Unit for and method of video signal enhancement and image display apparatus provided with such a video signal enhancement unit

1. A video signal enhancement unit comprising:

a pixel counter for generating a count of pixels representative of the number of pixels that have video signal levels higher than a predetermined video level;

a processing unit for modifying contrast of the video signal in dependence on the count of pixels;

a contrast counter for providing control input for the processing unit, said contrast counter storing a contrast count that is decreased each time the count of pixels exceeds a predefined threshold; and

a trigger means, coupled to the contrast counter, for generating a pulse resulting in an increase of the contrast count.

2. The video signal enhancement unit as claimed in claim 1 , characterized in that the trigger means generates the pulse every video field.

3. The video signal enhancement unit as claimed in claim 1 , characterized in that said video signal enhancement unit further comprises a second pixel counter, substantially similar to said pixel counter, for generating a second count of pixels representative of a second number of pixels that have video signal levels higher than a second predetermined video level, the trigger means generating the pulse if the second count of pixels is less than a second predefined threshold.

4. The video signal enhancement unit as claimed in claim 1 , characterized in that said video signal enhancement unit further comprises a contrast comparator coupled to the contrast counter, said contrast comparator limiting the contrast count to a maximum contrast value.

5. The video signal enhancement unit as claimed in claim 4 , characterized in that the maximum contrast value is controllable.

6. The video signal enhancement unit as claimed in claim 4 , characterized in that the contrast comparator controls the trigger means to stop generating pulses when the contrast count has reached the maximum contrast value.

7. An image display apparatus comprising:

receiving means for receiving a video signal;

a display device for displaying images represented by the video signal; and

a video signal enhancement unit comprising:

a pixel counter for generating a count of pixels representative of the number of pixels that have video signal levels higher than a predetermined video level;

a processing unit for modifying contrast of the video signal in dependence on the pixel count;

a contrast counter for providing a control input for the processing unit and for storing a contrast count that is decreased each time the count of pixels exceeds a predefined threshold; and

a trigger means, coupled to the contrast counter, for generating a pulse resulting in an increase of the contrast count.

8. The image display apparatus as claimed in claim 7 , characterized in that the trigger means generates a pulse every video field.

9. The image display apparatus as claimed in claim 7 , characterized in that the video signal enhancement unit further comprises a contrast comparator coupled to the contrast counter, said contrast comparator limiting the contrast count to a maximum contrast value.

10. A method of video signal enhancement comprising the steps:

generating a count of pixels representative of the number of pixels in the video signal that have video signal levels higher than a predetermined video level;

modifying contrast of the video signal in dependence on contrast count;

storing the contrast count, and decreasing the stored contrast count each time the count of pixels exceeds a predefined threshold; and

increasing the contrast count in response to a trigger pulse.