Effects > Distort > Pixelate
Pixelate
The Pixelate filter allows you to clump pixels into square blocks. The pixels in a given block are the same color, and the colors of the blocks represent the colors in the selection.
1. Do one of the following:
 Choose Effects > Distort > Pixelate
 
Click the Pixelate button
2. Use the following options:
  Pixel Size (px)
This option allows you to change the square size.

Min = 1, Max = 200, Default = 8.
  Grid
This option allows you to draw grid lines.
  Dots
This option allows you to use a grid made of dots, instead of squares.
  Background Color
This option allows you to change the background color.
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