Low intensity contouring and color shift reduction using dither

• US 6,040,876 A
• Filed: 10/11/1996
• Issued: 03/21/2000
• Est. Priority Date: 10/13/1995
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Pettitt, Gregory S., Markandey, Vishal
• Primary Examiner(s): HSIA, SHERRIE Y
• Application Number:
  US08/729,121
• Time in Patent Office: 1,257 Days
• Field of Search: 345/136, 382/167, 382/275, 358/533, 358/519, 358/454, 358/463, 358/518, 358/457, 348/607, 348/27, 348/618, 348/574, 348/624, 348/627, 348/612, 348/615, 341/155, 341/131
• US Class Current: 348/624
• CPC Class Codes: G09G 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 3/2051 with use of a spatial dither pattern
• CPC Class Codes: G09G 5/02 characterised by the way in which colour is displayed details of colour display specific for CRTs G09G1/28; specific for flat matrix panels other than liquid crystal displays G09G3/2003; specific for liquid crystal displays G09G3/3607
• CPC Class Codes: H04N 21/426 Internal components of the client ; Characteristics thereof H04N5/44 takes precedence
• CPC Class Codes: H04N 9/643 Hue control means, e.g. flesh tone control
• CPC Class Codes: H04N 9/69 for modifying the colour signals by gamma correction controlling camera response for colour signals H04N23/83

Abstract

A method and system for reducing the effects of false contouring and reducing color shading artifacts. An image signal 102 is dithered by the addition of a small noise signal from a noise generator 500. The added noise signal breaks up the edges of homogenous blocks of pixels, causing the created image to appear to have a smooth transition from one region to the next. The image dithering is especially useful in digital color image displays where processing performed on the chrominance portion of the image signal often causes quantization errors which lead to sharp transitions between similar shades when the input image included a smooth transition.

Claims

1. A method of avoiding perceptual artifacts in an image display, said method comprising the steps of:

receiving a gamma corrected image signal, said gamma corrected image signal comprised of at least one luminance component and at least one chrominance component;

dithering one or more of said at least one chrominance component to form a dithered image signal, said dithering step operable to reduce image contouring in said dithered image signal;

converting said image signal to an RGB (red, green, blue) image signal;

removing said gamma correction from said RGB image signal; and

wherein said RGB image signal is comprised of three digital signal components, said method further comprising the step of reducing the number of data bits of said three signal components of said RGB image signal by dividing each of said digital signal components into a group of most significant bits and a group of least significant bits for each pixel of a pixelated image, wherein said most significant bits are transmitted to a spatial light modulator and said least significant bits are diffused to other pixels in said pixelated image.

2. The method of claim 1 wherein said dithering step comprises adding a random noise signal to one or more of said at least one chrominance components.

3. The method of claim 1, wherein said step of dithering comprises adding a noise signal to said at least one chrominance component of said image signal, wherein said noise signal has a digital value selected from the group of noise values consisting of +1, 0, and -1.

4. The method of claim 1, wherein said step of dithering comprises adding a noise signal to said at least one chrominance component of said image signal, wherein said noise signal has a digital value greater than 1 LSB.

5. A display system comprising:

digitizer for receiving a gamma corrected input image signal, said gamma corrected input image signal comprising at least one luminance component and at least one chrominance component;

at least one noise generator for generating a noise signal; and

an adder for adding said noise signal to said at least one chrominance component, wherein contouring in said input image signal is reduced;

a color space conversion circuit receiving said at least one luminance component and said at least one chrominance component with said noise signal added and outputting an RGB image signal having red, green, and blue components;

a degamma circuit for receiving said RGB image signal and removing said gamma correction from said RGB image signal;

an error diffusion filter receiving said RGB image signal and dividing each of said RGB signal components into a group of most significant bits and a group of least significant bits for each pixel of a pixelated image and diffusing said least significant bits to other pixels in said pixelated image;

a spatial light modulator receiving said most significant bits.

6. The display system of claim 5 wherein said noise generator is a random noise generator.

7. The display system of claim 5, wherein said noise generator is a pseudo-random noise generator.