Process for detecting black bars in a video image
View Patent ↗A process for detecting black bands in a video image within a luminance range corresponding to low luminance values comprises the steps of: calculating, for each line situated in a location in which a black band can be expected to be found if present in said video image, a value relating to a maximum number of occurrences of points having the same luminance value; averaging said value over said lines in said location; calculating a threshold dependent on said average; and, comparing said value relating to said maximum number of occurrences obtained for a new line with said threshold. Applications relate, for example, to the detection of the “letterbox” format.
1. A process for detecting black bands in a video image within a luminance range corresponding to low luminance values, comprising the steps of:
calculating, for each line situated in a location in which a black band can be expected to be found if present in said video image, a value relating to a maximum number of occurrences of points having the same luminance value;
averaging said value over said lines in said location;
calculating a threshold dependent on said average;
comparing said value relating to said maximum number of occurrences obtained for a new line with said threshold.
2. The process according to claim 1 , wherein the value relating to said maximum number of occurrences for a line is the maximum number of occurrences of the points of a complete line or of a line portion.
3. The process according to claim 2 , wherein the value relating to a maximum number of occurrences for each said line is a sum of the first, second and third greatest occurrences of the points of said complete line or of said line portion.
4. A process according to claim 3 , wherein the threshold relates to sum of said first, second and third greatest occurrences for a low signal-to-noise ratio.
5. A process according to claim 2 , wherein said threshold relates to said maximum number for a high signal-to-noise ratio.
6. A process according to claim 1 , wherein the threshold is also dependent on a signal-to-noise ratio of said video image.
7. A process according to claim 1 , wherein said threshold is a percentage of said average.
8. A process according to claim 7 , wherein said percentage is dependent on the value of said average, over said lines in said location, calculated for occurrences corresponding to the points of a complete line.
9. A process according to claim 1 , wherein said value relating to said maximum number of occurrences for each said line is calculated for all the points of said line.
10. A process according to claim 1 , comprising the further step of splitting said video image into vertical zones, and calculating said value relating to said number of occurrences for each said line only for those points of line portions corresponding to said zones.
11. A process according to claim 10 , comprising the further step of performing said comparison for various ones of said zones.
12. A process according to claim 11 , wherein said detection is dependent on a reliability criterion dependent on the number of identical detections for said various ones of said zones.
13. A process according to claim 1 , comprising the further step of performing said comparison over several of said video images.
14. A process according to claim 13 , wherein said detection is dependent on a reliability criterion dependent on said number of identical detections for said various ones of said video images.