Method for processing video signal and apparatus for processing video signal

• US 6,356,304 B1
• Filed: 04/22/1997
• Issued: 03/12/2002
• Est. Priority Date: 04/26/1996
• Status: Expired due to Fees

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Nakamura, Makibi, Kawaguchi, Naoki, Shimizu, Shuji
• Primary Examiner(s): Christensen, Andrew B.
• Application Number:
  US08/847,747
• Time in Patent Office: 1,785 Days
• Field of Search: 348/234, 348/235, 348/606, 348/607, 348/618, 348/625, 348/362, 348/363, 348/222, 382/266
• US Class Current: 348/222.1
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene
• CPC Class Codes: H04N 23/75 by influencing optical camera components
• CPC Class Codes: H04N 5/142 Edging; Contouring
• CPC Class Codes: H04N 5/52 Automatic gain control

Abstract

An image which is seen as a natural feeling can be attained in such a manner that a resolution of a photographed image is kept substantially constant irrespective of any variation in condition of an optical system such as an iris diaphragm diameter and a zoom position. For example, in the case that it is adapted for an iris diaphragm diameter, an MTF corresponding to a variation of an iris diaphragm diameter is measured (FIG. 6A) and then a gain of an output of an aperture control circuit capable of canceling a reduction of high frequency component of the image signal corresponding to the measured MTF (FIG. 6B). Then, an iris diaphragm diameter varied during a photographing operation is detected, a gain set in response to the detected iris diaphragm diameter is applied to the aperture control circuit, thereby a control is carried out such that an amplitude of the high frequency component of the brightness signal (FIG. 6C) being kept substantially constant without having any relation with the iris diaphragm.

Claims

1. An image signal processing method for processing an image signal of a photographed image provided by a photographing device having an optical system including a zoom lens and an iris diaphragm with a light attenuating filter, said method comprising:

isolating a high frequency band of a brightness signal component of said image signal by delaying said brightness signal component to obtain a first delayed signal, delaying said first delayed signal to obtain a second delayed signal, amplifying said first delayed signal relative to said brightness signal component and said second delayed signal, and subtracting said brightness signal component and said second delayed signal from said amplified first signal to obtain an isolated high frequency band of said brightness signal component;

determining a zoom position of said zoom lens and an aperture size of said iris diaphragm, wherein variation of said zoom position and aperture size causes variation of resolution of said image signal, and said variation of resolution caused by the aperture size variation has a local minimum within a range of the aperture size variation;

selecting a gain, corresponding to the determined zoom position and aperture size, from a plurality of gain values stored in a data table memory; and

intensifying said high frequency band at the selected gain, wherein degradation of resolution of said image signal due to said zoom lens and said iris diaphragm with light attenuating filter is corrected, and resolution becomes approximately constant with zoom position and iris diaphragm aperture size variation.

2. An image signal processing method as set forth in claim 1, wherein a variation of state in said optical system is generated in response to an aberration of a lens.

3. An image signal processing device for processing an image signal of a photographed image, said image signal generated by a photographing device having an optical system including a zoom lens and an iris diaphragm with a light attenuating filter, said image signal processing device comprising:

a high pass filter circuit for isolating a high frequency band of a brightness signal component of said image signal, said high pass filter circuit comprising a first delay for delaying said brightness signal component to obtain a first delayed signal, a second delay for delaying said first delayed signal to obtain a second delayed signal, means for amplifying said first delayed signal with respect to each of said brightness signal component and said second delayed signal, and a synthesizer to subtract said brightness signal component and said second delayed signal from said first delayed signal to obtain said isolated high frequency band of said brightness signal component;

a data table memory for storing a plurality of gain values each corresponding to a zoom position of said zoom lens and an aperture size of said iris diaphragm, wherein variation of said zoom position and aperture size causes variation of resolution of said image signal, and said variation of resolution caused by the aperture size variation has a local minimum within a range of the aperture size variation;

a control section adapted to determine a zoom position of said zoom lens and an aperture size of said iris diaphragm, to select a gain value from said plurality of gain values according to the determined zoom position and aperture size; and

a variable gain amplifier for intensifying said high frequency band at the selected gain, wherein degradation of resolution of said image signal due to said zoom lens and said iris diaphragm with light attenuating filter is corrected, and resolution becomes approximately constant with zoom position and iris diaphragm aperture size variation.

4. An image signal processing device as set forth in claim 3, wherein said image signal processing device is constructed such that a variation of resolution of said image signal generated in response to an aberration of a lens is corrected.

5. An image signal processing device as set forth in claim 3, wherein each of said first and second delays is adapted to delay the signal input thereto in synchronism with a clock frequency corresponding to the number of pixels in one horizontal line.

6. An image signal processing device as set forth in claim 3, wherein each of said first and second delays is adapted to delay the signal input thereto in synchronism with a clock frequency corresponding to one horizontal line.

7. An image signal processing device as set forth in claim 3, wherein said iris diaphragm is a two-vane mechanism.

8. An image signal processing device comprising an image signal recording device for recording an image signal of a photographed image, said image signal generated by a photographing device having an optical system including a zoom lens and an iris diaphragm with a light attenuating filter, said image signal processing device comprising:

a high pass filter circuit for isolating a high frequency band of a brightness signal component of said image signal, said high pass filter circuit comprising a first delay for delaying said brightness signal component to obtain a first delayed signal, a second delay for delaying said first delayed signal to obtain a second delayed signal, means for amplifying said first delayed signal with respect to each of said brightness signal component and said second delayed signal, and a synthesizer to subtract said brightness signal component and said second delayed signal from said first delayed signal to obtain said isolated high frequency band of said brightness signal component;

a data table memory for storing a plurality of gain values each corresponding to a position of said zoom lens and an aperture size of said iris diaphragm, wherein variation of said zoom position and aperture size causes variation of resolution of said image signal, and said variation of resolution caused by the aperture size variation has a local minimum within a range of the aperture size variation;

a control section adapted to determine a zoom position of said zoom lens and an aperture size of said iris diaphragm, to select a gain value from said plurality of gain values according to the determined position and aperture size; and

a variable gain amplifier for intensifying said high frequency band at the selected gain, wherein degradation of resolution of said image signal due to said zoom lens and said iris diaphragm with light attenuating filter is corrected, and resolution becomes approximately constant with zoom position and iris diaphragm aperture size variation.

9. An image signal processing method for processing an image signal of a photographed image provided by a photographing device having an optical system including an iris diaphragm with a light attenuating filter, said method comprising:

isolating a high frequency band of a brightness signal component of said image signal by delaying said brightness signal component to obtain a first delayed signal, delaying said first delayed signal to obtain a second delayed signal, amplifying said first delayed signal relative to said brightness signal component and said second delayed signal, and subtracting said brightness signal component and said second delayed signal from said amplified first signal to obtain an isolated high frequency band of said brightness signal component;

determining an aperture size of said iris diaphragm, wherein variation of said aperture size causes variation of resolution of said image signal, and said variation of resolution caused by the aperture size variation has a local minimum within a range of the aperture size variation;

selecting a gain, according to the determined aperture size, from a plurality of gain values stored in a data table memory, each gain value corresponding to an aperture size of said iris diaphragm; and

intensifying said high frequency band at the selected gain, wherein degradation of resolution of said image signal due to said aperture size of said iris diaphragm with light attenuating filter is corrected, and resolution becomes approximately constant with aperture size variation.

10. An image signal processing device for processing an image signal of a photographed image, said image signal generated by a photographing device having an optical system including an iris diaphragm with a light attenuating filter, said device comprising:

a high pass filter circuit for isolating a high frequency band of a brightness signal component of said image signal, said high pass filter circuit comprising a first delay for delaying said brightness signal component to obtain a first delayed signal, a second delay for delaying said first delayed signal to obtain a second delayed signal, means for amplifying said first delayed signal with respect to each of said brightness signal component and said second delayed signal, and a synthesizer to subtract said brightness signal component and said second delayed signal from said first delayed signal to obtain an isolated high frequency band of said brightness signal component;

a data table memory for storing a plurality of gain values each corresponding to an aperture size of said iris diaphragm, wherein variation of said aperture size causes variation of resolution of said image signal, and said variation of resolution caused by the aperture size variation has a local minimum within a range of the aperture size variation;

a control section adapted to determine an aperture size of said iris diaphragm and to select a gain value from said plurality of gain values according to the determined size; and

a variable gain amplifier for intensifying said high frequency band at the selected gain, wherein degradation of resolution of said image signal due to aperture size of the iris diaphragm with light attenuating filter is corrected, and resolution becomes approximately constant with aperture size variation.

11. An image signal processing device comprising an image signal recording device for recording an image signal of a photographed image, said image signal generated by a photographing device having an optical system including an iris diaphragm with a light attenuating filter, said device comprising:

a high pass filter circuit for isolating a high frequency band of a brightness signal component of said image signal, said high pass filter circuit comprising a first delay for delaying said brightness signal component to obtain a first delayed signal, a second delay for delaying said first delayed signal to obtain a second delayed signal, means for amplifying said first delayed signal with respect to each of said brightness signal component and said second delayed signal, and a synthesizer to subtract said brightness signal component and said second delayed signal from said first delayed signal to obtain an isolated high frequency band of said brightness signal component;

a data table memory for storing a plurality of gain values each corresponding to an aperture size of said iris diaphragm, wherein variation of said aperture size causes variation of resolution of said image signal, and said variation of resolution has a local minimum within a range of the aperture size variation;

a control section adapted to determine an aperture size of said iris diaphragm and to select a gain value from said plurality of gain values according to the determined aperture size; and

a variable gain amplifier for intensifying said high frequency band at the selected gain, wherein degradation of resolution of said image signal due to aperture size of the iris diaphragm with light attenuating filter is corrected, and resolution becomes approximately constant with aperture size variation.

12. An image signal processing method for processing an image signal of a photographed image provided by a photographing device having an optical system including a zoom lens and an iris diaphragm with a light attenuating filter, said method comprising:

isolating a high frequency band of a brightness signal component of said image signal;

determining a state of said optical system which is a function of at least a zoom position of said zoom lens and an aperture size of said iris diaphragm, wherein variation of said zoom position and said aperture size causes variation of resolution of said image signal, and said variation of resolution caused by the aperture size variation has a local minimum within a range of the aperture size variation; and

intensifying said high frequency band at a gain which is a function of said optical system state in a manner such that degradation of resolution of said image signal due to said zoom lens and said aperture size of the iris diaphragm with light attenuating filter is corrected, and resolution becomes approximately constant with zoom position and iris diaphragm aperture size variation.

13. An image signal processing device for processing an image signal for a photographed image, said image signal generated by a photographing device having an optical system including at least an iris diaphragm with a light attenuating filter, said image signal processing device comprising:

a memory section storing a plurality of gain values corresponding to an aperture size of said iris diaphragm with light attenuating filter;

a control section determining an aperture size of said iris diaphragm with light attenuating filter, and selecting a gain value in accordance with said determined aperture size; and

a compensation section compensating said image signal using said gain value selected by said control section;

wherein a resolution of said image signal varies in accordance with an aperture size of said iris diaphragm with light attenuating filter, said variation of image signal resolution caused by said aperture size variation exhibits a local minimum within a range of said aperture size variation, and said gain values compensate for said local minimum.

14. The image signal processing device according to claim 13, wherein said compensation section comprises:

a high pass filter circuit isolating a high frequency band of said image signal;

a variable gain amplifier intensifying said high frequency band by said gain value selected at said control section; and

an adder unit adding said intensified high frequency band of said image signal to said image signal.

15. A camera comprising an image signal processing device for processing an image signal for a photographed image, said image signal generated by a photographing device having an optical system including at least an iris diaphragm with a light attenuating filter, said image signal processing device comprising:

a memory section storing a plurality of gain values corresponding to an aperture size of said iris diaphragm with light attenuating filter;

a control section determining an aperture size of said iris diaphragm with light attenuating filter, and selecting a gain value in accordance with said determined aperture size; and

a compensation section compensating said image signal using said gain value selected by said control section;

wherein a resolution of said image signal varies in accordance with an aperture size of said iris diaphragm with light attenuating filter, said variation of image signal resolution caused by said aperture size variation exhibits a local minimum within a range of said aperture size variation, and said gain values compensate for said local minimum.

16. The camera according to claim 15, wherein said compensation section comprises:

a high pass filter circuit isolating a high frequency band of said image signal;

a variable gain amplifier intensifying said high frequency band by said gain value selected at said control section; and

an adder unit adding said intensified high frequency band of said image signal to said image signal.

17. An image signal processing method for processing an image signal for a photographed image, said image signal generated by a photographing device having an optical system including at least an iris diaphragm with a light attenuating filter, said method comprising:

storing a plurality of gain values corresponding to an aperture size of said iris diaphragm with light attenuating filter;

determining an aperture size of said iris diaphragm with light attenuating filter, and selecting a gain value in accordance with said determined aperture size; and

compensating said image signal using said gain value selected;

wherein a resolution of said image signal varies in accordance with an aperture size of said iris diaphragm with light attenuating filter, said variation of image signal resolution caused by said aperture size variation exhibits a local minimum within a range of said aperture size variation, and said gain values compensate for said local minimum.

18. The image signal processing method according to claim 17, wherein said compensating includes:

isolating a high frequency band of said image signal;

intensifying said high frequency band by said gain value selected; and

adding said intensified high frequency band of said image signal to said image signal.

19. Apparatus comprising:

an image signal processing device for processing an image signal for a photographed image, said image signal generated by a photographing device having an optical system including at least an iris diaphragm with a light attenuating filter, said image signal processing device comprising;

a memory section storing a plurality of gain values corresponding to an aperture size of said iris diaphragm with light attenuating filter;

a control section determining an aperture size of said iris diaphragm with light attenuating filter, and selecting a gain value in accordance with said determined aperture size; and

a compensation section compensating said image signal using said gain value selected by said control section;

wherein a resolution of said image signal varies in accordance with an aperture size of said iris diaphragm with light attenuating filter, said variation of image signal resolution caused by said aperture size variation exhibits a local minimum within a range of said aperture size variation, and said gain values compensate for said local minimum.

20. Apparatus according to claim 19, wherein said compensation section comprises:

a high pass filter circuit isolating a high frequency band of said image signal;

a variable gain amplifier intensifying said high frequency band by said gain value selected at said control section; and

an adder unit adding said intensified high frequency band of said image signal to said image signal.