Settings file created by Adobe Photoshop and Illustrator; contains settings for the "Save for Web" dialog; stores the image format (GIF, JPEG, PNG-8, PNG-24, or WBMP), quality, size, and other optimization options; enables Web designers to save multiple images that have the same formatting and quality specifications. You can open the Save for Web dialog in Photoshop CS5 by selecting File ? Save for Web & Devices.... Photoshop includes several preinstalled IRS files in the /Presets/Optimized Settings/ directory.