Method of generating transfer curves for adaptive contrast enhancement

• US 20060082689A1
• Filed: 01/26/2005
• Published: 04/20/2006
• Est. Priority Date: 10/15/2004
• Status: Active Grant

• Current Assignee: Genesis Microchip Inc. (STMicroelectronics NV)
• Original Assignee: Genesis Microchip Inc. (STMicroelectronics NV)
• Inventors: Moldvai, Caba
• Granted Patent: US 7,573,533 B2
• Time in Patent Office: Days
• US Class Current: 348/678
• CPC Class Codes: H04N 1/4052 by error diffusion, i.e. transferring the binarising error to neighbouring dot decisions
• CPC Class Codes: H04N 1/4074 using histograms

Abstract

Disclosed is a method for generating transfer curves for adaptive contrast enhancement. Transfer curves are generated so as to enhance the bright pixels in mostly dark images and the dark pixels in mostly bright images. For a dark image, a transfer curve is generated which increases luminance in high-luminance regions of the image without substantially changing the luminance in the mid- and low-luminance regions of the image. For a bright image, a transfer curve is generated which decreases the luminance in the dark areas of the image without substantially changing the luminance in the mid- and high-luminance regions of the image. For a medium-bright image, a transfer curve is generated with increases the luminance in the high-luminance range and decreases the luminance in the low-luminance range of the histogram without substantially changing the luminance in the medium-luminance range of the image.

Claims

1. A method for adaptive contrast enhancement of an image, comprising:

determining whether the image comprises mostly low-luminance pixels; and

increasing luminance levels for high-luminance pixels in the image when the image comprises mostly low-luminance pixels.

2. A method as recited in claim 1, further comprising generating a luminance histogram for the image to indicate whether the image comprises mostly low-luminance pixels.

3. A method as recited in claim 1, further comprising receiving the image via a digital or analog signal.

4. A method as recited in claim 1, further comprising displaying the image on a display.

5. A method as recited in claim 4, wherein the display is selected from the group consisting of an LCD screen, an OLED screen, a DLP screen, a CRT and a plasma panel.

6. A method for adaptive contrast enhancement of an image, comprising:

determining whether the image comprises mostly high-luminance pixels; and

decreasing luminance levels for low-luminance pixels in the image when the image comprises mostly high-luminance pixels.

7. A method as recited in claim 6, further comprising generating a luminance histogram for the image to indicate whether the image comprises mostly high-luminance pixels.

8. A method as recited in claim 6, further comprising receiving the image via a digital or analog signal.

9. A method as recited in claim 6, further comprising displaying the image on a display.

10. A method as recited in claim 9, wherein the display is selected from the group consisting of an LCD screen, an OLED screen, a DLP screen, a CRT and a plasma panel.

11. A method for adaptive contrast enhancement of an image, comprising:

determining whether the image comprises mostly medium-luminance pixels; and

decreasing luminance levels for low-luminance pixels and increasing luminance levels for high-luminance pixels in the image when the image comprises mostly medium-luminance pixels.

12. A method as recited in claim 11, further comprising generating a luminance histogram for the image to indicate whether the image comprises mostly medium-luminance pixels.

13. A method as recited in claim 11, further comprising receiving the image via a digital or analog signal.

14. A method as recited in claim 11, further comprising displaying the image on a display.

15. A method as recited in claim 14, wherein the display is selected from the group consisting of an LCD screen, an OLED screen, a DLP screen, a CRT and a plasma panel.

16. A method for controlling a display device, comprising:

receiving an image;

selecting a transfer curve according to a luminance histogram of the image; and

enhancing a contrast of the image according to the transfer curve;

wherein;

(a) the transfer curve increases luminance levels for high-luminance pixels without substantially changing luminance levels for mid- and low-luminance pixels in the image when the image comprises mostly low-luminance pixels;

(b) the transfer curve decreases luminance levels for low-luminance pixels without substantially changing luminance levels for mid- and high-luminance pixels in the image when the image comprises mostly high-luminance pixels; and

(c) the transfer curve increases luminance levels for high-luminance pixels and decreases luminance levels for low-luminance pixels in the image without substantially changing luminance levels for mid-luminance pixels when the image comprises mostly mid-luminance pixels.

17. A method as recited in claim 16, further comprising displaying the image on a display.

18. A method as recited in claim 17, wherein contrast enhancement is applied to a user-definable region in the display.

19. A method as recited in claim 16, further comprising generating the luminance histogram for the image.

20. An apparatus for adaptive contrast enhancement, comprising:

a controller for;

(a) receiving an image;

(b) selecting a transfer curve according to a luminance histogram of the image; and

(c) enhancing a contrast of the image according to the transfer curve, the transfer curve for

a. increasing luminance levels for high-luminance pixels without substantially changing luminance levels for medium- and low-luminance pixels in the image when the image comprises mostly low-luminance pixels;

b. decreasing luminance levels for low-luminance pixels without substantially changing luminance levels for medium- and high-luminance pixels in the image when the image comprises mostly high-luminance pixels; and

c. increasing luminance levels for high-luminance pixels and decreasing luminance levels for low-luminance pixels in the image without substantially changing luminance levels for medium-luminance pixels when the image comprises mostly medium-luminance pixels.

21. An apparatus as recited in claim 20, the controller further for:

(d) generating the luminance histogram of the image.

22. An apparatus as recited in claim 20, further comprising a display for displaying the image.

23. An apparatus as recited in claim 22, wherein the display is selected from the group consisting of an LCD screen, an OLED screen, a DLP screen, a CRT and a plasma panel.