Image processing apparatus and image processing method for formation of high quality image by high-speed error diffusion processing by execution of more complicated threshold condition processing in a simple manner. When error diffusion processing is performed on multivalued image data having plural density components and the result of processing is outputted, upon execution of error diffusion processing on a first density component among the plural density components, a threshold value used in the error diffusion processing is determined based on a density value of a second density component, then the error diffusion processing is performed on the first density component based on the determined threshold value, and the result of execution of the error diffusion processing is outputted. Further, upon execution of the error diffusion processing on the second density component among the plural density components, a threshold value used in the error diffusion processing is determined based on a density value of the first density component, then the error diffusion processing is performed on the second density component based on the determined threshold value, and the result of the error diffusion processing is outputted.