You can specify the number of luma and chroma levels in a source clip with the Posterise command. Each frame in the clip is divided into an equal number of luma and chroma levels, and each pixel of the image is mapped to the closest matching level.

To modify the luma and chroma of a clip:

1. Select FX from the A/V Tools box and then click Posterise.

   The Posterise menu appears.

   
   

   (a) Posterise box  (b) Levels field  

2. Select the channel(s) from the Posterise box.

   Select:	To:
   Chroma	Reduce the number of chroma levels, or units, in a clip. Chroma levels affect the red, green, and blue channels individually. For example, setting the chroma level to 2 creates 2 levels of red, blue, and green.
   Luma	Reduce the number of luma levels, or units, in a clip.
   Luma & Chroma	Reduce the number of luma and chroma levels, or units, in a clip.

3. In the Levels field, specify the number of levels that will comprise the selected channel. Increasing the number decreases the posterising effect. Decreasing the number increases the effect.
4. Select the source clip.
5. Select the destination in the Source Area or the Record Area.

   The posterised clip appears in the selected destination.

   Original image

   Posterised image, Levels = 5