1. An image processing apparatus, comprising: an extraction unit configured to extract a low-frequency band component and a high-frequency band component from a radiation image formed by passing through a subject; a contrast enhancement processing unit configured to perform a contrast enhancement process to the extracted low-frequency band component; a detail enhancement processing unit configured to perform a detail enhancement process to the extracted high-frequency band component; a synthesis unit configured to synthesize an image resulting from performing the contrast enhancement process and an image resulting from performing the detail enhancement process; and a generation unit configured to reconstruct the synthesized image and generate a diagnosis image.