Image processing apparatus and image processing method

An image processing apparatus, comprising:

• background color specifying means for specifying a background color of an original document using RGB signals of image data acquired by reading the original document;
• hue determination means for determining a hue of a pixel in the image data;
• and
• monochrome signal generation processing means for generating a monochrome signal using at least one of the RGB signals according to a specification result of the background color specifying means and a determination result of the hue determination means,
• wherein, in the hue determination means, if the hue is found to be a chromatic color, the hue is determined by comparing a hue signal with the conditional equations below:
• if hue signal≦thh1 or hue signal>thh6, then the hue is red;
• if thh1<hue signal≦thh2, then the hue is yellow;
• if thh2<hue signal≦thh3, then the hue is green;
• if thh3<hue signal≦thh4, then the hue is cyan;
• if thh4<hue signal≦thh5, then the hue is blue;
• and
• if thh5<hue signal≦thh6, then the hue is magenta, and
• wherein the background color specifying unit calculates total frequencies of hues including black, red, yellow, green, cyan, blue, magenta, and white and compares the total frequencies of the respective hues with a specific threshold value using the conditional equations below:
• if a total frequency of black>bg th1, then the black hue is the background;
• if a total frequency of black≦bg th1, then the black hue is not the background;
• if a total frequency of red>bg th2, then the red hue is the background;
• if a total frequency of red ≦bg th2, then the red hue is not the background;
• threshold determination is performed for each of yellow, green, cyan, blue, magenta, and white in the same manner.

An image processing method performed by a computer in an image processing apparatus, comprising the steps of:

• specifying a background color of an original document using RGB signals of image data acquired by reading the original document;
• determining a hue of a pixel in the image data;
• and
• generating a monochrome signal using at least one of the FGB signals according to a specification result in the step of specifying the background color and a determination result in the step of determining the hue,
• wherein, in the determining the hue, if the hue is found to be a chromatic color, the hue is determined by comparing a hue signal with the conditional equations below:
• if hue signal≦thh1 or hue signal>thh6, then the hue is red;
• if thh1<hue signal≦thh2, then the hue is yellow;
• if thh2<hue signal≦thh3, then the hue is green;
• if thh3<hue signal≦thh4, then the hue is cyan;
• if thh4<hue signal≦thh5, then the hue is blue;
• and
• if thh5<hue signal≦thh6, then the hue is magenta, and
• wherein, in the specifying the background color, total frequencies of hues including black, red, yellow, green, cyan, blue, magenta, and white are calculated and the total frequencies of the respective hues are compared with a specific threshold value using the conditional equations below
• if a total frequency of black>bg th1, then the black hue is the background;
• if a total frequency of black≦bg th1, then the black hue is not the background;
• if a total frequency of red>bg th2, then the red hue is the background;
• if a total frequency of red ≦bg th2, then the red hue is not the background;
• threshold determination is performed for each of yellow, green, cyan, blue, magenta, and white in the same manner.