Automatic contrast correction device and automatic contrast correction method

• US 20080008382A1
• Filed: 06/29/2007
• Published: 01/10/2008
• Est. Priority Date: 07/03/2006
• Status: Abandoned Application

• Current Assignee: Seiko Instruments Incorporated (Seiko Group)
• Original Assignee: Seiko Instruments Incorporated (Seiko Group)
• Inventors: Matsushima, Kenichi
• Application Number:
  US11/824,296
• Publication Number:
  US 20080008382A1
• Time in Patent Office: Days
• US Class Current: 382/167
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/92 based on global image properties
• CPC Class Codes: H04N 1/4074 using histograms

Abstract

Provided are an automatic contrast correction device and an automatic contrast correction method for a pictorial image constituted by luminance values for two-dimensionally arranged pixels capable of performing automatic correction to obtain a suitable contrast to human eyes corresponding to perception in a human brain. In order to obtain an optimized gradation characteristic for conversion, a frequency distribution is nonlinearly converted corresponding to a nonlinear perception of stimulus in a human brain to become flat. The conversion can generally keep an original characteristic of a picture having a good appearance to human eyes.

Claims

1. An automatic contrast correction device for receiving an input image including two-dimensionally arranged luminance information, and automatically correcting a contrast of the input image to generate a corrected output image, comprising:

a frequency distribution counter for obtaining a frequency distribution of the input image for each luminance value thereof;

a nonlinear converter for receiving a frequency distribution from the frequency distribution counter, and converting a frequency for each luminance based on one of a nonlinear function and a nonlinear table to generate a nonlinear frequency distribution;

an accumulation converter for accumulating the nonlinear frequency distribution from the nonlinear converter to generate a gradation conversion characteristic;

a gradation converter for converting the input image based on the gradation conversion characteristic from the accumulation converter; and

a controller for controlling entire status and timing.

2. An automatic contrast correction device according to claim 1, wherein one of the nonlinear function and the nonlinear table for the nonlinear converter comprises one of a function and a table corresponding to a characteristic of a stimulus in a human brain.

3. An automatic contrast correction device according to claim 1, wherein one of the nonlinear function and the nonlinear table for the nonlinear converter comprises one of a logarithmic function and a table produced based on the logarithmic function.

4. An automatic contrast correction device according to claim 1, wherein the one of the nonlinear function and the nonlinear table comprises one of a power function and a table produced based on the power function.

5. An automatic contrast correction device according to claim 4, wherein the nonlinear converter comprises a power function whose exponent is equal to or larger than one fourth and equal to or smaller than one half.

6. An automatic contrast correction device according to claim 1, wherein the gradation conversion characteristic converts the input image to have luminance information such that each pixel has a luminance value not smaller than that of the input image.

7. An automatic contrast correction device according to claim 1, wherein the input image has a linear characteristic.

8. An automatic contrast correction method for receiving an input image including two-dimensionally arranged luminance information, and automatically correcting a contrast of the input image to generate an corrected output image, comprising:

generating a frequency distribution of the input image for each luminance value by counting a number of pixels having a same luminance value;

converting each frequency of the frequency distribution for each luminance based on one of a nonlinear function and a nonlinear table to generate a nonlinear frequency distribution;

accumulating the nonlinear frequency distribution to generate a gradation conversion characteristic; and

converting the input image according to the gradation conversion characteristic.

9. An automatic contrast correction method according to claim 8, wherein the one of a nonlinear function and a nonlinear table comprises one of a function and a table corresponding to a characteristic of a stimulus applied to a person'"'"'s brain.

10. An automatic contrast correction method according to claim 8, wherein the one of a nonlinear function and a nonlinear table comprises one of a logarithmic function and a table produced based on the logarithmic function.

11. An automatic contrast correction method according to claim 8, wherein the one of a nonlinear function and a nonlinear table comprises one of a power function and a table produced based on the power function as one of the nonlinear function and the nonlinear table.

12. An automatic contrast correction method according to claim 11, wherein the power function has an exponent in a range of equal to or larger than ¼

and equal to or smaller than ½

.

13. An automatic contrast correction method according to claim 8, wherein the gradation conversion characteristic converts the input image to have luminance information such that each pixel has a luminance value not smaller than that of the input image.

14. An automatic contrast correction method according to claim 8, wherein the input image has a linear characteristic.