Image processing method and apparatus

An image processing apparatus comprising:

• first error diffusion processing means comprising selective quantization means for quantizing input image data for each pixel to convert the quantized input image data into image data having a predetermined quantization level for outputting, when the gradation value of the input image data is within a predetermined quantization-executable range, and for outputting the input image data without quantizing the input image data, when the gradation value of the input image data is not within the predetermined quantization-executable range, and first error diffusion means for diffusing a quantization error of a target pixel produced through quantization in the selective quantization means to input image data of an unquantized pixel near the target pixel;
• and
• a second error diffusion processing means comprising quantization means for quantizing the image data outputted by the first error diffusion processing means for each pixel to convert the quantized image data into output image data having one of three or more quantization levels including a quantization level different from the quantization level at the selective quantization means for outputting, and second error diffusion means for diffusing a quantization error of the target pixel produced through quantization in the quantization means to image data of an unquantized pixel near the target pixel.