A method of processing image data comprising: receiving 2D image data representing a pixellated image with width and height; receiving a depth map in respect of the 2D image data; processing the depth map to derive a modified depth map; 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 one or both of: analysing luminance information in respect of the set of pixels, and modifying the depth map using a function which correlates depth with pixel height in the pixellated image and which has a different correlation between depth and pixel height for different luminance values, wherein the function implements: a first relationship between luminance and depth, such that high luminance values and low luminance values are assumed to be near to the viewer, a second relationship which is such that for high luminance values the function has a greater correlation between depth and pixel height than for low luminance values; analysing chrominance information in respect of the set of pixels, and modifying the depth map using a function which: for blue pixels, correlates depth with pixel height in the pixellated image and for the rest of the depth map depth is set to the previous depth map value. receiving 2D image data representing a pixellated image with width and height; receiving a depth map in respect of the 2D image data; processing the depth map to derive a modified depth map; 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 one or both of: analysing luminance information in respect of the set of pixels, and modifying the depth map using a function which correlates depth with pixel height in the pixellated image and which has a different correlation between depth and pixel height for different luminance values, wherein the function implements: a first relationship between luminance and depth, such that high luminance values and low luminance values are assumed to be near to the viewer, a second relationship which is such that for high luminance values the function has a greater correlation between depth and pixel height than for low luminance values; analysing chrominance information in respect of the set of pixels, and modifying the depth map using a function which: for blue pixels, correlates depth with pixel height in the pixellated image and for the rest of the depth map depth is set to the previous depth map value. receiving a depth map in respect of the 2D image data; processing the depth map to derive a modified depth map; 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 one or both of: analysing luminance information in respect of the set of pixels, and modifying the depth map using a function which correlates depth with pixel height in the pixellated image and which has a different correlation between depth and pixel height for different luminance values, wherein the function implements: a first relationship between luminance and depth, such that high luminance values and low luminance values are assumed to be near to the viewer, a second relationship which is such that for high luminance values the function has a greater correlation between depth and pixel height than for low luminance values; analysing chrominance information in respect of the set of pixels, and modifying the depth map using a function which: for blue pixels, correlates depth with pixel height in the pixellated image and for the rest of the depth map depth is set to the previous depth map value. analysing luminance information in respect of the set of pixels, and modifying the depth map using a function which correlates depth with pixel height in the pixellated image and which has a different correlation between depth and pixel height for different luminance values, wherein the function implements: a first relationship between luminance and depth, such that high luminance values and low luminance values are assumed to be near to the viewer, a second relationship which is such that for high luminance values the function has a greater correlation between depth and pixel height than for low luminance values; analysing chrominance information in respect of the set of pixels, and modifying the depth map using a function which: for blue pixels, correlates depth with pixel height in the pixellated image and for the rest of the depth map depth is set to the previous depth map value. a first relationship between luminance and depth, such that high luminance values and low luminance values are assumed to be near to the viewer, a second relationship which is such that for high luminance values the function has a greater correlation between depth and pixel height than for low luminance values; analysing chrominance information in respect of the set of pixels, and modifying the depth map using a function which: for blue pixels, correlates depth with pixel height in the pixellated image and for the rest of the depth map depth is set to the previous depth map value. for blue pixels, correlates depth with pixel height in the pixellated image and for the rest of the depth map depth is set to the previous depth map value.