Auto Details
Now that Adobe has added the ability to control the Auto Color Correction, I find myself adding a Levels or Curves Adjustment Layer and clicking through the options to see what is going to happen. Many times the results are very goodif I pay attention to the details.
To get the best results from Auto Color, start by checking Find Dark and Light Colors and Snap Neutral Midtones and making sure that Save as Defaults is checked. Don't worry if this ruins your image for now. By setting these as defaults, you're ensuring that Photoshop is starting with Auto Color when you click Auto in either Levels or Curves. Click OK. If making this change ruined your image, just choose Edit > Undo and the change to the image will be reversed, but the settings will be remembered.
To continue controlling how Auto Color works, reopen the interface to adjust the Target Colors Clipping values, which are both too high at .50% and will result in blocked up shadows and blown out highlights. Start by reducing the shadow value to 0 and using the up arrow on your keyboard to go up .01% at a time. Keep an eye on the image shadow and highlights; values lower than the default will create pleasant, open shadows with information and printable highlights that aren't pure paper white.
The midtone default of a perfectly neutral gray may or may not be the best choice for your images. In fact, the perfect neutral may be visually too cold. You can adjust the midtone, and best of all, as with the previous changed settings, the change is interactive.
In the image in figure 4.18, the model car is a bit flat and due to the tungsten light, the overall image is yellow. Adjusting the midtone solves the problem.
Figure 4.18 The neutral gray midtone default may not be the best choice.
Add a Levels Adjustment Layer and click Options, which in this case brings up the default settings described previously.
To reduce the yellow cast, I clicked the midtone color swatch in the RGB values, left the red and green alone at 128, and raised the blue values by 20 points (see figure 4.19).
You can achieve the same result by simply dragging the color picker circle within the color picker. Keep an eye on the image to see the effect. In this case, the yellow was minimized and as a bonus, the blue car became even bluer.
Figure 4.19 Adjusting the midtone by raising the blue value.
Crop Before Clicking Auto
Consider cropping your image before using Auto Color Correction. David Bryant sent me the example in figure 4.20, where he tried Auto Color Correction but was not happy with any of the results. It wasn't until he noticed and cropped out the narrow white border on the bottom and right edge of the print that the Auto Color Correction worked, as in figure 4.21.
Figure 4.20 Before
Figure 4.21 After
The portrait in figure 4.22 shows an unattractive color shift that is only too typical of color prints from the 1970s and 80s. Using our knowledge of Auto Color Correction, we can fix many of the overall color problems, as shown in figure 4.23.
Figure 4.22 Before
Figure 4.23 After
Crop the image to remove the white border. As figure 4.24 shows, you can rotate the Crop tool to straighten out the image while cropping. To rotate your crop, move the mouse about a quarter-inch to the outside of the corner handle. The mouse will change into a curved arrow that you can use to rotate the crop bounding box.
Add a Levels or Curves Adjustment Layer. In this example, I used Levels, because the dialog box is smaller and lets me see more of the image. Click Options to access the Auto Color Correction settings. You should see a change in your image as soon as Auto Color Correction Options pops up, and it's not a good change, as figure 4.25 sadly illustrates. The image is now much too contrasty and coldly blue.
Click through the three options. With this image, Enhance Channel Contrast with Snap Neutral Midtones is the most effective. Because the default Clipping values are too high, I changed them to 0.20%, which reduced the highlights on his lapel and maintained image detail (see figure 4.26).
Click OK to accept the Options settings and click OK on the Levels dialog box to commit the changes. Compare the image before and after Auto Color Correction by turning the Adjustment Layer visibility off and on.
Figure 4.24 Cropping and rotating the image before using Auto Color Correction.
Figure 4.25 Add a Levels Adjustment Layer and Click Options.
Figure 4.26 Changing the Option settings from the defaults can make a big difference.
All in all, explaining how to use Auto Color takes longer than actually making the changes to achieve good and quick results.
Color Correction with Levels Eyedroppers
Working with the Levels or Curves eyedroppers to define the one, two, or three neutral areas of white, gray, or black will often remove a bothersome color cast. Figure 4.27 shows a scene photographed with a Nikon D100 digital camera in the late afternoon in Helsinki, Finland. You'd never know it from the photograph, but the building exterior is actually snow white. With a few clicks in Levels, you can restore the gleaming white facade, as seen in figure 4.28. Please note: The color cast in this example is not typical of the Nikon cameras, rather it was my fault for taking the picture with the wrong camera settings while rushing around before sunset.
Figure 4.27 Before
Figure 4.28 After
Before using the Levels or Curves eyedroppers, define the white and black target colors as described in Chapter 2 "Improving Tone and Contrast." For printing to an inkjet printer, use the HSB scale and set the white target color to 96% brightness, or RGB 245, 245, 245, and click OK. Double-click the black eyedropper and set the shadow target color to 5% on the HSB scale, or RGB 12, 12, 12.
The first step is to identify the color cast. If you're working with a well-calibrated monitor and have a good sense for color, you'll see that the building is too yellow. If you're not sure about color or your monitor, use the Info palette. Set your Eyedropper to Sample 3 by 3 Average on the options bar, and look for something you know should or could be neutral. This image has large expanses of white, but every image will be different. When you position the Eyedropper over a neutral color, the Info palette will reveal the color cast (see figure 4.29). In this case, the very low blue value of 83 signifies that the image is very weak in blue, which translates to strong in yellow, so the image has a yellow color cast.
I added a Levels Adjustment Layer and selected the white eyedropper. I clicked the lightest part of the building to define a new white point. Clicking with the eyedropper not only redefines the pixels clicked to white; it also neutralizes them. In the Info palette, I noted that the values of red, green, and blue are equal, proving that I removed the color cast, as shown in figure 4.30. You should experiment to find the best neutral points. Try as many areas as you like. Each click of the eyedropper will re-examine and adjust the image all over again.
Next select the midtone eyedropper and click the shady side of the building, as shown in figure 4.32. If you think about it, a white building in the shade should be gray, so this is a good way to find a neutral midpoint.
On many images, correcting for the white point and midtone may be enough. However, on this image, I also selected the black eyedropper and used the darkest of the little windows to set the new black point (see figure 4.33).
After defining the white and black points, take a second look at the image. If the image looks too dark or too light, use the midtone slider to lighten (by moving the midtone slider to the left) or darken (by moving the slider to the right).
Figure 4.29 The values in the Info palette help you identify the color cast.
Figure 4.30 Using the Levels white eyedropper to define a new white point improves overall color and contrast.
(Option + drag) [Alt + drag] the Highlight slider to the left, as you see in figure 4.31. Photoshop will reveal where the true highlight is. In this image, I ignored the lightest areas in the specular highlights of the golden crosses and concentrated on the building as circled. This technique works for the shadow point as well.
Figure 4.31 Finding the highlight point of an image.
Figure 4.32 Using the Levels gray eyedropper to define a neutral midpoint removes even more of the color cast.
Figure 4.33 Using the black eyedropper on a black point improves image density. Notice that it makes the sky come to life!
Multiple Color Corrections with Levels
Often, pictures taken at the same time will share the same problems. Whether it was bad lighting, bad processing, bad storage, or simply bad luck, you can save time and effort by fixing one, then applying that same adjustment to the rest.
The images in figure 4.34 were all taken at the same event, and all suffer from the same unfortunate lighting. By using a Levels adjustment layer on one, then sharing that same adjustment layer with the others, I was able to fix all four, as seen in figure 4.35, without four times the work.
Figure 4.34 Before
Figure 4.35 After
First we need to adjust one of the images using the Auto Color Correction technique addressed previously. Add a Levels Adjustment Layer and click Auto. As figure 4.36 shows, the initial Auto Color setting is rather good, but we can still improve the image with one more click.
We have an ideal neutral reference source to work withthe white wall in the background. Notice how the right side is still slightly green? By clicking the wall with the gray Levels eyedropper, the last hint of the colorcast is removed as seen in figure 4.37.
Click OK to accept the image correction.
Without closing your corrected image, open another of the problem images and drag the adjustment layer from the corrected image onto the second image, as in figure 4.38. This applies the same correction to the new image.
Figure 4.36 Using only Auto Color.
Figure 4.37 Correcting the color by clicking on the white wall with the midtone eyedropper.
Figure 4.38 Dragging the adjustment layer to a new image.
Subtle Color and Exposure Improvement with Curves
Not all images have overwhelming or obvious color casts. In fact, some images require a delicate touch to remove the color cast and adjust exposure. In this example, the photograph is off just a bitmeaning that it is only slightly too dark and red (see figure 4.39) In this example, I set new black, white, and gray points and improved the exposure with a Curves Adjustment Layer, and then fine-tuned the overall saturation with a Hue/Saturation Adjustment Layer. These changes, shown in figure 4.40, enable you to appreciate the beauty of the young woman.
Figure 4.39 Before
Figure 4.40 After
Add a Curves Adjustment Layer. Use the white eyedropper to set the wall just above her flower to white, the black eyedropper to set the shadow beneath her chin to black, and the gray eyedropper to set the wall in the upper left as neutral gray (see figure 4.41).
Boost the shadows and midtones by dragging the center of the curve upward to lighten the image and add the sparkle of a well-exposed photograph (see figure 4.42). Be careful to monitor the highlights on the girl's skin and flower in the Info palette so they are not forced to pure white.
Not all portraits require the following step, but in this instance the teenager's tanned arms are over saturated and visually distracting. To reduce the saturation, I added a Hue/ Saturation Adjustment Layer and decreased the overall saturation by 25, as seen in figure 4.43.
Figure 4.41 Setting new white, black, and gray points using the Curves eyedropper.
Figure 4.42 Lighten the image with Curves.
Using the gradient tool set to default black and white, I drew a gradient on the Hue/Saturation layer mask to shield the face from the desaturation, as shown in figure 4.44.
Figure 4.43 Decreasing the saturation reduces the heavy orange cast.
Figure 4.44 Taking advantage of the layer mask to control where the change takes place.
Using Curves with Luminosity
In most cases, using the target eyedroppers in Levels or Curves is an excellent method for removing color casts and adjust image contrast. But as with all good things, sometimes they do add unwanted density or saturation. To avoid the unwanted punch, combine the power of a Levels or Curves Adjustment Layer with the Luminosity Blending Mode, as shown in figures 4.45 and 4.46.
Figure 4.45 Before
Figure 4.46 After
I used the Curves black, gray, and white eyedroppers on the areas indicated in figure 4.47 and opened up the exposure with one Curves adjustment. This added too much false saturation to the clay pot.
Changing the Blending Mode of the Curves Adjustment Layer to Luminosity as seen in figure 4.48 offsets the unwanted saturation while maintaining the neutral tonal values. Toggle the Blending Mode from Luminosity to Normal to appreciate the difference.
Figure 4.47 Using eyedroppers and a Curves adjustment makes the image too saturated.
Figure 4.48 Changing the Adjustment Layer Blending Mode to Luminosity lessens the false saturation.