Error diffusion with color conversion and encoding
YCbCr image data may be dithered and converted into RGB data shown on a 8-bit or other bit display. Dither methods and image processors are provided which generate the banding artifact free image data during this process. Some methods and image processors may applying a stronger dither having a same mean with a larger variance to the image data before it is converted to RGB data. Others methods and image processors may calculate a quantization or encoding error and diffuse the calculated error among one or more neighboring pixel blocks.
1. A dithering method comprising:
encoding an original pixel block and generating a reconstructed pixel block therefrom;
comparing values of the original pixel block and the reconstructed pixel block;
applying an error function to a difference between the compared values to calculate an error statistic using a processing device; and
incorporating the error statistic in at least one value of at least one neighboring pixel block to the original pixel block.
2. The method of claim 1 , wherein the error statistic is incorporated in the at least one neighboring pixel block according to the following: block_j=block_j+w i,j ·g(E_i), where:
block j is a neighboring pixel block to the original pixel block i,
E_i is the error statistic for the original pixel block i,
w i,j is a diffusion coefficient specifying a distribution of the error statistic E_i to each neighboring pixel block j of the original pixel block i, and
g( ) is a compensation function generating a compensation signal returning the error statistic E_i when the error function is applied to the compensation function g(E_i).
3. The method of claim 2 , wherein E_i is an average error for the original pixel block i, the error function calculates a mean, and the compensation function generates a block with identical values.
4. The method of claim 2 , wherein E_i is a transform coefficient for the original pixel block i, the error function calculates a special transform efficient, and the compensation function generates an inverse transform.
5. The method of claim 2 , wherein E_i is an n-th moment for the original pixel block i, the error function calculates a moment, and the compensation function is an analytical generating function.
6. The method of claim 2 , wherein E_i is a vector of more than one error statistic.
7. The method of claim 2 , wherein w i,j is a fixed set of numbers.
8. The method of claim 2 , wherein w i,j varies depending on a size of at least one of the block i and the block j.
9. The method of claim 2 , wherein w i,j varies depending on a spatial connectivity between the block i and the block j.
10. The method of claim 2 , wherein w i,j varies depending on a difference between the block i and the block j.
11. The method of claim 10 , wherein w i,j is set to a lower value when a difference between a mean of the blocks i and j exceeds a threshold.
12. The method of claim 2 , further comprising:
identifying whether the blocks i and j are in a same banding area;
setting w i,j to a first value when the blocks i and j are in the same banding area; and
setting w i,j to a second value smaller than the first value when the blocks i and j are not in the same banding area.
13. The method of claim 2 , further comprising:
identifying an amount of texture in a neighborhood of at least one of the blocks i and j;
setting w i,j to a first value when the identified texture amount exceeds a threshold; and
setting w i,j to a second value higher than the first value when the identified texture amount does not exceed the threshold.
14. The method of claim 2 , further comprising:
identifying an amount of perceptual masking in a neighborhood of at least one of the blocks i and j;
setting w i,j to a first value when the identified masking amount exceeds a threshold; and
setting w i,j to a second value higher than the first value when the identified masking amount does not exceed the threshold.
15. The method of claim 1 , further comprising selecting a block size and a quantity of neighboring pixel blocks incorporating the error statistic based on whether a block is detected as part of a banding area.
16. The method of claim 1 , further comprising incorporating the error statistic in only those neighboring pixel blocks having transform units with transform sizes that are less than a threshold value.
17. The method of claim 1 , further comprising incorporating the error statistic in only those neighboring pixel blocks having transform units within a coding unit.
18. The method of claim 1 , further comprising incorporating the error statistic in only those neighboring pixel blocks having transform units within a prediction unit.
19. A dithering method comprising:
encoding an original pixel block and generating a reconstructed pixel block therefrom;
comparing values of the original pixel block and the reconstructed pixel block;
applying an error function to a difference between the compared values to calculate an error statistic using a processing device; and
incorporating the error statistic for a selected pixel in the original pixel block in at least one neighboring pixel value to the selected pixel in the original pixel block.
20. The method of claim 19 , further comprising iteratively repeating the method for a plurality of selected pixels and a plurality of original pixel blocks.
21. The method of claim 19 , further comprising incorporating a calculated error statistic transform coefficient for the selected pixel in a corresponding transform coefficient of the at least one neighboring pixel value in a transform domain.