Adobe 23101335 User Guide - Page 330
Optimizing images, About PNG-24 format, Viewing optimization options
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320 CHAPTER 12 Optimizing Images for the Web As with the GIF format, you can reduce the number of colors in the image and choose options to control the way colors dither in the application or in the browser. The PNG-8 format supports background transparency and background matting, in which you blend the edges of the image with a Web page background color. PNG-8 with 0% dither, and with 100% dither 256 levels of transparency to blend the edges of an image smoothly with any background color. However, multilevel transparency is not supported by all browsers. Optimizing images To optimize an image for the Web, you select a file format and other options in the Optimize panel (Photoshop) or the Optimize palette (ImageReady). You can apply different optimization settings to different slices in an image. You can also use alpha channels to selectively optimize an image within a slice or across slice boundaries. About PNG-24 format The PNG-24 format supports 24-bit color. Like the JPEG format, PNG-24 preserves the broad range and subtle variations in brightness and hue found in photographs. Like the GIF and PNG-8 formats, PNG-24 preserves sharp detail, such as that in line art, logos, or illustrations with type. The PNG-24 format uses the same lossless compression method as the PNG-8 format. For that reason, PNG-24 files are usually larger than JPEG files of the same image. PNG-24 browser support is similar to that for PNG-8. In addition to supporting background transparency and background matting, the PNG-24 format supports multilevel transparency. Multilevel transparency allows you to preserve up to Viewing optimization options Optimization options appear in the Optimize panel (Photoshop) and the Optimize palette (ImageReady). These options vary depending on the file format you select. To view the Optimize panel/palette: Do one of the following: • (Photoshop) Choose File > Save for Web. The Optimize panel is displayed on the right side of the dialog box, beneath the Output Settings button. • (ImageReady) Choose View > Show Optimize or click the Optimize palette tab. To show all the optimization options, click the Show Options control ( ) on the Optimize palette tab or choose Show Options from the Optimize palette menu.