Radiometric Resolution

While the arrangement of pixels describes the spatial structure of an image, the radiometric characteristics

describe the actual information content in an image. Every time an image is acquired on film or by a

sensor, its sensitivity to the magnitude of the electromagnetic energy determines the radiometric

resolution. The radiometric resolution of an imaging system describes its ability to discriminate very

slight differences in energy The finer the radiometric resolution of a sensor, the more sensitive it is to

detecting small differences in reflected or emitted energy..

Imagery data are represented by positive digital numbers which vary from 0 to (one less than) a selected

power of 2. This range corresponds to the number of bits used for coding numbers in binary format. Each

bit records an exponent of power 2 (e.g. 1 bit=2 1=2). The maximum number of brightness levels

available depends on the number of bits used in representing the energy recorded. Thus, if a sensor used 8

bits to record the data, there would be 28=256 digital values available, ranging from 0 to 255. However, if

only 4 bits were used, then only 24=16 values ranging from 0 to 15 would be available. Thus, the

radiometric resolution would be much less. Image data are generally displayed in a range of grey tones,

with black representing a digital number of 0 and white representing the maximum value (for example,

255 in 8-bit data). By comparing a 2-bit image with an 8-bit image, we can see that there is a large

difference in the level of detail discernible depending on their radiometric resolutions..