Apparatus and method for encoding an image generated in part by graphical commands
A method and apparatus for encoding an image is disclosed. A decomposition circuit comprises a set of pixel filters used to identify picture pixels, background pixels and text pixels of the image. An image encoding circuit comprises a lossy discrete transform encoder for encoding the picture pixels, a constant color lossless encoder for encoding the background pixels, and a discrete color lossless encoder for encoding the text pixels.
1. An apparatus for encoding an image, comprising:
a decomposition circuit comprising a set of pixel filters, the decomposition circuit enabled to use the set of pixel filters to identify, within the image, (i) a set of background pixels compliant with background requirements of a constant color and defined spatial relationships, (ii) a set of text pixels compliant with text requirements of contrasting the constant color and defined proximity to pixels of the set of background pixels, and (iii) a set of picture pixels incompliant with the background requirements and the text requirements; and
an image encoding circuit comprising:
a lossy discrete transform encoder enabled to encode the set of picture pixels;
a constant color lossless encoder enabled to encode a combination of the set of background pixels and the set of text pixels, as an encoding of a background image of the constant color; and
a discrete color lossless encoder enabled to encode the set of text pixels as an overlay over the background image.
2. The apparatus of claim 1 , wherein identifying the set of background pixels comprises:
identifying a contiguous set of pixels with the constant color that exceeds a threshold number of pixels; and
identifying additional pixels of the constant color, the additional pixels within a threshold distance from the contiguous set of pixels and separated from the contiguous set of pixels by a selection of the set of text pixels.
3. The apparatus of claim 1 , wherein identifying the set of text pixels comprises:
the set of pixel filters identifying a limited area of the set of text pixels as a result of the set of pixel filters detecting a threshold number of contrast detections for the limited area of the set of text pixels, each of the contrast detections exceeding a contrast threshold between adjacent pixels;
the set of pixel filters identifying the limited area of the set of text pixels as being adjacent to a selection of the set of background pixels; and
the set of pixel filters identifying a selection of the set of text pixels as pixels not included in the set of background pixels, the selection of the set of text pixels within a threshold distance of one pixel from the limited area of the set of text pixels.
4. The apparatus of claim 1 , wherein the set of pixel filters identifies pixels of the image not identified as text pixels or background pixels as the set of picture pixels.
5. The apparatus of claim 1 , wherein the lossy discrete transform encoder comprises one of a masked discrete wavelet transform encoder or a masked discrete cosine transform encoder.
6. The apparatus of claim 1 , wherein the constant color lossless encoder comprises one of a run length encoder or a predictive encoder.
7. The apparatus of claim 1 , wherein the discrete color lossless encoder comprises one of a masked color cache encoder or a masked dictionary encoder.
8. The apparatus of claim 1 , wherein the constant color lossless encoder is further enabled to identify at least a portion of the set of text pixels as don't care pixels, and to encode a selection of the don't care pixels as background.
9. The apparatus of claim 1 , wherein the image encoding circuit further comprises a pixel mask encoder enabled to encode positional information of the set of picture pixels, the set of background pixels, and the set of text pixels of the image.