An image processing apparatus converts multi-valued data into multi-valued quantized data having fewer levels than the multi-valued data. The apparatus includes an acquisition unit that acquires threshold values, a provisional quantization unit that sets a provisional quantized value with respect to the multi-valued data, and a quantization unit that decides a quantized value with respect to the multi-valued data based on a result of comparing comparative multi-valued data for the multi-valued data to the threshold value. The quantization unit decides the quantized value so that in a case where the multi-valued data is the same intermediate value, pixels having the value larger than provisional quantized value increase, pixels having the provisional quantized value do not change in number, and pixels having the value smaller than the provisional quantized value decrease in a designated pixel area as the value of the multi-valued data rises.