Adobe Photoshop CS5 for Photographers - Martin Evening [159]
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Here is an example of the Curves adjustment that was made to the three channels based on the Info panel information. The first RGB readout figure indicates the original input value. At each point I looked at the three numbers to see which of these represented the median value. I then adjusted the points in the other two channels so that these other two output values matched the median value (you can manually drag the point or use the keyboard arrows to balance the output value to match those of the other two channels). Note that +arrow key moves the control points in multiples of 10.
Hue/Saturation
The Hue/Saturation dialog controls are based around the HSB (Hue, Saturation, Brightness) color model, which is basically an intuitive form of the Lab Color model. When you select the Hue/Saturation image adjustment you can adjust the image colors globally, or you can selectively apply an adjustment to a narrower range of colors. The two color spectrum ramps at the bottom of the Hue/Saturation dialog box provide a visual clue as to how the colors are being mapped from one color to another. These hue values are based on a 360 degree spectrum, where red is positioned mid-slider at 0 degrees and all the other colors are assigned numeric values in relation to this. So cyan (the complementary color of red) can be found at either −180 or +180 degrees. Adjusting the Hue slider alters the way colors in the image are mapped to new color values and Figure 5.51 shows an extreme example of how the colors in a normal color image would look if they were mapped by a strong Hue adjustment. As the Hue slider is moved you will notice that the lower color ramp position slides left or right, relative to the upper color ramp.
Figure 5.51 This shows an extreme example of how a Hue/Saturation adjustment can be used to radically alter the appearance of a photograph. As you move the Hue slider left or right the colors in the image are mapped to new values. You get an indication of this transformation by looking at the two color ramps at the bottom of the dialog. The top one represents the original ‘input’ color spectrum and the lower ramp represents how those colors are translated as output colors.
Saturation adjustments are easy enough to understand. A positive value boosts the color saturation, while a negative value reduces the saturation in an image. Outside the Master edit mode, you can choose from one of six preset color ranges with which to narrow the focus of a Hue/Saturation adjustment. Once you have selected one of these color range options, you can then sample a new color value from the image window, and this centers the Hue/Saturation adjustments around the sampled color. Use a -click in the image area to add to the color selection and an -click to subtract colors (see page 354). As I have mentioned a few times already, there is now an ‘Auto-Select Targeted Adjustment Tool’ Adjustment panel option that automatically selects the target adjustment tool when the adjustment layer is made active. In the case of the Hue Saturation adjustment it automatically selects the Saturation slider and targets the appropriate color range.
When the Colorize option is checked, the hue component of the image is replaced with red (Hue value 0 degrees), Lightness remains the same at 0% and Saturation at 25%. You could use this to colorize a monochrome image, but you are better off using the Photo Filter adjustment to do this (see page 356).
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This shows a portrait photograph in which I wanted to target the purple background color and make it less intense. One approach would be to go to the target color group menu shown here and select ‘Magentas’.
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Another method was to make the target adjustment tool active (circled) and carry out an on-image adjustment by