Digital camera with sensitivity compensation

• US 7,336,308 B2
• Filed: 02/27/2003
• Issued: 02/26/2008
• Est. Priority Date: 03/06/2002
• Status: Expired due to Fees

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Inventors: Kubo, Naoki
• Primary Examiner(s): Ye; Lin
• Assistant Examiner(s): LAM, HUNG H
• Application Number:
  US10/374,047
• Publication Number:
  US 20030169357A1
• Time in Patent Office: 1,825 Days
• Field of Search: 348/296, 348/229.1, 348/277
• US Class Current: 348/296
• CPC Class Codes: H04N 23/673 based on contrast or high frequency components of image signals, e.g. hill climbing method
• CPC Class Codes: H04N 23/73 by influencing the exposure time
• CPC Class Codes: H04N 23/76 by influencing the image signals
• CPC Class Codes: H04N 23/84 for processing colour signals

Abstract

Voltage signals outputted from a CCD are subjected to correlated double sampling processing by a correlated double sampling circuit (CDS), after which digital gain processing is carried out at a gain control amplifier (GCA). A gain difference between G color signals and R/B color signals outputted from the CCD is caused by a difference between a G exposure duration t_G and an R/B exposure duration t_R/B. When the value of a ratio between the t_G and the t_R/B falls below a predetermined value, the GCA applies digital gain for compensating for the gain difference by multiplying respective signal values of R, G and B by gain correction coefficients as follows: (gain compensation coefficient α)=(G exposure duration t_G)/(R/B exposure duration t_R/B)=(G exposure duration t_G)/((G exposure duration t_G)+(exposure duration difference Δt)).

Claims

1. A digital camera comprising:

solid state imaging elements which receive light in accordance with a subject image, and accumulate charge in accordance with the received light, the solid state imaging elements being divided into two regions, one region being covered by color-separation filters transmitting a green-color light and another region being covered by color-separation filters transmitting one of a red-color and a blue-color light;

an electronic shutter;

a shutter pulse output section which, after the electronic shutter resets charges in all of the solid state imaging elements at the same time, outputs a first shutter pulse and a second shutter pulse at mutually different times;

an imaging control section which controls such that accumulated charges of solid state imaging elements corresponding to the green-color light are read out on the basis of edge timing of the first shutter pulse and accumulated charges of solid state imaging elements corresponding to the one of the red-color and the blue-color light are read out on the basis of edge timing of the second shutter pulse; and

a compensation section which performs gain compensation on the basis of a value of a ratio between charge accumulation durations of the region covered by color-separation filters transmitting a green-color light and the region covered by color-separation filters transmitting one of a red-color and a blue-color light, such that gains for the respective regions are mutually equal.

2. The digital camera of claim 1, wherein, when the value of the ratio between the charge accumulation durations of the region covered by color-separation filters transmitting a green-color light and the region covered by color-separation filters transmitting one of a red-color and a blue-color light is less than or equal to a predetermined value, the compensation section performs the compensation using a compensation coefficient which is determined in advance on the basis of a difference between the charge accumulation durations of the region covered by color-separation filters transmitting a green-color light and the region covered by color-separation filters transmitting one of a red-color and a blue-color light.

3. The digital camera of claim 1, further comprising a mechanical shutter section which physically shields light irradiating toward a light-receiving surface of the solid state imaging elements, wherein the gain compensation by the compensation section is not implemented when the mechanical shutter is operated.

4. The digital camera of claim 2, further comprising a mechanical shutter section which physically shields light irradiating toward a light-receiving surface of the solid state imaging elements, wherein the gain compensation by the compensation section is not implemented when the mechanical shutter is operated.

13. The digital camera of claim 1, wherein the solid state imaging elements are a honeycomb CCD.

5. A digital camera comprising:

an optical unit which includes a lens for focusing a subject image, a shutter, an aperture mechanism, a focus point adjustment motor, and a zoom motor;

a CCD (charge-coupled-device) where all pixels are divided into two regions, one region being covered by color-separation filters transmitting a green-color light and another region being covered by color-separation filters transmitting one of a red-color light and a blue-color light;

a signal-processing section which generates digital image data representing the subject image on the basis of output signals from the CCD, and which generates timing signals for driving the optical unit and the CCD;

an electronic shutter;

a shutter pulse output section that, after the electronic shutter resets charges in all the pixels of the CCD at the same time, outputs a first shutter pulse and a second shutter pulse at different times;

a main control section which controls overall operation of the digital camera;

a vertical/horizontal driver which drives the CCD;

a shutter/iris motor driver which drives the shutter and the aperture mechanism;

a focus motor driver which drives the focus point adjustment motor; and

a zoom motor driver which drives the zoom motor, wherein accumulated charges of pixels of the CCD corresponding to the green-color light are read out on the basis of edge timing of the first shutter pulse and accumulated charges of pixels of the CCD corresponding to the one of the red-color and the blue-color light are read out on the basis of edge timing of the second shutter pulse, and

the signal-processing section includes a compensation section which performs gain compensation on the basis of a value of a ratio between charge accumulation durations of the region covered by color-separation filters transmitting a green-color light and the region covered by color-separation filters transmitting one of a red-color and a blue-color light, such that gains for the respective regions are mutually equal.

6. The digital camera of claim 5, further comprising:

RAM for storing the digital image data;

ROM for storing parameters and programs;

an image display section which displays the subject image and information; and

a power supply section which supplies electrical power to the main control section.

7. The digital camera of claim 5, wherein the signal-processing section further comprises a correlated double sampling circuit, an A/D converter, and a timing generator.

8. The digital camera of claim 5, wherein the main control section comprises a bus which interconnects between:

a CPU which controls overall operation of the main control section;

a built-in line buffer with a predetermined capacity;

an imaging control section which includes a white balance adjustment circuit for adjusting changes of white balance and a Y/C conversion circuit for converting RGB data to YC signals;

a compression/decompression section which carries out compression processing to a predetermined compression format on the digital image data, and carries out decompression processing on digital image data that has been compression-processed;

a media control section;

an image display control section; and

a video encoder.

9. The digital camera of claim 8, wherein a removable recording medium is connected to the media control section.

10. The digital camera of claim 8, wherein an image display section is connected to the image display control section.

11. The digital camera of claim 8, wherein an output terminal of the CCD is connected to the imaging control section via a correlated double sampling circuit, a gain control amplifier and an A/D converter, in that order.

12. The digital camera of claim 5, wherein an input terminal of the focus motor driver and an input terminal of the zoom motor driver are respectively connected to the main control section, an output terminal of the focus motor driver is connected to the focus point adjustment motor, and an output terminal of the zoom motor driver is connected to the zoom motor.

14. The digital camera of claim 5, wherein the CCD is a honeycomb CCD.