Adobe 23101335 User Guide - Page 352
Previewing and controlling application, dither, Photoshop or ImageReady, and the Color Table
![]() |
UPC - 718659152833
View all Adobe 23101335 manuals
Add to My Manuals
Save this manual to your list of manuals |
Page 352 highlights
342 CHAPTER 12 Optimizing Images for the Web When optimizing images, keep in mind that two kinds of dithering can occur: • Application dither occurs in GIF and PNG-8 images when Photoshop or ImageReady attempts to simulate colors that appear in the original image but not in the color palette you specify for the optimized image. You can control the application dither that Photoshop or ImageReady applies to an optimized image. You can choose a dithering pattern to be applied to the image. In addition, you can create customized dither patterns for GIF or PNG-8 images using the DitherBox filter. (See "Creating and applying custom dither patterns" on page 344.) Note: Applying a dithering pattern is not recommended for JPEG or PNG-24 images. • Browser dither occurs when a Web browser using an 8-bit color display (256-color mode) attempts to simulate colors that appear in an optimized image but not in the color palette used by the browser. Browser dither can occur with GIF, PNG, or JPEG images and can occur in addition to application dither in GIF or PNG-8 images. You can control the amount of browser dither by shifting selected colors in the image to Web-safe colors. Options in the color picker, the Color palette in Photoshop or ImageReady, and the Color Table panel (Photoshop) or the Color Table palette (ImageReady) let you specify Web-safe colors when choosing a color. Previewing and controlling application dither You can preview application dither in GIF and PNG-8 images. The Dither Algorithm pop-up menu lets you choose a dithering method for the image. Images with primarily solid colors may work well with Dither set to none. Images with continuous-tone color (especially color gradients) may require dithering to prevent color banding. To control application dither: 1 Choose an option from the Dither Algorithm pop-up menu: • No Dither applies no application dither to the image. • Pattern applies a halftone-like square pattern to simulate any colors not in the color table. • Diffusion applies a random pattern that is usually less noticeable than Pattern dither. The dither effects are diffused across adjacent pixels. Diffusion dither may cause detectable seams to appear across slice boundaries. Linking slices diffuses the dither pattern across all linked slices, and eliminates the seams. • Noise applies a random pattern similar to the Diffusion dither method, but without diffusing the pattern across adjacent pixels. No seams appear with the Noise dither method. 2 If you chose Diffusion as the dithering algorithm, drag the Dither slider or enter a value to select a dithering percentage.
![](/manual_guide/products/adobe-23101335-user-guide-fbfeba3/352.png)