Image forming apparatus, image forming method, image density measuring apparatus, and image density measuring method

An image forming apparatus comprising:

• an image forming section which forms an image on paper by mixing n color materials, the n being a positive integer, and which forms, on paper, a gradation pattern image including color patches each of which includes gradation patches, wherein the color patches have colors different from each other, the colors ranging from a first color constituted of one color material among the n color materials to an nth color constituted of the n color materials, and the gradation patches have gradations different from each other;
• a reflectance detection section which detects a reflectance of each of the gradation patches of each of the color patches included in the gradation pattern image formed on the paper, and outputs reflectance information on the detected reflectance;
• and
• a control section which creates a gamma curve for each of the colors ranging from the first color to the nth color based on the reflectance information on each of the gradation patches of each of the color patches, the reflectance information being outputted from the reflectance detection section, to correct a gradation of input image data in such a way as to obtain a predetermined reflectance, wherein
• the control section (i) extracts a color composition of each of the colors ranging from the first color to the nth color from the input image data, (ii) on the color composition of an mth color, the m being 1 to n−1, performs a first gamma correction which corrects the gradation of the color composition of the mth color based on the gamma curve for the mth color so as to obtain a first corrected gradation value, and a second gamma correction which corrects the gradation of the color composition of the mth color based on the gamma curve for an (m+1)th color so as to obtain a second corrected gradation value, and interpolates the first corrected gradation value and the second corrected gradation value so as to determine an output value for the color composition of the mth color, (iii) on the color composition of the nth color, corrects the gradation of the color composition of the nth color based on the gamma curve for the nth color so as to obtain an output value for the color composition of the nth color, and (iv) combines the output values of the colors ranging from the first color to the nth color so as to generate output image data, and the image forming section forms an image on paper based on the output image data generated by the control section.