1. A method of processing image data comprising: receiving 2D image data representing a pixelated image with a width and a height; receiving a depth map in respect of the 2D image data; processing the depth map to derive a modified depth map; and generating left and right image data together forming a 3D image based on the modified depth map and the 2D image data, wherein processing the depth map comprises at least one of: analyzing luminance information in respect of a set of pixels, and modifying the depth map using a midtone analysis of the luminance information of the image and a function which correlates depth with pixel height in the pixelated image and which has a different correlation between depth and pixel height for different luminance values, wherein the midtone analysis includes obtaining a ratio of a number of pixels with luminance within a central luminance band compared to a total number of pixels; and analyzing chrominance information in respect of the set of pixels, and modifying the depth map using a function which correlates depth with pixel height in the pixelated image and which has a different correlation between depth and pixel height for different chrominance values.