Indexed Color

Indexed Color mode will use a maximum of 256 colours. With this mode, file size is reduced with any change of appearance kept to a minimum. It is particularly useful for the Web and graphics. When a conversion is made, a colour table of the colours used is created. Either the original colour is used in the table or a nearest equivalent colour is simulated.

1. Open an image and go to
   Image > Mode > Indexed Color.

   Reducing a full colour image to a web safe palette can result in some losses. Choosing Adaptive under Palette can help.

2. For Options and Dither, a high Amount setting will also smooth any colour transitions. Click OK.
   These standard settings will generally give a very accurate transfer to a web-safe image.

3. However, the graphic image on the top right uses:
   

   Palette Colors Forced Dither

   Local (Selective) 12 Primaries None

4. The most interesting choice under Palette is Custom. Individual colours or groups of colours can be selected and changed. It's good for scientific use where certain areas are to be emphasized but equally useful for special effects.

1. Start with the fresh image again and go to Indexed Color.

2. For Palette, choose Custom.
   The Color Table pops up.

   Select a batch of the colour squares with the cursor and choose a new colour in the Color Picker. Click OK twice.

3. Select another batch of squares and choose another new colour. OK.

4. In the Color Table, under Table there are more options of:
   Black Body;
   Grayscale;
   Spectrum;
   System.

   The number of colour permutations is virtually infinite.

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