Method of generating transfer curves for adaptive contrast enhancement

• US 7,573,533 B2
• Filed: 01/26/2005
• Issued: 08/11/2009
• 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
• Primary Examiner(s): Tran; Trang U
• Application Number:
  US11/044,774
• Publication Number:
  US 20060082689A1
• Time in Patent Office: 1,658 Days
• Field of Search: 348/678, 348/34, 348/353, 348/365, 348/404.1, 348/424.2, 348/603, 348/673, 348/686, 345/589, 345/601, 345/606, 345/617, 382168-172, 382/274
• 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 enhancing contrast of an image displayed on a display device comprising:

receiving the image;

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

enhancing the contrast of the image to produce an output image according to the transfer curve by,

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

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

(c) increasing 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 only when the image comprises mostly mid-luminance pixels; and

displaying the output image on the display device.

2. A method as recited in claim 1, wherein the display device is selected from the group consisting of an LCD screen, an OLED screen, a DLP screen, a CRT and a plasma panel.

3. A method as recited in claim 1, wherein contrast enhancement is applied to a user-definable region in the display.

4. A method as recited in claim 1, further comprising generating the luminance histogram for the image.

5. A method as recited in claim 1, wherein the luminance ranges for low-, medium-, and high-luminance pixels are user-defined.

6. A method as recited in claim 1, wherein the luminance ranges for low-, medium-, and high-luminance pixels overlap in order to provide smooth contrast enhancement.

7. An apparatus for adaptive contrast enhancement, comprising:

a display for displaying an output image; and

a controller for;

(a) receiving an image;

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

(c) enhancing a contrast of the image according to the transfer curve to produce the output image, 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 only 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 only 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 only when the image comprises mostly medium-luminance pixels;

(d) providing the output image to the display for displaying.

8. An apparatus as recited in claim 7, the controller further for:

(e) generating the luminance histogram of the image.

9. An apparatus as recited in claim 7, 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.

10. An apparatus as recited in claim 7, wherein the luminance ranges for low-, medium-, and high-luminance pixels are user-defined.

11. An apparatus as recited in claim 7, wherein the luminance ranges for low-, medium-, and high-luminance pixels overlap in order to provide smooth contrast enhancement.