Exposure control apparatus and method thereof

• US 20020012065A1
• Filed: 04/23/2001
• Published: 01/31/2002
• Est. Priority Date: 04/27/2000
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Watanabe, Toshiaki
• Granted Patent: US 7,023,484 B2
• Time in Patent Office: Days
• US Class Current: 348/364
• CPC Class Codes: H04N 23/71 Circuitry for evaluating the brightness variation
• CPC Class Codes: H04N 23/72 Combination of two or more compensation controls

Abstract

The exposure control apparatus comprises screen divider which divides the screen into a many areas, and high luminance decider which decides, for each area of the screen, whether a main subject having a high luminance exists within that area. Further, average luminance calculator calculates average luminance in that area of the screen which is decided as including the main subject, and exposure value determiner determines the exposure value based on the calculated average luminance.

Claims

1. An exposure control apparatus which determines an exposure value based on the luminance of a photographic screen and performs exposure control based on the determined exposure value, said exposure control apparatus comprising:

an area generating unit which divides the photographic screen into a predetermined number of areas;

a deciding unit which decides, for each area generated by said area generating unit, whether a main subject having a high luminance exists within that area;

an average luminance calculating unit which calculates an average luminance in the area generated by the area generating unit according to the decision result by said deciding unit; and

an exposure value determining unit which determines an exposure value based on the average luminance in the area calculated by said average luminance calculating unit.

2. The exposure control apparatus according to claim 1, wherein said deciding unit counts pixels, each having a luminance higher than a predetermined luminance threshold, out of pixels forming the area and decides whether the count value of the high luminance pixels exceeds a predetermined count threshold;

and

said average luminance calculating unit calculates the average luminance by using the luminance per se of the high luminance pixel when the deciding unit decides that the high luminance pixel count value exceeds the predetermined count threshold;

in contrast, said average luminance calculating unit substitutes a predetermined low luminance smaller than the predetermined luminance threshold for the luminance of the high luminance pixel so as to calculate the average luminance when the deciding unit decides that the high luminance pixel count value is equal to or smaller than the predetermined count threshold.

3. The exposure control apparatus according to claim 2, further comprising a parameter table which stores therein a plurality of parameter groups, each of which includes the luminance threshold, the count threshold and the low luminance,

wherein said deciding unit and said average luminance calculating unit select the parameter group according to an exposure condition.

4. The exposure control apparatus according to claim 3, wherein the parameter group per area generated by said area generating unit is stored in the parameter table, and said deciding unit and said average luminance calculating unit select the parameter group according to the area generated by said area generating unit.

5. The exposure control apparatus according to claim 3, wherein said parameter table stores the plurality of low luminances in the parameter groups, and said average luminance calculating unit selects the low luminance according to the high luminance pixel count value.

6. The exposure control apparatus according to claim 4, wherein said parameter table stores the plurality of low luminances in the parameter groups, and said average luminance calculating unit selects the low luminance according to the high luminance pixel count value.

7. The exposure control apparatus according to claim 3, wherein said parameter table stores the plurality of count thresholds in the parameter groups, and said deciding unit selects the count value according to the exposure condition.

8. The exposure control apparatus according to claim 4, wherein said parameter table stores the plurality of count thresholds in the parameter groups, and said deciding unit selects the count value according to the exposure condition.

9. An exposure control apparatus comprising:

an area generating unit which divides a screen into a predetermined number of areas;

a deciding unit which decides in which area of the screen a subject having a high luminance is included;

an average luminance calculating unit which calculates an average luminance in that area of the screen which said deciding unit decides as including the subject; and

an exposure value determining unit which determines an exposure based on the average luminance calculated by said average luminance calculating unit.

10. An exposure control method which determines an exposure value based on the luminance of a photographic screen and performs exposure control based on the determined exposure value, said exposure control apparatus comprising:

an area generating step which divides the photographic screen into a predetermined number of areas;

a deciding step which decides, for each area generated by said area generating step, whether a main subject having a high luminance exists within that area;

an average luminance calculating step which calculates an average luminance in the area generated by the area generating step according to the decision result by said deciding step; and

an exposure value determining step which determines an exposure value based on the average luminance in the area calculated by said average luminance calculating step.

11. The exposure control method according to claim 10, wherein said deciding step counts pixels, each having a luminance higher than a predetermined luminance threshold, out of pixels forming the area and decides whether the count value of the high luminance pixels exceeds a predetermined count threshold;

and

said average luminance calculating step calculates the average luminance by using the luminance per se of the high luminance pixel when the deciding step decides that the high luminance pixel count value exceeds the predetermined count threshold;

in contrast, said average luminance calculating step substitutes a predetermined low luminance smaller than the predetermined luminance threshold for the luminance of the high luminance pixel so as to calculate the average luminance when the deciding step decides that the high luminance pixel count value is equal to or smaller than the predetermined count threshold.