Televison camera

• US 5,293,238 A
• Filed: 06/16/1992
• Issued: 03/08/1994
• Est. Priority Date: 06/24/1991
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Nakano, Takahiro, Imaide, Takuya
• Primary Examiner(s): Razavi, Michael T.
• Assistant Examiner(s): Ho, Tuan V.
• Application Number:
  US07/899,250
• Time in Patent Office: 630 Days
• Field of Search: 358/213.18, 358/213.15, 358/213.19, 358/167
• US Class Current: 348/226.1
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene
• CPC Class Codes: H04N 23/72 Combination of two or more compensation controls
• CPC Class Codes: H04N 23/745 Detection of flicker frequency or suppression of flicker wherein the flicker is caused by illumination, e.g. due to fluorescent tube illumination or pulsed LED illumination
• CPC Class Codes: Y10S 348/91 Flicker reduction

Abstract

Flicker which occurs when a television camera images an object under illumination of a flickering light source such as fluorescent lamp is minimized without causing sensitivity of a photoelectric conversion element and hence the camera to be degraded under a non-flickering light source. The television camera includes an automatic iris control device, an automatic gain control circuit, a microcomputer, a photoelectric conversion element and an integration circuit for integrating output signal of the photoelectric conversion element for each field period. The microcomputer sets a signal storage time of the photoelectric conversion element to a value by which flicker noise can be restricted when flicker is detected on the basis of a change of an output signal of the integration circuit and sets it to another value when a change of light source is detected on the basis of a change of iris value and gain.

Claims

1. In a television camera having an optical system, an iris device, an automatic iris control device for automatically controlling opening of said iris device, a photoelectric conversion element for converting an optical image obtained through said optical system and said iris device into an electric signal, an automatic gain control device for controlling gain of the electric signal, a first detection means responsive to flickering in the electric signal at an output of said photoelectric conversion element for detecting flickering at a flickering frequency of a first illumination light source, each half cycle of the flickering frequency defining a flickering period, a signal storage time control means for controlling a signal storage time of said photoelectric conversion element such that in response to the first detection means detecting the flickering, the signal storage time is controlled to become an integer multiple of the flickering period of said first light source, whereby changing the signal storage time to an integer multiple of the flickering period substantially eliminates flicker in the electric signal at the output of the photoelectric conversion element, THE IMPROVEMENT COMPRISING:

a second detection means including;

a means for storing a current iris value in response to the first detection means detecting the flickering frequency, current iris values with the stored iris value, and

a means connected with the signal storage time control means for causing the signal storage time control means to change the signal storage time of said photoelectric conversion element from the integer multiple of the flickering period to a predetermined time different from the time which is the integer multiple of the flickering period when said comparing means detects a change in the iris value above a preselected minimum change indicative of a switching of said first light source to another light source.

2. The television camera claimed in claim 1, wherein said first detection means comprises an integration circuit for integrating a whole or a portion of the output signal from said photoelectric conversion element for each field period and a control and processing device responsive to an output from said integration circuit to operate, store and compare a difference in signal intensity between adjacent field periods.

3. The television camera claimed in claim 1, wherein said second detection means comprises a control and processing device responsive to an iris value of said automatic iris control device and a gain value of said automatic gain control device to store an iris value and a gain value when said first detection means detects the flickering frequency of said light source and to detect changes of iris value and gain from said stored iris value and gain value by amounts exceeding certain constant values, respectively.

4. In a television camera having an optical system, an iris device, an automatic iris control device for automatically controlling opening of said iris device, a photoelectric conversion element for converting an optical image obtained through said optical system and said iris device into an electric signal, a first detection means responsive to flickering in the electric signal at an output of said photoelectric conversion element for detecting flickering at a flickering frequency of a first illumination light source, each half cycle of the flickering frequency defining a flickering period, a signal storage time control means for controlling a signal storage time of said photoelectric conversion element such that in response to the first detection means detecting the flickering, the signal storage time is controlled to become an integer multiple of the flickering period of said firs light source, whereby changing the signal storage time to an integer multiple of the flickering period substantially eliminates flicker in the electric signal at the output of the photoelectric conversion element, THE IMPROVEMENT COMPRISING:

a second detection means including;

a means for storing a color temperature information value in response to said first detection means detecting the flickering frequency,

a means for comparing subsequent color temperature information values with said stored color temperature information, and

a means connected with the signal storage time control means for causing the signal storage time control means to change the signal storage time of said photoelectric conversion element from the integer multiple of the flickering period to a predetermined time different from the integer multiple of the flickering period in response to said comparing means detecting the change of color temperature information values exceeding a preselected minimum change indicative of a switching from said first light source to another light source.

5. A television camera having flicker noise restriction capability, which camera includes a lens system, an iris device, a photoelectric conversion element disposed behind said iris device for converting an optical image received through said lens system and said iris device into an electric signal, an iris control device, a variable gain circuit for regulating gain of said photoelectric conversion element and a signal processing circuit for processing the electric signal from said photoelectric conversion element to obtain a television signal, said television camera comprising:

first means responsive to an output signal of said signal processing circuit to supplying control signals for controlling said iris control device and said variable gain circuit;

an integrater circuit for integrating the television signal for a time corresponding to one field period and sampling and holding an integrated television signal every field;

second means responsive to an output of said integrater circuit for determining whether or not there is flicker noise;

third means for regulating signal storage time of said photoelectric conversion element to 1/100 sec and storing an iris value and a gain when said second means determines existence of flicker noise;

fourth means responsive to an iris value and a gain for determining whether or not there is any change in iris value and gain when said second means determines absence of flicker noise;

fifth means for changing signal storage time of said photoelectric conversion element to 1/60 sec when said fourth means determines an existence of change of iris value and gain.