Image binarization apparatus, image binarization method, image pickup apparatus, image pickup method, and a computer product

An image binarization apparatus comprising:

• a block division unit which divides a multi-valued image into blocks;
• a luminance value output unit which outputs a luminance value of each pixel forming the multi-valued image;
• a binarization threshold value setting unit which sets a binarization threshold value to be used when binarizing the multi-valued image;
• a low luminance threshold value setting unit which sets a low luminance threshold value to be used when removing low luminance values;
• a low luminance value removal unit which inputs luminance values of each pixel from among luminance values output by said luminance value output unit, removes luminance values that are lower than the low luminance threshold value set by said low luminance threshold value setting unit, and outputs only those luminance values which exceed the low luminance threshold value;
• a mean luminance value calculation unit which calculates a mean luminance value of the luminance values output by said low luminance value removal unit;
• a block binarization threshold value setting unit which sets a block binarization threshold value which is a binarization threshold value applied to at least selected of the blocks based on the mean luminance values calculated by said mean luminance value calculation unit;
• and
• an interpolation block setting unit for setting interpolation blocks which cover pixels extending over two or more adjacent of the selected of the blocks,
• wherein said low luminance threshold value setting unit sets the low luminance threshold value based on mean luminance values of the two or more adjacent of the selected of the blocks;
• and
• said binarization threshold value setting unit sets the binarization threshold value to be applied to pixels inside the interpolation block based on block binarization threshold values of each of the two or more adjacent of the selected of the blocks bridged by the interpolation block.

An image binarization apparatus comprising:

• a block division unit which divides a multi-valued image into blocks;
• a luminance value output unit which outputs a luminance value of each pixel forming the multi-valued image;
• a binarization threshold value setting unit which sets a binarization threshold value to be used when binarizing the multi-valued image;
• a mean luminance value calculation unit which receives luminance values of each pixel forming at least selected of the blocks from among luminance values output by said luminance value output unit, and calculates mean luminance values of the selected of the blocks;
• and
• a luminance value limiting unit which limits a range of mean luminance values calculated by said mean luminance value calculation unit so that the values are within a predetermined spread,
• wherein said binarization threshold value setting unit sets binarization threshold values of the selected of the blocks based on the mean luminance values the range of which is limited by said luminance value limiting unit.

An image binarization apparatus comprising:

• a block division unit which divides a multi-valued image into blocks;
• a luminance value output unit which outputs a luminance value of each pixel forming the multi-valued image;
• binarization threshold value setting unit which sets a binarization threshold value to be used when binarizing the multi-valued image;
• a mean luminance value calculation unit which receives luminance values of each pixel forming at least selected of the blocks from among luminance values output by said luminance value output unit, and calculates mean luminance values of the selected of the blocks;
• a luminance value limiting unit which limits a range of the mean luminance values calculated by said mean luminance value calculation unit so that the values are within a predetermined spread;
• a block binarization threshold value setting unit which sets a block binarization threshold value which is a binarization threshold value applied to the selected of the blocks based on the mean luminance values calculated by said mean luminance value calculation unit;
• and
• an interpolation block setting unit which sets interpolation blocks which cover pixels extending over two or more adjacent of the selected of the blocks,
• wherein said binarization threshold value setting unit sets binarization threshold values applied to pixels inside the interpolation block based on block binarization threshold values of each of the two or more adjacent of the selected of the blocks bridged by the interpolation block.

An image pickup apparatus comprising:

• an image pickup unit which picks up an image of an object of a photograph;
• a screen division unit which divides the photographed object into a plurality of Screens;
• a photometry unit which measures light of screens created by said screen division unit;
• a block division unit which divides a multi-valued image picked up by said image pickup unit into blocks;
• a binarization threshold value setting unit which sets binarization threshold values used when binarizing the multi-valued image;
• and
• a photometric value limiting unit which limits a spread of photometric values measured by said photometry unit so that the values are within a predetermined range,
• wherein said binarization threshold value setting unit sets binarization threshold values of blocks created by said block division unit based on photometric values the range of which has been limited by said photometric value limiting unit.

An image pickup apparatus comprising:

• an image pickup unit which picks up an image of an object of a photograph;
• a screen division unit which divides the object being photographed into a plurality of screens;
• a photometry unit which measures light of screens created by said screen division unit;
• a block division unit which divides a multi-valued image picked up by said image pickup unit into blocks;
• a binarization threshold value setting unit which sets binarization threshold values used when binarizing the multi-valued image;
• a photometric value limiting unit which limits a spread of photometric values measured by said photometry unit so that the values are within a predetermined range;
• and
• an interpolation block setting unit which sets interpolation blocks which cover an image area extending over two or more adjacent screens from among the screens created by said screen division unit,
• wherein said binarization threshold value setting unit sets binarization threshold values to be applied to pixels within the interpolation blocks based on photometric values the range of each of which has been limited of the two or more screens bridged by the interpolation block.

A computer readable medium for storing instructions, which when executed by a computer, causes the computer to perform an image binarization method comprising:

• a block division in which the multi-valued image is divided into blocks;
• a low luminance threshold value setting in which a low luminance threshold value to be used when removing low luminance values is set based on mean luminance values of adjacent of at least selected of the blocks;
• a low luminance value removal in which luminance values below the low luminance threshold value are removed from among luminance values of pixels contained in the selected of the blocks and only luminance values which exceed the low luminance threshold value are output;
• a mean luminance value calculation in which luminance values output in the low luminance value removal are input and mean luminance values of the selected of the blocks are calculated;
• and
• a binarization threshold value setting in which binarization threshold values to be used in binarization processing of the selected of the blocks are set based on mean luminance values of the selected of the blocks calculated in the mean luminance value calculation.

A computer readable medium for storing instructions, which when executed by a computer, causes the computer to perform an image binarization method comprising:

• a block division in which the multi-valued image is divided into blocks;
• a low luminance threshold value setting in which a low luminance threshold value to be used when removing low luminance values is set based on mean luminance values of adjacent of at least selected of the blocks;
• a low luminance value removal in which luminance values below the low luminance threshold value are removed from among luminance values of pixels contained in the selected of the blocks and only luminance values which exceed the low luminance threshold value are output;
• a mean luminance value calculation in which luminance values output in the low luminance value removal are input and mean luminance values of the selected of the blocks are calculated;
• a block binarization threshold value setting in which a block binarization threshold value which is a binarization threshold value applied to a block is set based on a mean luminance value calculated in the mean luminance value calculation;
• an interpolation block setting in which interpolation blocks which cover pixels extending over two or more adjacent of the selected of the blocks are set;
• and
• a binarization threshold value setting in which binarization threshold values to be applied to pixels within the interpolation blocks are set based on each block binarization threshold value of the two or more adjacent of the selected blocks bridged by the interpolation block set in the interpolation block setting.

A computer readable medium for storing instructions, which when executed by a computer, causes the computer to perform an image binarization method comprising:

• a block division in which the multi-valued image is divided into blocks;
• a mean luminance value calculation in which mean luminance values of at least selected of the blocks are calculated;
• a luminance value limiting in which a spread of mean luminance values calculated in the mean luminance value calculation is limited so that the values are within a predetermined range;
• and
• a binarization threshold value setting in which binarization threshold value to be used in binarization processing of the selected of the blocks is set based on mean luminance values the range of which has been limited in the luminance value limiting.

A computer readable medium for storing instructions, which when executed by a computer, causes the computer to perform an image binarization method comprising:

• a block division in which the multi-valued image is divided into blocks;
• a mean luminance value calculation in which mean luminance values of at least selected of the blocks are calculated;
• a luminance value limiting in which a spread of mean luminance values calculated in the mean luminance value calculation is limited so that the values are within a predetermined range;
• a block binarization threshold value setting in which a block binarization threshold value which is a binarization threshold value applied to the at least selected of the blocks is set based on mean luminance values the range of which has been limited in the mean luminance value limiting;
• an interpolation block setting in which interpolation blocks which share pixels extending over two or more adjacent of the selected of the blocks are set;
• and
• a binarization threshold value setting in which binarization threshold values to be applied to pixels within the interpolation blocks are set based on each block binarization threshold value of the two or more adjacent of the selected of the blocks bridged by the interpolation block set in the interpolation block setting.

A computer readable medium for storing instructions, which when executed by a computer, causes the computer to perform an image pickup method comprising:

• a screen division in which an object of a photograph is divided into a plurality of screens;
• a photometry in which light of screens created in the screen division is measured;
• an image pickup in which an image of the object of the photograph is picked up;
• a block division in which a multi-valued image which was picked up in the image pickup is divided into blocks;
• a photometric value smoothing in which photometric values measured in the photometry are smoothed;
• and
• a binarization threshold value setting in which binarization threshold values of at least selected of the blocks are set based on photometric values smoothed in the photometric value smoothing.

A computer readable medium for storing instructions, which when executed by a computer, causes the computer to perform an image pickup method comprising:

• a screen division in which an object of a photograph is divided into a plurality of screens;
• a photometry in which light of screens created in the screen division is measured;
• an image pickup in which an image of the object of the photograph is picked up;
• a block division in which a multi-valued image which was picked up in the image pickup is divided into blocks;
• a photometric value smoothing in which photometric values measured in the photometry are smoothed;
• an interpolation block setting in which interpolation blocks which cover an image area extending over two or more adjacent screens are set from among the screens created in the screen division;
• and
• a binarization threshold value setting in which binarization threshold values applied to pixels within the interpolation blocks are set based on smoothed photometric values of each of the two or more screens bridged by the interpolation blocks set in the interpolation block setting.

A computer readable medium for storing instructions, which when executed by a computer, causes the computer to perform an image pickup method comprising:

• a screen division in which an object of a photograph is divided into a plurality of screens;
• a photometry in which light of screens created in the screen division is measured;
• an image pickup in which an image of the object of the photograph is picked up;
• a block division in which a multi-valued image which was picked up in the image pickup is divided into blocks;
• a photometric value limiting in which the spread of photometric values measured in the photometry is limited so that the values are within a predetermined range;
• and
• a binarization threshold value setting in which binarization threshold values of the at least selected of blocks are set based on photometric values whose range has been limited in the photometric value limiting.

computer readable medium for storing instructions, which when executed by a computer, causes the computer to perform an image pickup method comprising:

• a screen division in which an object of a photograph is divided into a plurality of screens;
• a photometry in which light of screens created in the screen division is measured;
• an image pickup in which an image of the object of the photograph is picked up;
• a block division in which a multi-valued image which was picked up in the image pickup is divided into blocks;
• a photometric value limiting in which the spread of photometric values measured in the photometry is limited so that the values are within a predetermined range;
• an interpolation block setting in which interpolation blocks which cover an image area extending over two or more adjacent screens are set from among the screens created in the screen division;
• and
• a binarization threshold value setting in which binarization threshold values applied to pixels within the interpolation blocks are set based on photometric values the range of each of which has been limited of the two or more screens bridged by the interpolation blocks set in the interpolation block setting.