Video signal gradation corrector which prevents excessive extension of the dynamic range

• US 5,294,986 A
• Filed: 05/22/1992
• Issued: 03/15/1994
• Est. Priority Date: 05/28/1991
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Kageyama, Atsuhisa, Tsuji, Toshiaki
• Primary Examiner(s): Kostak, Victor R.
• Application Number:
  US07/886,927
• Time in Patent Office: 662 Days
• Field of Search: 358/166, 358/160, 358/455, 358/37, 358/167, 358/163, 382/18
• US Class Current: 348/672
• CPC Class Codes: G06F 17/18 for evaluating statistical data , e.g. average values, frequency distributions, probability functions, regression analysis forecasting specially adapted for a specific administrative, business or logistic context G06Q10/04
• 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
• CPC Class Codes: H04N 5/20 Circuitry for controlling amplitude response

Abstract

A gradation corrector for use in a television receiver which can subject a signal at any luminance level to non-linear correction to provide optimum image quality. Memory stores therein luminance histogram of an input signal. On the basis of the data, a circuit detects a total frequency, a circuit detects luminance distribution, and a circuit detects the expanse of the luminance distribution. A circuit calculates a fixed value to be added. Further, a circuit detects a minimum luminance level, and a circuit detects an average luminance level. A circuit calculates an accumulation starting point and a circuit calculates an accumulation stopping point. An adder adds the calculated fixed value to the data in the memory. A circuit accumulates the results in the range from the accumulation starting point to the accumulation stopping point. The accumulation result is stored in memory. A circuit detects the maximum cumulative value, and a circuit normalizes all the data stored in the memory by use of this maximum value. The normalized data are stored in a memory. Thus, the input signal is subjected to optimum normalization by use of the normalized data.

Claims

1. A gradation corrector comprising:

a histogram memory device for storing the luminance histogram of a video luminance signal;

a limiter circuit, connected with said histogram memory, for limiting the data supplied from said histogram memory in accordance with a threshold level;

a total frequency detecting circuit for detecting the total frequency of the luminance histogram on the basis of the output signal from said histogram memory;

a luminance distribution detecting circuit for detecting the luminance distribution of said luminance histogram on the basis of the output signal from said total frequency detecting circuit and that from said histogram memory;

a dispersion coefficient calculating circuit for calculating the expanse of said luminance histogram on the basis of the output signal from said luminance distribution detecting circuit and that from said total frequency detecting circuit;

an adding value calculating circuit for calculating a fixed value to be added when a cumulative histogram is acquired on the basis of the calculation result supplied from said dispersion coefficient calculating circuit;

an adder for adding the calculation result from said adding value calculating circuit to the output signal from said histogram memory;

a minimum value detecting circuit for detecting the minimum luminance level of said luminance histogram on the basis of the output signal from said histogram memory;

an average luminance level detecting circuit for detecting the average luminance level of the video signal inputted to said histogram memory;

an accumulation starting luminance level calculating circuit for calculating the luminance level where accumulation should be started when the cumulative histogram is to be acquired, on the basis of the output signals from said average luminance level detecting circuit, said minimum value detecting circuit and said dispersion coefficient calculating circuit;

an accumulation stopping luminance level calculating circuit for calculating the luminance level where accumulation should be started when the cumulative histogram is to be acquired, on the basis of the output signal from said average luminance level detecting circuit;

a histogram accumulation circuit for accumulating the outputs from said adder while they are controlled by the output signals from said accumulation starting luminance level calculating circuit and said accumulation stopping luminance level calculating circuit;

a cumulative histogram memory device for storing the accumulation result;

a maximum cumulative value detecting circuit for detecting the maximum value of the cumulative histogram on the basis of the output signal from said cumulative histogram memory;

a look-up table operating circuit for normalizing the output signal from said cumulative histogram memory on the basis of the output signal from said maximum cumulative value detecting circuit;

a look-up table memory device for storing the operation result in said look-up table operating circuit to convert the inputted video luminance signal on the basis of the corresponding data and outputting the converted signal; and

a timing control circuit for controlling the operation of each of said circuits.

2. A gradation corrector according to claim 1, wherein said limiter circuit limits the data supplied from said histogram to an upper limit value.

3. A gradation corrector according to claim 1, wherein said limiter circuit limits a frequency of the data supplied from said histogram circuit.

4. A gradation corrector according to claim 3, wherein said limiter circuit limits said frequency of the data supplied from said histogram circuit to an upper value.