Adobe 23101335 User Guide - Page 337

ADOBE PHOTOSHOP 6.0 327 User Guide • Choose Regenerate from the Optimize palette menu. Note: Manually optimizing an image does not turn auto-regeneration on. The Regenerate option is available only when the optimized image is out of date (when Auto Regenerate is turned off and the image or its optimization settings are modified, or when optimization has been canceled). To cancel optimization: Click the Stop button next to the progress bar at the bottom of the image window. Using weighted optimization Weighted optimization lets you smoothly vary optimization settings across an image using an alpha channel. This technique produces higherquality results in critical image areas without sacrificing file size. With weighted optimization, you can produce gradual variations in GIF dithering, lossy GIF settings, and JPEG compression. Weighted optimization also lets you favor colors in selected image areas when you generate a color table. About alpha channels and weighted optimization Alpha channels lets you store selections as grayscale images called masks. In a mask, selected areas appear white, deselected areas appear black, and partially selected areas appear as shades of gray. When you use an alpha channel to apply optimization settings, the white areas of the mask describe the highest level of image quality, while the black areas for the mask describe the lowest level of image quality. (The level of optimization in gray areas of the mask decreases by a linear scale.) Weighted optimization is available for specific settings in the Optimize panel/palette, as indicated by the channel button ( ). This button has a dark background ( ) when a channel is selected and appears dimmed ( ) when no channels are available. To access the weighted optimization dialog box, simply click the channel button. To create a channel for use during optimization: Do one of the following: • (Photoshop) Save a selection as a mask, or create a new alpha channel and use the painting and editing tools to modify it. (See "Storing masks in alpha channels" on page 199.) • (ImageReady) Use a selection tool to select an area of the image. Either save the selection using the Select > Save Selection command, or choose the Save Selection command from the Channel pop-up menu in the weighted optimization dialog box. Using channels to modify JPEG quality When you use an alpha channel to optimize the range of quality in a JPEG 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 in the Modify Quality Setting dialog box.