Still video camera with common circuit for color balance and exposure control

• US 4,805,010 A
• Filed: 05/29/1987
• Issued: 02/14/1989
• Est. Priority Date: 05/29/1987
• Status: Expired due to Term

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: Shroyer, Richard A., Nutting, Thomas C.
• Primary Examiner(s): Groody, James J.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/056,628
• Time in Patent Office: 627 Days
• Field of Search: 358/41, 358/29 C, 358/27, 358/29, 358/228, 358/909
• US Class Current: 348/224.1
• CPC Class Codes: H04N 23/72 Combination of two or more compensation controls
• CPC Class Codes: H04N 23/88 for colour balance, e.g. white-balance circuits or colour temperature control

Abstract

A video still camera includes a common integrating circuit for measuring light level in relation to both color balance and exposure control. An exposure photodiode generates an exposure signal from a small sample of image light diverted from the optical section of the camera. Broadly oriented red, green and blue photodiodes generate three color balance signals corresponding to the color characteristics of the illuminant. The photodiodes are selectively multiplexed into the input of the integrating circuit for the measurements. In one embodiment, the exposure photodiode remains connected to the integrating circuit for exposure measurement. The color balance measurement is unaffected because the small photocurrent from the exposure photodiode is effectively swamped by the much larger color photocurrent from a multiplexed color photodiode.

Claims

1. A video camera having a color image sensor responsive to image light from an illuminated subject and a signal processing section for processing a color signal generated by the image sensor, said camera comprising:

exposure sensing means for generating an exposure signal corresponding to the brightness level of the image light directed toward the image sensor;

color balance sensing means for generating one or more color balance signals corresponding to the color characteristics of the light illuminating the subject;

means, having an input, for integrating an input signal in relation to time and generating a control signal therefrom;

means for connecting said exposure sensing means and said color balance sensing means to the input of said integrating means;

means for selectively operating said integrating means in relation to either said exposure sensing means or said color balance sensing means so that said control signal predominantly represents either an integrated exposure signal or an integrated color balance signal; and

means responsive to said control signal for controlling either the exposure of image light upon the image sensor or the color balance of the color signal processed by the signal processing section.

2. A video camera as claimed in claim 1 which includes an optical section for directing the image light toward the image sensor and wherein said exposure sensing means is responsive to a sample of image light diverted from its path toward the image sensor.

3. A video camera as claimed in claim 2 in which said color balance sensing means includes red, green and blue photosensors for generating corresponding photocurrents for the respective regions of the spectrum.

4. A video camera as claimed in claim 1 in which said exposure sensing means comprises a photodiode for generating a photocurrent corresponding to the brightness level of the image light;

said color balance sensing means comprises a plurality of photodiodes, each sensitive to a different region of the spectrum, for generating photocurrents corresponding to respective regions of the spectrum; and

said means for selectively operating said integrating means grounds a selected photodiode so as to provide the corresponding photocurrent to said integrating means.

5. A video camera as claimed in claim 1 in which said means for selectively operating said integrating means interacts with said color balance means to provide one of said color balance signals to be combined with said exposure signal, to combination thereof to be provided as an input signal to said integrating means.

7. A still video camera as claimed in claim 4 in which said color balance sensing means includes at least two separate photosensors and said multiplexer means operates in a predetermined sequence to provide said exposure and said color balance signals from said separate photosensors to said integrating means.

6. A still video camera having an optical section for directing image light from an illuminated subject toward an image sensor and a signal processing section for processing a plurality of color signals derived from the image sensor, said camera comprising:

exposure sensing means for generating an exposure signal corresponding to the brightness of the image light directed toward the sensor;

color balance sensing means for generating a plurality of color balance signals corresponding to the color characteristics of the light illuminating the subject;

means for integrating an input signal in relation to time and generating a control signal therefrom;

multiplexer means for selectively providing either said exposure signal or one of said color balance signals to said integrating means as said input signal thereof; and

means responsive to said control signal for separately controlling the intensity and/or the duration of the image light impinging upon the image sensor and the relative amplitude of the color signals processed by said signal processing section.

8. A still video camera having an optical section for controlling the exposure of an image sensor with image light from an illuminated subject and a signal processing section for converting the output of the image sensor into a plurality of color signals and for processing the color signals in respectively separate channels, said camera comprising:

an exposure photosensor for generating an exposure signal having a photocurrent amplitude corresponding to the brightness of the image light;

a plurality of color balance photosensors for generating a plurality of color balance signals having respective photocurrent amplitudes corresponding to respective color characteristics of the light illuminating the subject;

means for integrating an input signal in relation to time and generating a control signal therefrom;

circuit means connecting said exposure photosensor into the input circuit of said integrating means;

multiplexer means for selectively connecting said color balance photosensors into the input circuit of said integrating means; and

means responsive to said control signal for either controlling the exposure of the image sensor or, in response to a selection by said multiplexer means, for controlling the gain applied to at least one of the color signals.