Image processing method and image processing apparatus, program and recording medium, and image forming apparatus

An image processing apparatus comprising:

• a parameter calculating section for calculating a predetermined parameter representing whether an effective density pixel having a predetermined density value exists in an objective image which is a block image consisting of a plurality of pixels;
• an image converting section for performing image conversing processing for converting the objective image to an update image on lines from which one line is reduced in the detecting direction, when one of pixels in the objective image is defined as an interest pixel and a pixel neighboring downstream side in a predetermined first direction with respect to the interest pixel is defined as a neighboring pixel, by defining the interest pixel as the effective density pixel when a first condition on which the interest pixel is an effective density pixel and a second condition on which at least one neighboring pixel with respect to the interest pixel is an effective density pixel are satisfied, and by defining the interest pixel as an ineffective density pixel when either the first condition or the second condition is satisfied, as to each interest pixel having at least one neighboring pixel in the objective image, and for repeating the image converting processing until an objective image is lined on one line in the detecting direction after the update image is defined as the objective image again whenever the image converting processing is terminated;
• and
• a continuous-pixel-number calculating section for calculating the number of continuous pixels which represents the number of effective density pixel being spatially continuing in the block image on the basis of the parameter calculated by the parameter calculating section.