Technical Terminology

• Dither refers to an image on a computer display or in print that does not have sharp edges in order to appear to show more colors than are readily available. The use of dithering was more common when computer screens had limited means to show the full range of colors in a color image. Dithering can reduce the range of a colors in an image to 256 or fewer as viewed in 8-bit GIF images.
  
  

Creating an Illusion

• Dithering in essence mixes pixels of two colors to create an illusion of a third. This provides a smoother transition of colors and blending of shades than you would otherwise see. The downside is that dithering reduces the sharpness of the image.
  
  

Use in InDesign

• InDesign allows the user to place a Photoshop image in a page layout using Photoshop's advanced color conversion options. The user can select dither and convert 8-bit-per-channel images to simulate colors missing in the image's final color space, such as on a Web browser with limited resolution. Dithering blends color transitions to reduce a banded appearance in the image, but it can also increase the size of the file.
  
  

Expert Use

• InDesign strongly recommends that unless you are an expert in color management, you should leave the color conversion options alone. As most screens are now capable of showing millions of colors designers often simply ignore the browser-safe color palette and instead use GIF images with custom colors or display full color JPEG images.