Automatic exposure control apparatus

An automatic exposure control apparatus comprising:

• state judgment means for judging whether an image frame is in a backlight state or in an excessive frontlight state based on a spatial luminance pattern of said image frame;
• image frame luminance calculation means for calculating an average luminance of said image frame;
• region luminance calculation means for calculating average luminances of a plurality of regions, said plurality of regions constituting said image frame;
• first select region luminance calculation means for arranging said average luminances of said plurality of regions obtained by said region luminance calculation means in luminance order such that said average luminances are arranged in at least one of ascending and descending order, for selecting at least one of said plurality of regions by identifying a predefined range in said luminance order and selecting the at least one of said plurality of regions from said plurality of regions which have a corresponding average luminance that is within the predefined range in said luminance order, and for calculating an average value of said average luminances of said selected at least one region;
• second select region luminance calculation means for arranging said average luminances obtained by said region luminance calculation means in luminance order such that said average luminances are arranged in at least one of ascending and descending order, for selecting at least one of said plurality of regions by identifying a predefined range in said luminance order and selecting the at least one of said plurality of regions from said plurality of regions which have a corresponding average luminance that is within the predefined range in said luminance order, and for calculating an average value of said average luminances of said selected at least one region;
• backlight degree calculation means for calculating a first value representing a degree of backlighting in said image frame as a function of said average value obtained by said first select region luminance calculations means;
• excessive frontlight degree calculation means for calculating a second value representing an excessive degree of frontlighting of said image frame as a function of said average value obtained by said second select region luminance calculation means;
• correction amount determination means for determining a correction amount based on the judgment result by said state judgment means, said first value and said second value;
• target luminance calculation means for calculating a target average luminance for an exposure correction based on said correction amount;
• and
• exposure correction means for correcting an exposure so that said average luminance obtained by said image frame luminance calculation means is kept substantially equal to said target average luminance.

An automatic exposure control apparatus comprising:

• state judgment means for judging whether an image frame is in a backlight state or in an excessive frontlight state;
• image frame luminance calculation means for calculating an average luminance of said image frame;
• region luminance calculation means for calculating average luminances of a plurality of regions, said plurality of regions constituting said image frame;
• first select region luminance calculation means for arranging said average luminances of said plurality of regions obtained by said region luminance calculation means in luminance order such that said average luminances are arranged in at least one of ascending and descending order, for selecting at least one of said plurality of regions by identifying a predefined range in said luminance order and selecting the at least one of said plurality of regions from said plurality of regions which have a corresponding average luminance that is within the predefined range in said luminance order, and for calculating an average value of said average luminances of said selected at least one region;
• second select region luminance calculation means for arranging said average luminances obtained by said region luminance calculation means in luminance order such that said average luminances are arranged in at least one of ascending and descending order, for selecting at least one of said plurality of regions by identifying a predefined range in said luminance order and selecting the at least one of said plurality of regions from said plurality of regions which have a corresponding average luminance that is within the predefined range in said luminance order, and for calculating an average value of said average luminances of said selected at least one region;
• backlight degree calculation means for calculating a first value representing a degree of backlighting in said image frame as a function of said average value obtained by said first select region luminance calculations means;
• excessive frontlight degree calculation means for calculating a second value representing an excessive degree of frontlighting of said image frame as a function of said average value obtained by said second select region luminance calculation means;
• correction amount determination means for determining a correction amount based on the judgment result by said state judgment means, said first value and said second value;
• target luminance calculation means for calculating a target average luminance for an exposure correction based on said correction amount;
• and
• exposure correction means for correcting an exposure so that said average luminance obtained by said image frame luminance calculation means is kept substantially equal to said target average luminance,
• wherein said image frame includes a first upper region and a lower region;
• said image frame also includes a lower central region, a second upper region, a left region and a right region;
• said automatic exposure control apparatus further includes indoor/outdoor judgment means for judging whether the image frame is indoors or outdoors;
• said state judgment means includes:
• (a) first/second region comparison means for comparing an average luminance of a first region with an average luminance of a second region and for generating a first judgment value indicating the result of the comparison,
• (b) upper/lower region comparison means for comparing an average luminance of said first upper region with an average luminance of said lower region and for generating a second judgment value indicating the result of the comparison,
• (c) select means for selecting one of said first judgment value and said second judgment value according to the result of judgment by said indoor/outdoor judgment means, and
• (d) judgment means for judging whether said image frame is in a backlight state or in an excessive frontlight state based on said selected judgment value;
• wherein, said first region is a combination of said second upper region with one of said left region and said right region, which has a higher average luminance than the other, and said second region is a combination of said lower central region with one of said left region and said right region, which has a lower average luminance than the other.