Digital image processing

DETAILED DESCRIPTION FIG.
1 is an illustration of a typical hardware layout according to an embodiment of the invention.
FIG.
2 shows a comparison between a 4-bit grey scale and an 8-bit grey scale.
FIG.
3 shows an 8-bit image of a motor vehicle including a licence plate area.
FIG.
4 is a graph of pixel intensity values for a typical speed violation image.
FIG.
5 is a diagram showing an algorithm for mapping 8-bit pixel intensity information to 4-bit information according to an embodiment of the invention.
FIGS.
6a and 6b are 4-bit versions of the image of FIG.
3, with mapping done according to the algorithm of FIG.
5.
FIG.
7 is a schematic diagram illustrating another pixel intensity compression algorithm.
FIG.
8 is a further schematic diagram illustrating the compression algorithm.
FIGS.
9a and 9b are 4-bit versions of the image of FIG.
3, with mapping done according to the algorithm of FIGS.
7 and 8.
FIGS.
10a and 10b are 4-bit versions of the image of FIG.
3, with mapping done according to the direct division algorithm.
FIG.
11 is a schematic representation of a digital camera suitable for use in conjunction with the method of the present invention.
FIG.
12 shows a representation of a 16-bit analog to digital converter suitable for use in the camera of FIG.
11.
FIG.
13 is a representation of a non-linear amplifier suitable for eliminating "optical burn" in accordance with the invention.
FIGS.
14a and 14b show an image of a vehicle with an over-exposed licence plate, a typical case of "optical burn".
FIG.
15 shows a portion of the images of FIGS.
14a and 14b after processing according to the invention so that the licence plate has become legible.
FIG.
1 shows a typical hardware layout for apparatus which uses the inventive method.
A light image is detected by a charge coupled device (CCD) 1, which is an element of a type which is used in video cameras.
The detected image is split into red, green and blue (RGB) analog streams, which are passed to analog to digital converters (A/D converters) 2