Dynamic gamma correction apparatus

• US 6,633,343 B2
• Filed: 03/12/2001
• Issued: 10/14/2003
• Est. Priority Date: 03/14/2000
• 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: Ito, Keiichi, Suzuki, Hidetoshi, Kageyama, Atsuhisa, Kunitani, Hisao, Ishikawa, Katsuya, Kakuya, Yuki, Okada, Nobutaka
• Primary Examiner(s): Miller, John
• Assistant Examiner(s): Natnael, Paulos M.
• Application Number:
  US09/803,660
• Publication Number:
  US 20020036716A1
• Time in Patent Office: 946 Days
• Field of Search: 348/674, 348/675, 348/671, 348/673, 348/254, 348/255, 348/677-79, 358/519, 358/455, 358/518, 345/600
• US Class Current: 348/674
• CPC Class Codes: H04N 5/202 Gamma control circuits for controlling camera response irrespective of the scene brightness H04N23/82

Abstract

An appropriate correction quantity is obtained for a video luminance signal on an individual video basis with a characteristic value, like the maximum or average value, of the luminance signal taken into account, thereby performing gray scale correction more effectively. A dynamic gamma correction apparatus for performing a correction on a video luminance signal includes: a correction start point control section for obtaining a correction start point, which is a lower limit of a given correction range, in accordance with a characteristic value of the luminance signal; a gamma correction quantity calculating section for obtaining a provisional correction quantity for the luminance signal to be corrected using the correction start point and the luminance signal; a gamma correction gain control section for obtaining a gain for the provisional correction quantity in accordance with the characteristic value of the luminance signal; a multiplier for obtaining a product of the provisional correction quantity and the gain as a gamma correction quantity; and an adder for obtaining a sum of the luminance signal and the gamma correction quantity and outputting the sum. The correction start point and the gain for the provisional correction quantity are controllable in accordance with the characteristic value of the luminance signal. Thus, an appropriate gamma correction quantity can be obtained as a final correction quantity.

Claims

1. A dynamic gamma correction apparatus for performing a correction on a video luminance signal, the apparatus comprising:

a correction start point control section for obtaining a correction start point, which is a lower limit of a given correction range, in accordance with a characteristic value of the luminance signal;

a gamma correction quantity calculating section for obtaining a provisional correction quantity for the luminance signal to be corrected using the correction start point and the luminance signal;

a gamma correction gain control section for obtaining a gain for the provisional correction quantity in accordance with the characteristic value of the luminance signal;

a multiplier for obtaining a product of the provisional correction quantity and the gain as a gamma correction quantity; and

an adder for obtaining a sum of the luminance signal and the gamma correction quantity and outputting the sum.

2. The dynamic gamma correction apparatus of claim 1, further comprising a maximum value detecting section for obtaining a maximum value of the luminance signal,

wherein the correction start point control section obtains the correction start point in accordance with the maximum value.

3. The dynamic gamma correction apparatus of claim 1, further comprising an average value detecting section for obtaining an average value of the luminance signal,

wherein the correction start point control section obtains the correction start point in accordance with the average value.

4. The dynamic gamma correction apparatus of claim 1, further comprising:

a maximum value detecting section for obtaining a maximum value of the luminance signal; and

an average value detecting section for obtaining an average value of the luminance signal,

wherein the correction start point control section obtains the correction start point in accordance with a difference obtained by subtracting the average value from the maximum value.

5. The dynamic gamma correction apparatus of claim 1, further comprising a minimum value detecting section for obtaining a minimum value of the luminance signal,

wherein the correction start point control section obtains the correction start point in accordance with the minimum value.

6. The dynamic gamma correction apparatus of claim 1, further comprising a maximum value detecting section for obtaining a maximum value of the luminance signal,

wherein the gamma correction gain control section obtains the gain in accordance with a value obtained by subtracting the maximum value from a preset maximum luminance.

7. The dynamic gamma correction apparatus of claim 1, further comprising an average value detecting section for obtaining an average value of the luminance signal,

wherein the gamma correction gain control section obtains the gain in accordance with a value obtained by subtracting a preset threshold value from the average value.

8. The dynamic gamma correction apparatus of claim 1, further comprising:

a maximum value detecting section for obtaining a maximum value of the luminance signal; and

an average value detecting section for obtaining an average value of the luminance signal,

wherein the gamma correction gain control section obtains the gain in accordance with the average and maximum values so that the higher the average value, the smaller the gain and that the lower the average value, the larger the gain.

9. The dynamic gamma correction apparatus of claim 1, wherein the gamma correction quantity calculating section obtains the provisional correction quantity by a linear function using the luminance signal to be corrected as a variable, and

wherein the linear function has a predetermined number of intervals where the greater a variable associated with one of the intervals, the greater a coefficient of the linear function associated with the interval.

10. The dynamic gamma correction apparatus of claim 9, further comprising a maximum value detecting section for obtaining a maximum value of the luminance signal,

wherein the gamma correction quantity calculating section determines the respective intervals of the linear function by the correction start point and the maximum value.