Methods and Systems for Image Enhancement

• US 20110115815A1
• Filed: 11/18/2009
• Published: 05/19/2011
• Est. Priority Date: 11/18/2009
• Status: Abandoned Application

• Current Assignee: Sharp Laboratories of America Incorporated (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Laboratories of America Incorporated (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Xu, Xinyu, Kerofsky, Louis Joseph, Daly, Scott J.
• Application Number:
  US12/621,452
• Publication Number:
  US 20110115815A1
• Time in Patent Office: Days
• US Class Current: 345/626
• CPC Class Codes: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 2207/20028 Bilateral filtering
• CPC Class Codes: G06T 2207/20192 Edge enhancement; Edge preservation
• CPC Class Codes: G06T 5/73 Deblurring; Sharpening
• CPC Class Codes: G09G 2320/066 for control of contrast
• CPC Class Codes: G09G 5/003 Details of a display terminal, the details relating to the control arrangement of the display terminal and to the interfaces thereto specific for a CRT G09G1/165; for a flat panel G09G3/2092

Abstract

Aspects of the present invention are related to systems and methods for improving content visibility on a liquid crystal display (LCD) under low-contrast viewing conditions. According to one aspect of the present invention an enhanced image may be formed by combining a key-feature map associated with an input image and a brightness-boosted version of the input image.

Claims

1. A computer-implemented method for enhancing an input image, said method comprising:

a) receiving an input image in a computing device;

b) estimating a key-feature map associated with said input image;

c) forming a brightened image by boosting the brightness of said input image; and

d) combining said key-feature map and said brightened image to form an enhanced image.

2. The method as described in claim 1, wherein said forming is based on at least one of a backlight power level associated with an LCD display, an ambient light level and the image content of said input image.

3. The method as described in claim 1, wherein said forming comprises determining a brightening factor.

4. The method as described in claim 3, wherein said brightening factor is spatially varying.

5. The method as described in claim 1, wherein said forming comprises:

a) determining a first brightening factor;

b) receiving a first color component value associated with a first pixel in said input image;

c) receiving a second color component value associated with said first pixel;

d) receiving a third color component value associated with said first pixel;

e) modifying said first color component value, said second color component value and said third color component value by said first brightening factor when said first-brightening-factor modified first color component value is less than a maximum code value and said first-brightening-factor modified second color component value is less than said maximum code value and said first-brightening-factor modified third color component value is less than said maximum code value; and

f) when said first-brightening-factor modified first color component value is not less than said maximum code value or said first-brightening-factor modified second color component value is not less than said maximum code value or said first-brightening-factor modified third color component value is not less than said maximum code value;

i) determining a second brightening factor based on said maximum code value and the maximum of said first color component value, said second color component value and said third color component value;

ii) modifying said first color component value by said second brightening factor;

iii) modifying said second color component value by said second brightening factor; and

iv) modifying said third color component value by said second brightening factor.

6. The method as described in claim 1 further comprising mapping the pixel values of said enhanced image to code values associated with an LCD display.

7. The method as described in claim 1 further comprising:

a) selecting a blending-parameter value; and

b) using said blending-parameter value in said combining.

8. The method as described in claim 7, wherein said blending-parameter value is used to linearly weight said key-feature map and said brightened image.

9. The method as described in claim 1, wherein said estimating comprises calculating a gradient map from a gray-scale image formed from said input image, wherein said gradient-map calculation is a large-spatial-support calculation.

10. The method as described in claim 1, wherein said estimating comprises:

a) bilateral filtering a low-resolution image associated with said input image;

b) converting said bilateral filtered image to a gray-scale image;

c) performing a large-spatial-support gradient calculation on said gray-scale image, thereby producing a raw gradient map;

d) suppressing low-amplitude gradients in said raw gradient map;

e) reversing the polarity in said low-amplitude-gradient suppressed gradient map;

f) enhancing the gradient contrast in said reversed-polarity gradient map;

g) smoothing the gradient in said gradient-contrast enhanced gradient map; and

h) shifting the background of a gradient map formed from said smoothed gradient map to zero.

11. The method as described in claim 10, wherein said low-resolution image associated with said input image is formed by:

a) low-pass filtering said input image; and

b) down-sampling said low-pass-filtered input image.

12. The method as described in claim 11, wherein said gradient map formed from said smoothed gradient map is formed by up-scaling said smoothed gradient map to the resolution of said input image.

13. The method as described in claim 1, wherein said estimating comprises:

a) determining a first plurality of first-order derivative values in a first horizontal direction in relation to a first pixel location in a gray-scale image associated with said input image;

b) determining a second plurality of first-order derivative values in a second horizontal direction in relation to said first pixel location in said gray-scale image associated with said input image;

c) determining a third plurality of first-order derivative values in a first vertical direction in relation to said first pixel location in said gray-scale image associated with said input image;

d) determining a fourth plurality of first-order derivative values in a second vertical direction in relation to said first pixel location in said gray-scale image associated with said input image;

e) determining a first maximum value, wherein said first maximum value is the maximum value of said first plurality of first-order derivative values;

f) determining a second maximum value, wherein said second maximum value is the maximum value of said second plurality of first-order derivative values;

g) determining a third maximum value, wherein said third maximum value is the maximum value of said third plurality of first-order derivative values;

h) determining a fourth maximum value, wherein said fourth maximum value is the maximum value of said fourth plurality of first-order derivative values;

i) determining a horizontal-gradient value by adding said first maximum value and said second maximum value;

j) determining a vertical-gradient value by adding said third maximum value and said fourth maximum value; and

k) determining a gradient value associated with said pixel location, wherein said gradient value associated with said pixel location is the maximum of said horizontal-gradient value and said vertical-gradient value

14. A system for enhancing an input image, said system comprising:

a) a key-feature estimator for estimating a key-feature map associated with an input image;

b) a brightness booster for forming a brightened image by boosting the brightness of said input image; and

c) a combiner for combining said key-feature map and said brightened image to form an enhanced image.

15. The system as described in claim 14 further comprising a blending-parameter selector for selecting a blending parameter to be used by said combiner.

16. The system as described in claim 14 further comprising a code-value mapper for mapping the pixel values of said enhanced image to code values associated with an LCD display.

17. The system as described in claim 14, wherein said key-feature estimator comprises a gradient-map calculator for calculating a gradient map from a gray-scale image formed from said input image, wherein said gradient-map calculator uses a large-spatial-support in said gradient-map calculation.

18. The system as described in claim 14, wherein said key-feature estimator comprises:

a) a bilateral filter for filtering a low-resolution image associated with said input image;

b) a gray-scale converter for converting said bilateral filtered image to a gray-scale image;

c) a gradient calculator for performing a large-spatial-support gradient calculation on said gray-scale image, thereby producing a raw gradient map;

d) a low-amplitude gradient suppressor for suppressing low-amplitude gradients in said raw gradient map;

e) a gradient-map polarity reverser for reversing the polarity in said low-amplitude-gradient suppressed gradient map;

f) a gradient-contrast enhancer for enhancing the gradient contrast in said reversed-polarity gradient map;

g) a gradient smoother for smoothing the gradient in said gradient-contrast enhanced gradient map; and

h) a gradient-map shifter for shifting the background of a gradient map formed from said smoothed gradient map to zero.

19. The system as described in claim 14, wherein said key-feature calculator comprises:

a) a horizontal-gradient calculator for determining a horizontal gradient at a first pixel location in a gray-scale image associated with said input image, wherein said horizontal-gradient calculator;

i) determines a first plurality of first-order derivative values in a first horizontal direction in relation to said first pixel location;

ii) determines a second plurality of first-order derivative values in a second horizontal direction in relation to said first pixel location;

iii) determines a first maximum value, wherein said first maximum value is the maximum value of said first plurality of first-order derivative values;

iv) determines a second maximum value, wherein said second maximum value is the maximum value of said second plurality of first-order derivative values; and

v) determines a horizontal-gradient value by adding said first maximum value and said second maximum value;

b) a vertical-gradient calculator for determining a vertical gradient at a first pixel location in a gray-scale image associated with said input image, wherein said vertical-gradient calculator;

i) determines a third plurality of first-order derivative values in a first vertical direction in relation to said first pixel location;

ii) determines a fourth plurality of first-order derivative values in a second vertical direction in relation to said first pixel location;

iii) determines a third maximum value, wherein said third maximum value is the maximum value of said third plurality of first-order derivative values;

iv) determines a fourth maximum value, wherein said fourth maximum value is the maximum value of said fourth plurality of first-order derivative values; and

v) determines a vertical-gradient value by adding said third maximum value and said fourth maximum value; and

c) a pixel gradient determiner for determining a gradient value associated with said pixel location, wherein said gradient value associated with said pixel location is the maximum of said horizontal-gradient value and said vertical-gradient value.

20. The system as described in claim 14, wherein said brightness booster uses at least one of a backlight power level associated with an LCD display, an ambient light level and the image content of said input image in forming said brightened image.

21. An image-display system comprising:

a) an input-image receiver for receiving an input image;

b) a key-feature estimator for estimating a key-feature map associated with said input image;

c) a brightness booster for forming a brightened image by boosting the brightness of said input image;

d) a combiner for combining said gradient map and said brightened image to form an enhanced image; and

e) a display for displaying said enhanced image.