An image processing apparatus for quantizing input image data having gradation of an m value, where m is a natural number, into output image data having gradation of an n value, where n is a natural number smaller than m, the image processing apparatus comprising: quantization means configured to quantize an input value having gradation of an m value in input image data into an output value having gradation of an n value in output image data; and plane separation means configured to determine an output value corresponding to a target pixel of eachof a plurality of planes, based on the quantization value of the target pixel quantized by the quantization means, wherein the plurality of planes includes at least two types of planes, characterized in that the plane separation means is configured, in the case that the quantization value of the target pixel represents ON of a dot, to set the quantization value representing ON of a dot to an output value corresponding to the target pixel of any one of the plurality of planes, based on the maximum of the sum of distance information of the target pixel of each plane and the weighted input/output error of each plane, the distance information of the target pixel indicating a distance from a pixel having a quantization value representing ON of a dot which has been previously set, wherein the planes of at least two types include at least one set of planes corresponding to a plurality of passes in a multipass recording method, planes corresponding to a plurality of recording materials, and planes corresponding to a plurality of discharge amounts of a recording material, and wherein, in the case that the quantization value of the target pixel represents ON of a dot, the plane separation means is configured to update the distance information for each plane. quantization means configured to quantize an input value having gradation of an m value in input image data into an output value having gradation of an n value in output image data; and plane separation means configured to determine an output value corresponding to a target pixel of eachof a plurality of planes, based on the quantization value of the target pixel quantized by the quantization means, wherein the plurality of planes includes at least two types of planes, characterized in that the plane separation means is configured, in the case that the quantization value of the target pixel represents ON of a dot, to set the quantization value representing ON of a dot to an output value corresponding to the target pixel of any one of the plurality of planes, based on the maximum of the sum of distance information of the target pixel of each plane and the weighted input/output error of each plane, the distance information of the target pixel indicating a distance from a pixel having a quantization value representing ON of a dot which has been previously set, wherein the planes of at least two types include at least one set of planes corresponding to a plurality of passes in a multipass recording method, planes corresponding to a plurality of recording materials, and planes corresponding to a plurality of discharge amounts of a recording material, and wherein, in the case that the quantization value of the target pixel represents ON of a dot, the plane separation means is configured to update the distance information for each plane.