Adobe 23101335 User Guide - Page 350

340 CHAPTER 12 Optimizing Images for the Web The results of matting GIF and PNG-8 images depend on the Transparency option. If you select Transparency, only the partially transparent pixels, such as those at the edge of an anti-aliased image, are matted. When the image is placed on a Web page, the Web background shows through the transparent pixels, and the edges of the image blend with the background. This feature prevents the halo effect that results when an anti-aliased image is placed on a background color that differs from the image's original background. This feature also prevents the jagged edges that result with GIF hard-edged transparency. If you deselect Transparency, fully transparent pixels are filled with the matte color, and partially transparent pixels are blended with the matte color. GIF with Transparency option selected, and with Transparency option deselected 4 Select a color from the Matte pop-up menu: • (Photoshop) Select Eyedropper (to use the color in the eyedropper sample box), White, Black, or Other (using the color picker). • (ImageReady) Select Foreground Color, Background Color, or Other (using the color picker), or select a color from the Matte pop-up palette. Creating hard-edged transparency in GIF and PNG-8 images When working with GIF or PNG-8 files, you can create hard-edged transparency, in which all pixels that are more than 50% transparent in the original image are fully transparent in the optimized image, and all pixels that are more than 50% opaque in the original image are fully opaque in the optimized image. Use hard-edged transparency when you don't know the background color of a Web page or when the Web page background is a pattern. However, keep in mind that hard-edged transparency can cause jagged edges in the image. To create a matted GIF or PNG image: 1 Open or create an image that contains transparency. 2 In the Optimize panel/palette, select GIF, PNG-8, or PNG-24 from the File Format menu. 3 For GIF and PNG-8 format, select of deselect the Transparency option as desired. GIF with hard-edged transparency, and displayed in browser (inset at 300% magnification)