Adobe 23101335 User Guide - Page 338
Using channels to modify GIF lossiness, In the Modify Lossiness Setting dialog box
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328 CHAPTER 12 Optimizing Images for the Web To use a channel to modify JPEG quality: 1 In the Optimize panel/palette, choose a JPEG setting from the Settings menu, or choose JPEG from the file format menu. 2 Click the channel button ( ) to the right of the Quality text box. 3 In the Modify Quality Setting dialog box, choose the desired channel from the Channel menu. In ImageReady, you can choose Save Selection to create a new alpha channel based on the current selection. 4 To preview the results of the weighted optimization, select the Preview option. 5 Define the quality range: • To set the highest level of quality, drag the right (white) tab on the slider, enter a value in the Maximum text box, or use the arrows to change the current value. • To set the lowest level of quality, drag the left (black) tab on the slider, enter a value in the Minimum text box, or use the arrows to change the current value. 6 Click OK. Using channels to modify GIF lossiness When you use an alpha channel to optimize the amount of lossiness (or quality reduction) in a GIF image, white areas of the mask yield the highest quality, and black areas of the mask yield the lowest quality. You can adjust the maximum and minimum level of quality reduction in the Modify Lossiness Setting dialog box. To use a channel to modify GIF lossiness: 1 In the Optimize panel/palette, choose a GIF setting from the Settings menu, or choose GIF from the file format menu. 2 Click the channel button ( ) to the right of the Lossy text box. 3 In the Modify Lossiness Setting dialog box, choose the desired channel from the Channel menu. In ImageReady, you can choose Save Selection to create a new alpha channel based on the current selection. 4 To preview the results of the weighted optimization, select the Preview option. 5 Define the quality range: • To set the highest level of quality, drag the left (white) tab on the slider, enter a value in the Minimum text box, or use the arrows to change the current value. • To set the lowest level of quality, drag the right (black) tab on the slider, enter a value in the Maximum text box, or use the arrows to change the current value. Note: Lossiness is a reduction in quality; therefore, the highest level of image quality is defined by the Minimum value, and the lowest level of image quality is defined by the Maximum value. This is the opposite of the JPEG quality setting. 6 Click OK.
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