1. An image processing apparatus configured to perform image processing on an image including image data with a negative value, the image processing apparatus comprising: a transformation unit configured to perform a nonlinear transformation processing on the image including image data with a negative value to transform the image including image data with a negative value into an image that does not include image data with a negative value; an image processing unit configured to perform predetermined image processing on the image that does not include image data with a negative value; and an inverse transformation unit configured to perform an inverse transformation processing of the nonlinear transformation processing on the image, having been subjected to the image processing, which does not include image data with a negative value to inversely transform the image, having been subjected to the image processing, which does not include image data with a negative value into an image, having been subjected to the image processing, which includes image data with a negative value.