Image processing apparatus and image processing method

1. An image processing apparatus, comprising:

an input section inputting information of an image;

a converter converting the information of the image inputted by said input section into information suitable for edge detection; and

an image processor calculating a difference value of each image unit between adjacent image units mutually in a predetermined direction to generate an edge image based on the converted information of the image,

wherein the image processor adds an absolute value of the difference value of the image unit to a difference value of adjacent image unit to the image unit in the predetermined direction when the difference value of the image unit calculated by the image processor is negative,

wherein the input section inputs information of an image in which an area of noninverted characters and an area of inverted characters are mixed, and

wherein the image processor generates an edge image for the noninverted characters and an edge image for the inverted characters, selects either of the generated edge images for each character string area, and composes the selected edge images for each character string area to form one edge image.

2. An image processing apparatus according to claim 1 ,

wherein said converter converts the inputted information of the image into density and color information, and

wherein said image processor generates edge images for each of the density and color information which are obtained by said converter, and composes these generated edge images to form one edge image.

3. An image processing apparatus according to claim 1 ,

wherein said image processor selects, out of the generated edge images, the edge image whose average value in size of character areas contained in the character string area is smaller, for each character string area.

4. An image processing apparatus according to claim 1 ,

wherein said image processor determines a character string area whose average value in size of character areas is equal to or higher than a threshold value in the generated edge image, generates a binarized image of an original image in this character string area, and composes this binarized image, instead of the edge image of the same character string area, with images of the other character string areas.

5. An image processing method, comprising:

converting inputted information of an image into information suitable for edge detection;

calculating a difference value of each image unit between adjacent image units mutually in a predetermined direction to generate an edge image based on the converted information of the image;

adding an absolute value of the difference value of the image unit to a difference value of adjacent image unit to the image unit in the predetermined direction when of the calculated difference value of the image unit is negative, to generate an edge image;

inputting information of an image in which an area of noninverted characters and an area of inverted characters are mixed;

generating from the inputted information of the image an edge image for the noninverted characters and an edge image for the inverted characters;

selecting either of the generated edge images for each character string area; and

composing the selected edge images for each character string area to form one edge image.

6. An image processing method according to claim 5 , further comprising:

converting the inputted information of the image into density and color information; and

generating edge images for each of the density and color information after the conversion, and composing these generated edge images to form one edge image.

7. An image processing method according to claim 5 , further comprising:

selecting, out of the generated edge images, the edge image whose average value in size of character areas contained in the character string area is smaller, for each character string area.

8. An image processing method according to claim 5 , further comprising:

determining a character string area whose average value in size of character areas is equal to or higher than a threshold value in the generated edge image, generating a binarized image of an original image in this character string area, and composing this binarized image, instead of the edge image of the same character string area, with images of the other character string areas.