Patent ID: 8169663

Claim:
An image processing apparatus for scanning each pixel of an input image data in a raster order so as to quantize a multi-valued input pixel signal of said each pixel by using an error diffusion method, the image processing apparatus comprising: an error adding section for calculating an additional value by adding an input pixel value of a quantization-target pixel to a diffusion error diffused from a quantized pixel; a quantizing section for calculating an output pixel value of the quantization-target pixel by quantizing the quantization-target pixel based on a result of comparison between the additional value and a threshold value; an error calculating section for calculating a quantization error based on the input pixel value, the additional value, and the output pixel value obtained by the quantization of the quantization-target pixel; a diffusion error calculating section for calculating a diffusion error to be diffused to a non-quantized pixel based on the quantization error and a positional relation between the quantization-target pixel and the non-quantized pixel; an adjustment standard value generating section for setting an adjustment standard value for every quantization-target pixel according to the output pixel value of the quantization-target pixel, the adjustment standard value providing a standard of correction of the additional value or the threshold value at a time of quantization of the non-quantized pixel; an adjustment value calculating section for calculating an adjustment value to be used in quantizing the quantization-target pixel, the adjustment value calculating section calculating the adjustment value by attenuating, according to a distance between the quantized pixel and the quantization-target pixel, the adjustment standard value set for the quantized pixel; and a threshold value correcting section for correcting, based on the adjustment value, the threshold value or the additional value used in quantizing the quantization-target pixel.