The image data forming apparatus and an image data processing method for recording image data on an image data recording medium in a wide dynamic range and reproducing a finished image from the image data. The apparatus separates a wide dynamic range image signal of an image, generated from a solid-state imaging device, into main data M suitable for forming the finished image and highlight data H having a higher range with the use of a range separator, associates the main data M with the highlight data H, and records them in an image recording memory. At this time, a main data processor performs gradation control and compression on the main data M. A highlight data processor performs gradation control and compression on the highlight data H as necessary. An image reproducer reads out the main data M and the highlight data H, associated with each other as one image, from the image recording memory and develops them on a common axis Q for composition. This restores the original dynamic range image signal and allows the image to be reproduced on a printer. From the main data M, the image is displayed on a video monitor as the finished image.