Image processing device and method for performing quality optimized deblocking

1. An image processing device deblocking a block edge between a first block and a second block of an image, the image processing device comprising:

at least one processor; and

one or more memories coupled to the at least one processor and storing programming instructions for execution by the at least one processor to cause the device to:

generate a filtered first pixel value from an original first pixel value of a first pixel, the first pixel being within a deblocking range from the block edge, the deblocking range comprising a number of pixels in a line perpendicular to the block edge, and the number of pixels comprises the first pixel and a second pixel;

determine a clipping value for the first pixel depending upon a distance of the first pixel from the block edge, using a lookup table;

clip the filtered first pixel value using the clipping value of the first pixel, resulting in a deblocked first pixel value;

generate a filtered second pixel value from an original second pixel value, the second pixel being within the deblocking range from the block edge; and

clip the filtered second pixel value using a constant clipping value, resulting in a deblocked second pixel value.

2. The image processing device of claim 1 , wherein the clipping value is a maximum allowed amount of change between the original first pixel value and the deblocked first pixel value.

3. The image processing device of claim 1 , wherein the clipping of the filtered first pixel value, using the clipping value, resulting in the deblocked first pixel value, comprises:

setting the deblocked first pixel value to the filtered first pixel value if the absolute value of a difference between the filtered first pixel value and the deblocked first pixel value does not exceed the clipping value of the first pixel,

setting the deblocked first pixel value to the original first pixel value plus the clipping value of the first pixel if the filtered first pixel value exceeds the original first pixel value plus the clipping value, and

setting the deblocked first pixel value to the original first pixel value minus the clipping value of the first pixel if the filtered first pixel value is lower than the original first pixel value minus the clipping value.

4. The image processing device of claim 1 , wherein the clipping value is a monotonically decreasing function of the distance of the first pixel from the block edge.

5. The image processing device of claim 4 , wherein the monotonically decreasing function is a linear function.

6. The image processing device of claim 5 , wherein the linear function is tc′=tc+(tc−(i*x), wherein tc′ is the clipping value, wherein tc is a constant value, wherein i is the distance of the first pixel from the block edge, and wherein x is a constant value.

7. The image processing device of claim 1 , wherein the at least one processor further executes the instructions to:

determine if the block edge needs to be filtered based upon a number of decision pixel lines being lower than a number of pixel lines in the blocks surrounding the block edge in the case of a vertical block edge, and upon a number of decision pixel rows being lower than a number of pixel rows in the blocks surrounding the block edge in the case of a horizontal block edge,

for each first pixel to be filtered that is not in a decision pixel row or decision pixel line and is within the deblocking range from the block edge, the deblocking range being perpendicular to the block edge:

determine the filtered first pixel value from the original first pixel value of the first pixel and the at least one further pixel value,

determine the clipping value of the first pixel depending upon the distance of the first pixel from the block edge,

clipping the filtered first pixel value using the clipping value, resulting in the deblocked first pixel value, and

for each second pixel to be filtered in the decision pixel row or the decision pixel line and is within the deblocking range from the block edge, the deblocking range being perpendicular to the block edge:

determine the filtered second pixel value from the original second pixel value of and the at least one additional pixel value, and

clipping the filtered second pixel value using the constant clipping value, resulting in the deblocked second pixel value.

8. The image processing device of claim 1 , wherein the at least one processor further executes the instructions to:

determine the filtered first pixel value from the original first pixel value of the first pixel and at least one further pixel value.

9. A deblocking method for deblocking a block edge between a first block and a second block of an image, the method comprising:

generating a filtered first pixel value from an original first pixel value of a first pixel, the first pixel being within a deblocking range from the block edge, the deblocking range comprising a number of pixels in a line perpendicular to the block edge, and the number of pixels comprises the first pixel and a second pixel;

determining a clipping value for the first pixel dependent upon a distance of the first pixel from the block edge using a lookup table;

clipping the filtered first pixel value using the clipping value of the first pixel, resulting in a deblocked first pixel value;

generating a filtered second pixel value from an original second pixel value, the second pixel being within the deblocking range from the block edge; and

clipping the filtered second pixel value using a constant clipping value, resulting in a deblocked second pixel value.

10. The method of claim 9 , wherein the clipping value is a maximum allowed amount of change between the original first pixel value and the deblocked first pixel value.

11. The method of claim 9 , wherein the clipping of the filtered first pixel value, using the clipping value, resulting in the deblocked first pixel value, comprises:

setting the deblocked first pixel value to the filtered first pixel value if the absolute value of a difference between the filtered first pixel value and the deblocked first pixel value does not exceed the clipping value of the first pixel,

setting the deblocked first pixel value to the original first pixel value plus the clipping value of the first pixel if the filtered first pixel value exceeds the original first pixel value plus the clipping value, and

setting the deblocked first pixel value to the original first pixel value minus the clipping value of the first pixel if the filtered first pixel value is lower than the original first pixel value minus the clipping value.

12. The method of claim 9 , wherein the clipping value is a monotonically decreasing function of the distance of the first pixel from the block edge.

13. The method of claim 12 , wherein the monotonically decreasing function is a linear function.

14. The method of claim 9 , wherein the filter is configured to determine the filtered first pixel value from the original first pixel value of the first pixel and at least one further pixel value.

15. A non-transitory computer-readable media storing computer instructions for performing a deblocking method for deblocking a block edge between a first block and a second block of an image, the instructions configure at least one processor, upon execution of the instructions, to perform the following steps:

generating a filtered first pixel value from an original first pixel value of a first pixel, the first pixel being within a deblocking range from the block edge, the deblocking range comprising a number of pixels in a line perpendicular to the block edge, and the number of pixels comprises the first pixel and a second pixel;

determining a clipping value for the first pixel depending upon a distance of the first pixel from the block edge, the determining using a lookup table;

clipping the filtered first pixel value using the clipping value of the first pixel, resulting in a deblocked first pixel value;

generating a filtered second pixel value from an original second pixel value, the second pixel being within the deblocking range from the block edge; and

clipping the filtered second pixel value using a constant clipping value, resulting in a deblocked second pixel value.

16. The image processing device of claim 1 , the image processing device being used in an image encoder and/or an image decoder.

17. The non-transitory computer-readable media of claim 15 , the computer-readable media being included in an image encoder and/or an image decoder.