Dithering in Photoshop

Dithering in Photoshop:

What is Dithering?

The process of dithering places pixels of two different colors next to each other to suggest the appearance of a third color. For example, in a grayscale photograph, a black pixel is placed next to a white pixel to suggest a shade of gray when viewed from a distance. This same process is used with color pixels to increase the number of colors that can be represented by a limited palette.

Unless you’re using the Exact color table option, the color table may not contain all the colors used I the image. To simulate colors not in the color table, you can dither the colors. Dithering mixes the pixels of the available colors to simulate the missing colors.

Choose a dither option from the menu, and enter a value for the dither amount. A higher amount dithers more colors, but may increase file size. You can choose from the following dither options:

None:

Does not dither colors but instead uses the color closest to the missing color. This tends to result in sharp transitions between shades of color in the image, creating a posterized effect.

Diffusion:

Uses an error – diffusion method that produces a less structured dither than the Pattern option. To protect colors in the image that contain entries in the color table from being dithered, select Preserve Exact Colors. This is useful for preserving fine lines and text for Web images.

Patterns:

Uses a halftone – like square pattern to simulate any colors not in the color table.

Noise:

Helps to reduce seam patterns along the edges of image slices. Choose this option if you plan to slice the image for placement in an HTML table.