Method and system for automatic brightness and contrast adjustment of a video source

• US 7,352,410 B2
• Filed: 05/31/2005
• Issued: 04/01/2008
• Est. Priority Date: 05/31/2005
• Status: Expired due to Fees

• Current Assignee: Corona Corporation
• Original Assignee: Kolorific Incorporated
• Inventors: Chou, Chih-Hsien
• Primary Examiner(s): Natnael; Paulos M.
• Application Number:
  US11/142,130
• Publication Number:
  US 20060268180A1
• Time in Patent Office: 1,036 Days
• Field of Search: 348/673, 348/672, 348/674, 348/675, 348/678, 348/679, 348/687, 382/168, 382/171
• US Class Current: 348/673
• CPC Class Codes: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/92 based on global image properties
• CPC Class Codes: G09G 2320/0238 Improving the black level
• CPC Class Codes: G09G 2320/0242 Compensation of deficiencies in the appearance of colours
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• 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 2320/0606 Manual adjustment
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: H04N 21/4318 by altering the content in the rendering process, e.g. blanking, blurring or masking an image region image enhancement or restoration in general G06T5/00
• CPC Class Codes: H04N 21/44008 involving operations for analysing video streams, e.g. detecting features or characteristics in the video stream arrangements characterised by components specially adapted for monitoring, identification or recognition of video in broadcast systems H04H60/59
• CPC Class Codes: H04N 5/58 in dependence upon ambient light

Abstract

An image brightness and contrast management module for automatically adjusting brightness and contrast of an input video signal includes a histogram generation unit that generates a pixel luminance histogram based on pixel luminance values in a frame, whereby the histogram shows a distribution of luminance values in the frame and indicates the dynamic range and the dominant luminance value(s) for the frame. The module includes a histogram characterization unit that uses the pixel luminance histogram to identify which of a plurality of brightness/contrast properties is exhibited in the frame. The module also includes a brightness and contrast adjustment unit that nonlinearly adjusts, in real-time, the pixel luminance values in a next frame based on the identified brightness/contrast properties exhibited in the preceding frame. In this manner, bright or dark dominant areas of an image are stretched to enhance the contrast of the dominant luminance values without blackening the darker portions or saturating the brighter portions of the image.

Claims

1. An image brightness and contrast management module for automatically adjusting brightness and contrast of an input video signal, the module comprising:

a histogram generation unit for generating, on a frame-by-frame basis, a pixel luminance histogram based on a luminance value of each of a plurality of pixels in a frame, wherein the histogram comprises a distribution of luminance values in the frame, the distribution indicating a dynamic range and at least one dominant luminance value for the frame;

a histogram characterization unit for analyzing the pixel luminance histogram for the frame and for identifying which of a plurality of brightness/contrast properties is exhibited in the frame; and

a brightness and contrast adjustment unit for nonlinearly adjusting in real-time the luminance values of the plurality of pixels in a next frame based on the identified brightness/contrast properties exhibited in a preceding frame,

such that bright or dark dominant areas of an image in the next frame are stretched to enhance the contrast of the dominant luminance values of the next frame without blackening the darker portions or saturating the brighter portions of the image.

2. The module of claim 1 wherein the histogram characterization unit includes at least one property analysis unit, wherein each property analysis unit is configured to analyze the pixel luminance histogram for the frame and to identify a particular brightness/contrast property based on the histogram.

3. The module of claim 2 wherein each property analysis unit calculates a property parameter indicating whether the frame exhibits the particular brightness/contrast property associated with the property analysis unit.

4. The module of claim 2 wherein the brightness and contrast adjustment unit includes a nonlinear adjustment unit associated with each property analysis unit, wherein the nonlinear adjustment unit is configured to correct the particular brightness/contrast property identified by the associated property analysis unit.

5. The module of claim 4 wherein each nonlinear adjustment unit calculates a luminance adjustment value, and the brightness and contrast adjustment unit sums each luminance adjustment value, adjusts the pixel luminance values of the pixels in the next frame according to the summed luminance adjustment values, and outputs the adjusted pixel luminance values to a display device.

6. The module of claim 5 wherein the histogram generation unit receives the outputted adjusted pixel luminance values for the next frame and generates a pixel luminance histogram based on the adjusted pixel luminance values of the next frame.

7. A video display system according to claim 1 wherein the brightness and contrast adjustment unit outputs the adjusted luminance values to a display device having a projector lamp or panel backlight coupled to a controller that controls the intensity of the projector lamp or panel backlight, and wherein the module further includes:

a lamp/backlight adjustment unit for controlling the intensity of the projector lamp or panel backlight based on either or both of the pixel luminance values of a frame and a measured ambient light level.

8. The module according to claim 1 further including a flicker reduction unit that comprises a temporal smoothing state machine with hysteresis within adjustment thresholds, wherein the flicker reduction unit suppresses unexpected changes in brightness to reduce image flickering.

9. A method for automatically adjusting brightness and contrast of an input video signal, the method comprising:

receiving pixel luminance values for each of a plurality of pixels in a frame;

generating, on a frame-by-frame basis, a pixel luminance histogram based on the pixel luminance values in the frame, wherein the histogram comprises a distribution of luminance values in the frame, the distribution indicating a dynamic range and at least one dominant luminance value for the frame;

identifying which of a plurality of brightness/contrast properties is exhibited in the frame based on the pixel luminance histogram;

receiving pixel luminance values for each of a plurality of pixels in a next frame; and

nonlinearly adjusting in real-time the pixel luminance values in the next frame based on the identified brightness/contrast properties exhibited in the preceding frame,

such that bright or dark dominant areas of an image in the next frame are stretched to enhance the contrast of the dominant luminance values of the next frame without blackening the darker portions or saturating the brighter portions of the image in the next frame.

10. The method according to claim 9 wherein identifying which of a plurality of brightness/contrast properties is exhibited in the frame includes:

for each brightness/contrast property, applying a weighting function to the pixel luminance histogram by performing a lookup in a weighting function lookup table associated with the brightness/contrast property, and applying a threshold function associated with the brightness/contrast property.

11. The method according to claim 10 wherein identifying which of a plurality of brightness/contrast properties is exhibited in the frame further includes:

for each brightness/contrast property, calculating a property parameter that indicates whether the frame exhibits the brightness/contrast property.

12. The method according to claim 9 wherein nonlinearly adjusting the pixel luminance values in the next frame includes:

for each identified brightness/contrast property exhibited in the frame, applying a nonlinear adjustment curve associated with the identified brightness/contrast property to the pixel luminance values for the next frame by performing a lookup in a nonlinear adjustment lookup table associated with the identified brightness/contrast property.

13. The method according to claim 12 wherein nonlinearly adjusting the pixel luminance values in the next frame further includes:

for each identified brightness/contrast property exhibited in the frame, calculating a luminance adjustment value,

summing the luminance adjustment values associated with each identified brightness/contrast property, and

adding the summed luminance adjustment values to the pixel luminance values in the next frame.

14. The method according to claim 9 further including:

outputting the adjusted pixel luminance values for the next frame to a display device such that the adjusted luminance values are displayed;

receiving the adjusted pixel luminance values to be displayed;

generating a pixel luminance histogram based on the adjusted pixel luminance values; and

repeating the automatic brightness and contrast adjustment process for another next frame.

15. The method according to claim 9 further including:

providing a display device that receives and displays the adjusted pixel luminance values using a projector lamp or panel backlight; and

controlling an intensity of the projector lamp or panel backlight based on either or both of the pixel luminance values of the frame and a measured ambient light level.

16. The method according to claim 9 further including:

utilizing a temporal smoothing state machine with hysteresis within adjustment thresholds to suppress unexpected changes in brightness, thereby reducing image flickering.

17. A progressive scan display system comprising:

a signal receiving unit;

a tuner box for transforming the signal into an analog signal;

a video decoder for transforming the analog signal into a plurality of interlaced video fields, wherein each video field comprises a plurality of pixels and each pixel is defined by a luminance value and chrominance data based on color differences;

a de-interlacing system for converting the interlaced video fields into a progressive video signal;

an image controller for adjusting the pixel data of the video signal, the image controller comprising;

an image brightness and contrast management module for automatically adjusting the luminance data of the video signal to suit a viewer'"'"'s tastes, the module comprising;

a histogram generation unit for generating, on a frame-by-frame basis, a pixel luminance histogram based on a luminance value of each of a plurality of pixels in a frame, wherein the histogram comprises a distribution of luminance values in the frame, the distribution indicating a dynamic range and at least one dominant luminance value for the frame;

a histogram characterization unit for analyzing the pixel luminance histogram for the frame and for identifying which of a plurality of brightness/contrast properties is exhibited in the frame; and

a brightness and contrast adjustment unit for nonlinearly adjusting in real-time the luminance values of the plurality of pixels in a next frame based on the identified brightness/contrast properties exhibited in a preceding frame; and

a display for displaying the adjusted progressive video signal.

18. The display system according to claim 17, wherein the image controller further includes a color management module for automatically adjusting chrominance data of an input pixel from the video signal.