Patent ID: 7586541

Claim:
A method comprising: reading a plurality of scan lines of a selected portion of a video signal into a signal matrix, the signal matrix having a plurality of rows that correspond to the plurality of scan lines, a row of the plurality of rows having a plurality of positions that correspond to the plurality of pixels; obtaining a plurality of difference values by subtracting each of the plurality of positions on the plurality of rows with a corresponding plurality of positions in a subsequent row of the selected portion; adding a difference value of the plurality of difference values to a line accumulator when the difference value is below a threshold value associated with the row; incrementing an in-range line count for the row when the line accumulator is within a range for the selected portion; and outputting a carrier absence for the selected portion when the in-range line count is less than or equal to an in-range threshold or a carrier presence for the selected portion when the in-range line count is greater than the in-range threshold.