Image DN values
Each image element (pixel) is described by a meaningful digital number (DN)
DN reflects radiation value, reflected by the earth syrface, measured by a sensor. As the resulted data files are binary, the image DN values cannot be seen using a normal ASCII file editor.
The DN value for a single pixel can be written using 8 to 24 bits depending on range of DN values obtained from the sensor
During image processing, the DN values are used. When a visual interpretation is done, these DN values are "translated" into grey values (different levels of brightness of white).