# 4/221 Merge

4/221 Merge merges the 10.4 µm infrared channel (Channel 4 on AVHRR) with the regular 221 enhancement.

It provides increased contrast when compared to the regular 221 enhancement.

### Appearance

Land appears yellow (vegetated areas) or gray (deserts), while sea appears deep blue or black. 
Snow and ice appear white, including sea ice.
Clouds appear white.
Fog appears violet-white, but is hard to see.

### Intended usage

General purpose imagery at daytime.

### Limitations

Hard to determine the cloud nature.
Hard to discriminate between cirrus clouds and fog.