System and method for image mapping in linear space

• US 5,598,186 A
• Filed: 03/13/1995
• Issued: 01/28/1997
• Est. Priority Date: 07/30/1992
• Status: Expired due to Term

• Current Assignee: MediaTek, Inc.
• Original Assignee: International Business Machines Corporation
• Inventors: Edgar, Albert D.
• Primary Examiner(s): Weldon, Ulysses
• Assistant Examiner(s): LAO, LUNYI
• Application Number:
  US08/402,770
• Time in Patent Office: 687 Days
• Field of Search: 345/150, 345/153, 345/154, 345/186, 345/199, 348/674, 358/518, 358/519, 358/456, 358/447, 358/515, 358/517
• US Class Current: 345/603
• CPC Class Codes: G09G 5/06 using colour palettes, e.g. look-up tables
• CPC Class Codes: H04N 1/644 using a reduced set of representative colours, e.g. each representing a particular range in a colour space

Abstract

Red, green and blue pixels of a digitized image are combined to form a single vector that points to three lookup tables translating each pixel to linear Y, I, Q values thereby forming a linear image. The color value of each pixel in the linear image, comprised of Y, I, Q "aim" values, is then sequentially processed to attempt a match to the closest available colors. These three aim values point to respective lookup tables which translate them to three corresponding intermediate numbers which, when summed, point to a larger table mapping them to a number corresponding to the closest color in the predetermined palette. Three lookup tables translate the map number back to the linear space with corresponding mapped Y, I, Q values. The difference between these values and prior aim values constitutes error arising from the finite palette. The error is corrected with opposite error of adjoining pixels by error diffusion techniques.

Claims

1. A method for eliminating artifacts arising from display nonlinearities in an image of pixels forming image colors in a computerized digital image processing system having a predetermined finite multichromatic, full-tone palette of colors, comprising:

translating into the digital domain each of said pixels to a linear luminance aim value and two color aim values, said aim values being in a domain linearly proportional to lumens when said image is displayed;

selecting in nonlinear space three intermediate values from respective ones of three lookup tables formed from said translated pixels wherein the number of bits for each of said translated pixels remains the same when formed in said lookup tables, each of said intermediate values corresponding to a respective different one of said luminance aim value and two-color aim values;

wherein each of said lookup tables corresponds to respective three color vectors wherein said three color vectors are each comprised of a luminance vector corresponding to said luminance aim value and two color vectors corresponding to said two color aim values; and

forming, by summing said three intermediate values, a pointer from said three intermediate values;

defining a lookup table corresponding to a plurality of said pointers to colors of said predetermined palette;

selecting one of said colors from said predetermined palette in linear lumen space in functional relation to said pointer as a closest color in said predetermined palette to one of said image colors;

mapping said pointer to a color value in said lookup table corresponding to said closest palette color;

translating from said nonlinear space said mapped value back to linear space with corresponding mapped luminance and two color values;

repeating the preceding steps for each of said pixels to create a plurality of processed pixels; and

combining said processed pixels thereby effecting said eliminating of said artifacts and said display of said image.

2. The method of claim 1 further including the step of detecting differences between said aim values and said corresponding mapped luminance and two color values, wherein said differences comprise error arising from said finite palette.

3. The method of claim 2 further including repeating the preceding steps with respect to each of said pixels to determine an error associated with each of said pixels;

and

correcting said error by error diffusion of error of a given one of said pixels with error associated with pixels proximal said given one of said pixels.

4. The method of claim 2 wherein the step of detecting differences includes detecting differences for one of said pixels;

altering said linear luminance and two color aim values associated with an unmapped pixel; and

thereafter converting said unmapped pixel to aim values by translating with respect to said unmapped pixel linear luminance and two color aim values associated with said unmapped pixel.