Gradation correction method and device

• US 6,101,271 A
• Filed: 03/21/1997
• Issued: 08/08/2000
• Est. Priority Date: 10/09/1990
• Status: Expired due to Fees

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Ishihara, Hideshi, Matsumoto, Yasuki, Yamashita, Haruo
• Primary Examiner(s): NGUYEN, ANH-VINH THI
• Application Number:
  US08/821,794
• Time in Patent Office: 1,236 Days
• Field of Search: 382/167, 382/162, 382/164, 382/165, 358/518-521, 358/519, 358/520, 358/523, 358/1.9
• US Class Current: 382/167
• CPC Class Codes: H04N 9/69 for modifying the colour signals by gamma correction controlling camera response for colour signals H04N23/83

Abstract

The gradation correction device includes a luminance signal convertor to generate a luminance signal from the input R, G, B signals, a correction coefficient calculator which calculates the ratio to the luminance signal of the luminance signal after gamma correction to the predetermined gradation characteristics, and a multipliers to multiply the output from the correction coefficient calculator by each of the R, G, and B input signals. When the gradation correction is applied, effective brightness adjustment can be applied with no change in hue and saturation and without exceeding the dynamic range of a device.

Claims

1. A gradation correction method for processing an image having red, green and blue signals, the method comprising the steps of:

converting said red, green and blue signals into a luminance signal;

using a digital table for receiving a digital address Y which represents the luminance signal and producing a digital output K which represents a correction coefficient defined as K=Y'"'"'/Y, wherein Y'"'"' represents a gamma converted luminance signal; and

multiplying said correction coefficient with each of said red, green and blue output signals, respectively, whereby outputs of first, second and third multipliers are converted red signal, converted green signal, and converted blue signal, respectively.

2. A gradation correction device for processing an image having red, green and blue signals, comprising:

a converter for converting said red, green and blue signals into a luminance signal;

a digital table for receiving a digital address Y which represents the luminance signal and producing a digital output K which represents a correction coefficient defined as K=Y'"'"'/Y, wherein Y'"'"' represents a gamma converted luminance signal; and

first, second and third multipliers for multiplying said correction coefficient with each of said red, green and blue signals, respectively, whereby outputs of said first, second and third multipliers are converted red signal, converted green signal and converted blue signal, respectively.

3. A gradation correction device for correcting red, green and blue signals comprising:

means for providing red, green and blue signals which correspond to a video image;

a luminance signal conversion means for generating a luminance signal from said red, green and blue signals;

a gamma conversion means for gamma converting the luminance signal to predetermined gradation characteristics and for producing a gamma converted luminance signal;

a multiplier means for multiplying the gamma converted luminance signal with each of said red, green and blue signals; and

a divider means for dividing the outputs of said multiplier means by the output of the luminance signal.

4. A gradation correction device for correcting red, green and blue signals comprising:

means for providing red, green and blue signals which correspond to a video image;

a luminance signal conversion means for generating a luminance signal from said red, green and blue signals;

a correction coefficient calculation means for calculating a ratio of a difference between a gamma converted luminance signal and non-converted luminance signal to the non-converted luminance signal;

a multiplier means for multiplying said ratio with each of said red, green and blue signals; and

an adder means for adding each of the outputs of said multiplier means to corresponding one of said red, green and blue signals.