Video signal processing device and method for processing gradation step
In a horizontal-direction processing section, a comparing circuit sequentially compares pixel values of two adjacent pixels in a video image. A detecting circuit detects a horizontal flat region in which a difference between the pixel values compared by the comparing circuit is within a specified range. A horizontal boundary of the detected region is determined by the following processing. If a difference or the level (inclination) of a change in pixel value between two pixels adjacent to each other across the boundary is within a specified range, the boundary is determined to be a step in a gradation region. Vertically oriented processing is done same as processing of a horizontal direction.
1. A video signal processing device comprising a horizontal-direction processor which processes a frame image in a quantized video signal in a horizontal direction and a vertical-direction processor which processes the frame image in a vertical direction,
the horizontal-direction processor comprising:
first comparator configured to compare sequentially pixel values of two pixels in the frame image which are adjacent to each other in the horizontal direction;
first region detector configured to detect a region in which a difference between the pixel values compared by the first comparator is within a specified range;
first determining unit configured to, if a difference or the level of a change in pixel value between two pixels adjacent to each other across a horizontal boundary of the region detected by the first region detector is within a specified range, determine the horizontal boundary to be a step in the gradation region or if the difference or the level of a change is out of the specified range, determine the horizontal boundary to be a boundary of another region; and
first gray level corrector configured to correct gray levels adjacent to each other across the horizontal boundary if the first determining unit determines the horizontal boundary to be a step in the gradation region,
the vertical-direction processor comprising:
second comparator to compare sequentially pixel values of two pixels in the frame image which are adjacent to each other in the vertical direction;
second region detector to detect a region in which a difference between the pixel values compared by the second comparing means is within a specified range;
second determining unit configured to, if a difference or the level of a change in pixel value between two pixels adjacent to each other across a vertical boundary of the region detected by the second region detector is within a specified range, determining the vertical boundary to be a step in the gradation region or if the difference or the level of a change is out of the specified range, determining the vertical boundary to be a boundary of another region; and
second gray level corrector configured to correct gray levels adjacent to each other across the vertical boundary if the second determining unit determines the vertical boundary to be a step in the gradation region.
2. The video signal processing device according to claim 1 , wherein each of the first and second gray level corrector executes a dither process on pixels adjacent to each other across the boundary.
3. The video signal processing device according to claim 2 , wherein the dither process is based on the difference in pixel value between the pixels adjacent to each other across the boundary or the level of a change in pixel value.
4. A method for processing a gradation step, the method being used for a video signal processing device which processes a frame image in a quantized video signal in horizontal and vertical directions,
the image processing in the horizontal direction comprising:
comparing sequentially first pixel values of two pixels in the frame image which are adjacent to each other in the horizontal direction;
detecting a first region in which a difference between the first pixel values compared in the comparing is within a specified range; and
determining, if a difference or the level of a change in pixel value between two pixels adjacent to each other across a horizontal boundary of the region detected in the first region is within a specified range, determining the horizontal boundary to be a step in the gradation region or if the difference or the level of a change is out of the specified range, determining the horizontal boundary to be a boundary of another region,
the image processing in the vertical direction comprising:
comparing sequentially second pixel values of two pixels in the frame image which are adjacent to each other in the horizontal direction;
detecting a second region in which a difference between the second pixel values compared in the comparing is within a specified range; and
determining, if a difference or the level of a change in pixel value between two pixels adjacent to each other across a horizontal boundary of the region detected in the second region is within a specified range, determining the horizontal boundary to be a step in the gradation region or if the difference or the level of a change is out of the specified range, determining the horizontal boundary to be a boundary of another region.
5. The method according to claim 1 , further comprising:
correcting first gray levels adjacent to each other across the horizontal boundary if the determining determines the horizontal boundary to be a step in the gradation region; and
correcting second gray levels adjacent to each other across the vertical boundary if the determining determines the vertical boundary to be a step in the gradation region;
wherein each of the correcting the first and second gray level executes a dither process on pixels adjacent to each other across the boundary.
6. The method according to claim 5 , wherein the dither process is based on the difference in pixel value between the pixels adjacent to each other across the boundary or the level of a change in pixel value.