Method of compressing and decompressing graphic images

In a computer system, an apparatus for compressing graphics image data into a compressed block, the graphics image data comprising a plurality of pixels, each of the plurality of pixels having a color represented by red, green, blue, and intensity values, the apparatus comprising:

• (A) means for computing an epsilon value for the block, the epsilon value for the block being based on an attribute of the block;
• (B) means for mapping a color ordinal number to each pixel in the block by identifying a distinct color of the pixel based on the epsilon value and assigning to the pixel a corresponding color ordinal number, each color ordinal number representing one of the distinct colors present in the pixels of the block;
• (C) means for storing the red, green, blue, and intensity values of each distinct color present in the block into the compressed block;
• and
• (D) means for storing the color ordinal number mapped to each pixel in the block into the compressed block.

A computer-implemented method of compressing graphics image data into at least one compressed block comprising the steps of:

• (A) reading a block of graphics image data, the block having a plurality of pixels, each of the plurality of pixels having a color represented by red, green, blue, and intensity values;
• (B) computing an epsilon value for the block, the epsilon value for the block being based on a total brightness of the block;
• (C) mapping a color ordinal number to each pixel in the block by identifying a distinct color of the pixel based on the epsilon value and assigning to the pixel a corresponding color ordinal number, each color ordinal number representing one of the distinct colors present in the pixels of the block;
• (D) storing the red, green, blue, and intensity values of each distinct color present in the block into the compressed block;
• and
• (E) storing the color ordinal number mapped to each pixel in the block into the compressed block.

A computer-implemented method of compressing graphics image data into at least one compressed block comprising the steps of:

• (A) computing a work bit value representing a number of significant bits for each red, green, blue, and intensity values;
• (B) computing a quality level value representing a desired level of quality of graphics image data;
• (C) reading a block of graphics image data, the block having a plurality of pixels, each of the plurality of pixels having a color represented by red, green, blue, and intensity values;
• (D) computing a total brightness of the block, the total brightness of the block being based on an average of the red, green, and blue values of all the pixels in the block;
• (E) computing an epsilon value for the block, the epsilon value for the block being based on the total brightness of the block;
• (F) further adjusting the epsilon value based on the work bit value and quality level value;
• (G) mapping a color ordinal number to each pixel in the block by identifying a distinct color of the pixel based on the epsilon value and assigning to the pixel a corresponding color ordinal number, each color ordinal number representing one of the distinct colors present in the pixels of the block;
• (H) storing the red, green, blue, and intensity values of each distinct color present in the block based on the work bit value into the compressed block;
• (I) storing the color ordinal number mapped to each pixel in the block into the compressed block;
• (J) storing a number representative of the distinct colors present in the block, into the compressed block;
• and
• (K) repeating steps (C)-(J) for all blocks of graphics image data.