## Basics on Enhancements

Because the human eye can't discern as many gray shades as can be displayed in most types satellite imagery, enhancements are needed. A typical satellite image on a monitor displays 256 gray shades. That is, a value from 0 to 255 is displayed for each pixel on a screen, 0 being black and 255 being white. The human eye can discern up to 64 shades of gray. Check down below to see for yourself.

16 gray shades

32 gray shades

64 gray shades

128 gray shades

It is difficult to discern between gray shades that are close together for typical digital imagery that has a brightness value range of 6 or more bits or more than 64 gray levels. Therefore, enhancements are used to exaggerate minor shading differences in features of interest. The process by which enhancements are created is simple, especially using image processing software. Raw brightness values are used as input and reassigned a different value as ouput. For example, a range of inputs maybe 100 to 150 which can be converted to 50 to 200. The contrast is larger in the output. For a closer look on how enhancements affect satellite imagery, consider the following:

#### Menu

- No enhancement
- Darkening or lightening imagery
- Stretching or shrinking contrasts
- The operational ZA enhancement curve
- The operational MB enhancement curve
- The operational BD enhancement curve
- Color enhancement curves

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