An image processing device includes a processor and a memory storing instructions causing the processor to: generate a first intermediate image by applying, to an input image, inverse conversion being inverse of conversion corresponding to degrading process of imaging the input image; generating a second intermediate image by adding a frequency component to the input image; generate a weighting factor so that a second residual error between a second image and the input image becomes smaller than a first residual error between a first image and the input image, the first image being obtained by applying the conversion to the second intermediate image, and the second image being obtained by applying the conversion to a composite image obtained by the weighted addition of the first and second intermediate images; and generate the composite image by performing the weighted addition of the first and second intermediate images using the weighting factor.