Area separating apparatus, image processing apparatus employing the same, and area separating method

An area separating apparatus for judging whether or not each object pixel belongs to a thin line image area in an image on the basis of image data indicative of density gradation levels of pixels constituting the image, the apparatus comprising:

• a first direction density difference summing circuit for determining differences in image data between respective adjacent pairs of pixels aligning in a first direction in a second image block of a predetermined size containing the object pixel and summing the image data differences for all the pixels in the second image block for determination of a first direction density difference sum;
• a second direction density difference summing circuit for determining differences in image data between respective adjacent pairs of pixels aligning in a second direction different from the first direction in the second image block and summing the image data differences for all the pixels in the second image block for determination of a second direction density difference sum;
• and
• a second judgment circuit for judging whether or not the object pixel belongs to the thin line image area on the basis of a magnitude relationship between the first direction density difference sum and the second direction density difference sum respectively calculated by the first direction density difference summing circuit and the second direction density difference summing circuit.

An image processing apparatus for processing image data indicative of density gradation levels of pixels constituting an image in accordance with a judgment on whether or not each object pixel belongs to a photograph image area in the image, the apparatus comprising:

• an average value calculating circuit for calculating an average value of image data of pixels in a first image block of a predetermined size containing the object pixel;
• a photograph image area judgment threshold generating circuit for generating a photograph image area judgment threshold in accordance with the average value calculated by the average value calculating circuit;
• a density difference summing circuit for determining differences in image data between respective adjacent pairs of pixels in the image block and calculating a sum of the image data differences for all the pixels in the image block;
• a first judgment circuit which judges that the object pixel belongs to the photograph image area if the sum of the image data differences calculated by the density difference summing circuit is smaller than the photograph image area judgment threshold generated by the photograph image area judgment threshold generating circuit, and judges that the object pixel does not belong to the photograph image area if the sum of the image data differences is not smaller than the photograph image area judgment threshold;
• and
• a halftoning circuit for performing a dot concentration halftoning process on pixels judged to belong to the photograph image area and performing a dot distribution halftoning process on pixels judged not to belong to the photograph image area.

An area separating method for judging whether or not each object pixel belongs to a photograph image area in an image on the basis of image data indicative of density gradation levels of pixels constituting the image, the method comprising the steps of:

• calculating an average value of image data of pixels in a first image block of a predetermined size containing the object pixel;
• determining differences in image data between respective adjacent pairs of pixels in the image block and calculating a sum of the image data differences for all the pixels in the image block;
• and
• performing a first judgment process to judge that the object pixel belongs to the photograph image area if the sum of the image data differences is smaller than a photograph image area judgment threshold determined in accordance with the average value, and to judge that the object pixel does not belong to the photograph image area if the sum of the image data differences is not smaller than the photograph image area judgment threshold.

An area separating method for judging whether or not each object pixel belongs to a thin line image area in an image on the basis of image data indicative of density gradation levels of pixels constituting the image, the method comprising the steps of:

• determining differences in image data between respective adjacent pairs of pixels aligning in a first direction in a second image block of a predetermined size containing the object pixel and summing the image data differences for all the pixels in the second image block for determination of a first direction density difference sum;
• determining differences in image data between respective adjacent pairs of pixels aligning in a second direction different from the first direction in the second image block and summing the image data differences for all the pixels in the second image block for determination of a second direction density difference sum;
• and
• performing a second judgment process to judge whether or not the object pixel belongs to the thin line image area on the basis of a magnitude relationship between the first direction density difference sum and the second direction density difference sum.