IMAGE CAPTURING APPARATUS, IMAGE CAPTURING METHOD, EXPOSURE CONTROL METHOD, AND PROGRAM

• US 20080266424A1
• Filed: 03/26/2008
• Published: 10/30/2008
• Est. Priority Date: 04/24/2007
• Status: Active Grant

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Asoma, Akira
• Granted Patent: US 7,948,538 B2
• Time in Patent Office: Days
• US Class Current: 348/234
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene
• CPC Class Codes: H04N 23/73 by influencing the exposure time
• CPC Class Codes: H04N 23/741 by increasing the dynamic range of the image compared to the dynamic range of the electronic image sensors

Abstract

An image capturing apparatus includes: an image capturing unit configured to generate a long-exposure image signal and a short-exposure image signal on the basis of light transmitted from a subject and output the long-exposure image signal and the short-exposure image signal as image capturing signals; a signal processing unit configured to generate a combined image signal by combining the long-exposure image signal and the short-exposure image signal, the combined image signal having a dynamic range that is relatively wider than that of at least any one of the long-exposure image signal and the short-exposure image signal; a detection unit configured to generate luminance information of the combined image signal; and a control unit configured to perform automatic exposure control for the short-exposure image signal using the luminance information in an exposure setting mode in which exposure control is performed in accordance with a user'"'"'s setting.

Claims

1. An image capturing apparatus comprising:

an image capturing unit configured to generate a long-exposure image signal and a short-exposure image signal on the basis of light transmitted from a subject and output the long-exposure image signal and the short-exposure image signal as image capturing signals, the long-exposure image signal being generated by exposure for a relatively long period and the short-exposure image signal being generated by exposure for a relatively short period;

a signal processing unit configured to generate a combined image signal by combining the long-exposure image signal and the short-exposure image signal, the combined image signal having a dynamic range that is relatively wider than that of at least any one of the long-exposure image signal and the short-exposure image signal;

a detection unit configured to generate luminance information of the combined image signal; and

a control unit configured to perform automatic exposure control for the short-exposure image signal using the luminance information in an exposure setting mode in which exposure control is performed in accordance with a user'"'"'s setting.

2. The image capturing apparatus according to claim 1,

wherein the detection unit generates a luminance histogram as the luminance information, and

wherein the control unit detects occurrence of overexposure in the combined image signal using the luminance histogram, sets a short-exposure period on the basis of a detection result, and performs the automatic exposure control for the short-exposure image signal using the short-exposure period.

3. The image capturing apparatus according to claim 1, wherein the control unit sets a new short-exposure period by performing computation using a current short-exposure period and a fixed value.

4. The image capturing apparatus according to claim 1, wherein the control unit calculates a percentage of a desired luminance level region to a whole luminance level region in the combined image signal, and sets the new short-exposure period on the basis of a relationship between the percentage and a convergence target value.

5. The image capturing apparatus according to claim 2,

wherein the detection unit classifies luminance levels into a black level, an intermediate luminance level, and a white level and generates information about a distribution of these luminance levels as the luminance histogram, and

wherein the control unit uses information about the intermediate luminance level for setting of the short-exposure period.

6. An image capturing method comprising the steps of:

generating a long-exposure image signal by exposure for a relatively long period and a short-exposure image signal by exposure for a relatively short period on the basis of light transmitted from a subject in an exposure setting mode in which exposure control is performed in accordance with a user'"'"'s setting so as to output the long-exposure image signal and the short-exposure image signal as image capturing signals;

generating a combined image signal by combining the long-exposure image signal and the short-exposure image signal, the combined image signal having a dynamic range that is relatively wider than that of at least any one of the long-exposure image signal and the short-exposure image signal;

generating luminance information of the combined image signal; and

performing automatic exposure control for the short-exposure image signal using the luminance information.

7. An exposure control method that is performed in an exposure setting mode in which exposure control is performed in accordance with a user'"'"'s setting and is performed by an image capturing apparatus for obtaining a long-exposure image signal by exposure for a relatively long period and a short-exposure image signal by exposure for a relatively short period, generating a combined image signal with a dynamic range that is relatively wider than that of at least any one of the long-exposure image signal and the short-exposure image signal by combining the long-exposure image signal and the short-exposure image signal, and outputting the generated combined image signal, the exposure control method comprising the steps of:

obtaining luminance information of the combined image signal;

detecting occurrence of overexposure in the combined image signal using the luminance information;

setting a short-exposure period on the basis of a detection result of the occurrence of the overexposure; and

performing exposure control for the short-exposure image signal using the short-exposure period.

8. A program causing a computer to perform an exposure control method that is performed in an exposure setting mode in which exposure control is performed in accordance with a user'"'"'s setting and is performed by an image capturing apparatus for obtaining a long-exposure image signal by exposure for a relatively long period and a short-exposure image signal by exposure for a relatively short period, generating a combined image signal with a dynamic range that is relatively wider than that of at least any one of the long-exposure image signal and the short-exposure image signal by combining the long-exposure image signal and the short-exposure image signal, and outputting the generated combined image signal, the exposure control method comprising the steps of:

obtaining luminance information of the combined image signal;

detecting occurrence of overexposure in the combined image signal using the luminance information;

setting a short-exposure period on the basis of a detection result of the occurrence of the overexposure; and

performing exposure control for the short-exposure image signal using the short-exposure period.