Encoding system for error diffusion dithering
An error diffusion system in accordance with an embodiment of the present invention adjusts the color depth of an RGB signal using error diffusion without the using an expensive frame buffer. Specifically, a color depth adjustment unit in accordance with the present invention can perform error diffusion on an RGB signal using two error buffers, which are smaller in memory size than typical line buffers that would be used for the video stream.
1. A color depth adjustment unit for converting an input video signal into an output video signal, wherein the input video signal has a plurality of input pixels having a plurality of input color portions of an input color size, and wherein the output video signal has a plurality of output pixels having a plurality of output color portions of an output color size; the color depth adjustment unit comprising:
an error diffusion unit coupled to receive the input video signal and to generate the output video signal;
a first error buffer coupled to the error diffusion unit and having a plurality of error memory units having a plurality of color portions of an error buffer size;
a second error buffer coupled to the error diffusion unit; and
wherein the error buffer size is less than the input color size.
2. The color depth adjustment unit of claim 1 , further comprising a next pixel error register coupled to the error diffusion unit.
3. The color depth adjustment unit of claim 2 , further comprising an error shift register coupled to the error diffusion unit, the first error buffer, and the second error buffer.
4. The color depth adjustment unit of claim 3 , wherein the error shift register comprises:
a first error shift stage coupled to the error diffusion unit, the first error buffer and the second error buffer;
a second error shift stage coupled to the first error shift stage and the error diffusion unit; and
a third error shift stage coupled to the second error shift stage and the error diffusion unit.
5. The color depth adjustment unit of claim 4 , wherein the error diffusion unit is configured to add an error value from the first error buffer to a color value of an input pixel and to determine a first input value and a first input error for the input pixel.
6. The color depth adjustment unit of claim 5 , wherein the color value corresponds to a red value.
7. The color depth adjustment unit of claim 5 , wherein the color value corresponds to a green value.
8. The color depth adjustment unit of claim 5 , wherein the color value corresponds to a blue value.
9. The color depth adjustment unit of claim 5 , wherein the error diffusion unit is configured to calculate a first output value and a first output error for the input pixel.
10. The color depth adjustment unit of claim 5 , wherein the error diffusion unit is configured to distribute the first output error.
11. The color depth adjustment unit of claim 10 , wherein the a first portion of the first output error is distributed to the next pixel error register, a second portion of the first output error is distributed to the third error shift stage, a third portion of the first error is added to the second error shift stage, and a fourth portion of the first error is added to the first error shift stage.
12. The color depth adjustment unit of claim 11 , wherein a content value of the first error shift stage is written to a error memory unit of the second error buffer.
13. The color depth adjustment unit of claim 1 , wherein the error diffusion unit is configured to add an error value from the first error buffer to a color value of an input pixel and to determine a first input value and a first input error for the input pixel.
14. The color depth adjustment unit of claim 13 , wherein the error diffusion unit is configured to calculate a first output value and a first output error for the input pixel.
15. The color depth adjustment unit of claim 14 , wherein the error diffusion unit is configured to distribute the first output error.