Image processing method, image processing apparatus and storage medium

An image processing method comprising the steps of:

• reading an original and generating input image data;
• calculating the sharpness of said input image from said input image data;
• discriminating whether the original is a text original or a photograph original from the sharpness of said input image;
• and
• applying, in case said original kind discrimination step discriminates that said original is a text original, a density correction process to the input image obtained by reading said original;
• wherein said text image density correction step includes:
• a density histogram generation step of generating a density histogram from said input image;
• a density correction curve generation step of generating a density correction curve based on a ratio of the number of data close to the light and dark ends in said histogram to the total number of data in said histogram;
• and
• a density correction step of executing density correction on said input image, based on the density correction curve generated in said density correction curve generation step.

A storage medium which stores a computer readable program for realizing an image processing method, the method comprising the steps of:

• reading an original and generating input image data;
• calculating the sharpness of said input image from said input image data;
• discriminating whether the original is a text original or a photograph original from the sharpness of said input image;
• and
• applying, in case said original kind discrimination step discriminates that said original is a text original, a density correction process to the input image obtained by reading said original;
• wherein said text image density correction step includes:
• a density histogram generation step of generating a density histogram from said input image;
• a density correction curve generation step of generating a density correction curve based on a ratio of the number of data close to the light and dark ends in said histogram to the total number of data in said histogram;
• and
• a density correction step of executing density correction on said input image, based on the density correction curve generated in said density correction curve generation step.

An image processing apparatus comprising:

• an image reading circuit, arranged to read an original and generating input image data;
• an original kind discriminating circuit, arranged to discriminate whether said original is a text original or a photograph original from the sharpness of said input image;
• a text image density correction curve generating circuit, arranged to generate, in case said original kind discrimination circuit discriminates that said original is a text original, a text image density correction curve for applying a density correction process to the input image;
• and
• a text image density correction circuit, arranged to execute a density correction process of the input image obtained by reading said original, utilizing said text image density correction curve;
• wherein said text image density correction curve generating circuit includes:
• a density histogram generation circuit, arranged to generate a density histogram from said input image;
• a density correction curve generation circuit, arranged to generate a density correction curve based on a ratio of the number of data close to the light and dark ends in said histogram to the total number of data in said histogram;
• and
• a density correction circuit, arranged to execute density correction on said input image, based on the density correction curve generated in said density correction curve generation circuit.

An image processing method comprising the steps of:

• reading an original with a first reading condition to generate input image data;
• calculating the sharpness of said input image from said input image;
• discriminating whether the kind of the original is a text original or a photograph original, based on the sharpness of said input image;
• and
• applying, in case said original kind discrimination step discriminates that said original is a photograph original, a density correction process to the input image obtained by reading said original;
• wherein said photograph image density correction step includes:
• a density histogram generation step of generating a density histogram from said input image;
• a cumulative histogram generation step of cumulating the frequency of density level values in an increasing direction of the density level value, taking the minimum density level value of data of the density histogram obtained in said density histogram generation step as a reference and starting point of cumulating operation, thereby obtaining a cumulative histogram indicating the relationship between the density level value and the cumulated value;
• a first γ value obtaining step of calculating an approximation exponential function approximating said cumulative histogram and obtaining a first γ value indicating the density correction coefficient of the input image from the exponent of thus calculated function;
• and
• a first density correction step of executing a density correction process of said input image, based on said first γ value.

A storage medium which stores a computer readable program for realizing an image processing method, the method comprising the steps of:

• reading an original to generate input image data;
• calculating the sharpness of said input image from said input image;
• discriminating whether the kind of the original is a text original or a photograph original, based on the sharpness of said input image;
• and
• applying, in case said original kind discrimination step discriminates that said original is a photograph original, a density correction process to the input image obtained by reading said original;
• wherein said photograph image density correction step includes:
• a density histogram generation step of generating a density histogram from said input image;
• a cumulative histogram generation step of cumulating the frequency of density level values in an increasing direction of the density level value, taking the minimum density level value of data of the density histogram obtained in said density histogram generation step as a reference and starting point of cumulating operation, thereby obtaining a cumulative histogram indicating the relationship between the density level value and the cumulated value;
• a γ value obtaining step of calculating an approximation exponential function approximating said density histogram and obtaining a γ value indicating the density cumulative correction coefficient of the input image from the exponent of thus calculated function;
• and
• a density correction step of executing a density correction process of said input image, based on said γ value.

An image processing apparatus comprising:

• an image reading apparatus, arranged to read an original to generate input image data;
• a sharpness calculation circuit, arranged to calculate the sharpness of said input image from said input image;
• an original kind discrimination circuit, arranged to discriminate whether the kind of the original is a text original or a photograph original, based on the sharpness of said input image;
• and
• a photograph image density correction circuit, arranged to apply, in case said original kind discrimination circuit discriminates that said original is a photograph original, a density correction process to the input image obtained by reading said original;
• wherein said photograph image density correction circuit includes:
• a density histogram generation circuit, arranged to generate a density histogram from said input image;
• a cumulative histogram generation circuit, arranged to cumulate the frequency of density level values in an increasing direction of the density level value, taking the minimum density level value of data of the density histogram obtained in said density histogram generation circuit as a reference and starting point of cumulating operation, thereby obtaining a cumulative histogram indicating the relationship between the density level value and the cumulated value;
• a γ value obtaining circuit, arranged to calculate an approximation exponential function approximating said cumulative histogram and obtaining a γ value indicating the density correction coefficient of the input image from the exponent of thus calculated function;
• and
• a density correction circuit, arranged to execute a density correction process of said input image, based on said γ value.