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original brightness value.
Figure 17-2: An image before the advent of the Invert command (left) and after (right).Note By itself, the Invert command is not sufficient to convert a scanned color photographic negative to a positive. Negative film produces an orange cast that the Invert command does not address. After inverting, you can use the Variations command to remove the color cast. Or avoid Invert altogether and use the Levels command to invert the image. Both Variations and Levels are explained later in this chapter.
Image® Adjustments® Invert is just about the only color-mapping command that retains the rich diversity of color in an image. (The Hue/Saturation command also retains color diversity under specific conditions.) For example, if you apply the Invert command twice in a row, you arrive at your original
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Part V: Color and Output
image without any loss in quality.
When youre working on a full-color image, the Invert command simply inverts the contents of each color channel. This means the command produces very different results when applied to RGB, Lab, and especially CMYK images. Typically, the Invert command changes most pixels in a CMYK image to black. Except in rare instances such as in night scenes the black channel contains lots of light shades and few dark shades. So when you invert the channel, it becomes extremely dark.Note Just so you know, when I refer to applying color corrections in the CMYK mode, I mean applying them after choosing Image® Mode® CMYK Color. Applying corrections in the RGB mode when View® Proof Setup® Working CMYK is active produces the same effect as when Working CMYK is not selected. The only difference is that the on-screen colors are curtailed slightly to fit inside the CMYK color space. Youre still editing inside the same old red, green, and blue color channels, so the effects are the same.Tip
As I mentioned back in Chapter 12, inverting the contents of the mask channel is the same as applying Select® Inverse to a selection outline in the marching ants mode. In fact, this is one of the most useful applications of the filter. Equalize
Equalize is the smartest and at the same time least useful of the Image® Adjustments pack. When you invoke this command, Photoshop searches for the lightest and darkest color values in a selection.
Then it maps the lightest color in all the color channels to white, maps the darkest color in the channels to black, and distributes the remaining colors to other brightness levels in an effort to evenly distribute pixels over the entire brightness spectrum. This doesnt mean that any one pixel will actually appear white or black after you apply Equalize. Rather, one pixel in at least one channel will be white and another pixel in at least one channel will be black. In an RGB image, for example, the red, green, or blue component of one pixel would be white, but the other two components of that same pixel might be black. The result is a higher contrast image with white and black pixels scattered throughout the color channels.
If no portion of the image is selected when you choose Image® Adjustments®Equalize, Photoshop automatically maps the entire image across the brightness spectrum, as shown in the upper-right example of Figure 17-3. If you select a portion of the image before choosing the Equalize command, however, Photoshop displays a dialog box containing the following two radio
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563 Photoshop CS Bible @Team LiB
Figure 17-3: An image before (top left) and after (top right) applying the Equalize command when no portion of the image is selected. You can also use the brightness values in a selected region as the basis for equalizing an entire image (bottom left and right).
Equalize Selected Area Only: Select this option to apply the Equalize command strictly within the confines of the selection. The lightest pixel in the selection becomes white, the darkest pixel becomes black, and the others remap to shades in between.
Equalize Entire Image Based on Selected Area: If you select the second radio button, which is the default setting, Photoshop applies the Equalize command to the entire image based on the lightest and darkest colors in the selection. All colors in the image that are lighter than the lightest color in the selection become white and all colors darker than the darkest color in the selection become black.
The bottom two examples in Figure 17-3 show the effects of selecting different parts of the image when the Equalize Entire Image Based on Selected Area option is in force. In the left example, I selected a portion of the image with both light and dark values, which boosted the amount of contrast between highlights and shadows in the image. In many ways, the result is better than the overall adjustment in the upper-right example. In the bottom-right example, I selected a predominantly lighter area, which resulted in an over-darkening of the entire image.