Adaptive Thresholding - like Thresholding except choose values locally

Contrast Stretching - spreading out graylevel distribution

Histogram Equalization - general method of modifying intensity distribution

Logarithm Operator - reducing contrast of brighter regions

Exponential/`Raise to Power' Operator - enhancing contrast of brighter regions

Single-point processing is a simple method of image enhancement.
This technique determines a pixel value in the enhanced image dependent only on the value of the corresponding pixel in the input image.
The process can be described with the *mapping function*

where

The corresponding graph is shown in Figure 1.

Figure 1Graylevel transformation function for thresholding.

Point operators are also known as
*LUT-transformations*, because the
mapping function, in the case of a discrete image, can be implemented
in a look-up table (LUT).

A subgroup of the point processors is the set of anamorphosis operators. This notion describes all point operators with a strictly increasing or decreasing mapping function. Examples include the logarithm operator, exponential operator and contrast stretching, to name just a few.

An operator where *M* changes over the image is adaptive thresholding.
This is not a pure point operation anymore, because the mapping function, and therefore the output pixel value, depends on the local neighborhood of a pixel.