A head mounted display system (200, 400) comprising: a frame configured to be supported on a head of a user; a display disposed on the frame, said display configured to project light associated with a virtual image into said user's eye to display virtual image content to the user and further configured to transmit light from an environment to the user's eye to provide a view of a portion of the environment to the user; a waveguide assembly associated with the display; a camera configured to obtain images of the environment at a frame rate, said camera having a field of view; and processing electronics configured to receive and process frames containing the images obtained by the camera, wherein said image processing comprises: assessing relative motion between said head mounted display and one or more features in said environment, said assessment of relative motion comprising determining whether the head mounted display has moved, is moving or is expected to move with respect to one or more features in the environment and/or determining whether one or more features in the environment have moved, are moving or are expected to move relative to the head mounted display; determining one or more virtual image content locations in the environment corresponding to a location where renderable virtual image content appears to a user when the location appears in the display; comparing said one or more virtual image content locations in the environment with a viewing zone that includes at least a portion of said field of view of said camera; and characterised in that said image processing further comprises: based on (i) said assessment of relative motion between said head mounted display and one or more features in said environment and (ii) on said comparison of said one or more virtual image content locations in the environment with the viewing zone, altering the frame rate of the camera from a first frame rate to a second frame rate and/or adjusting the amount of processing on the frames containing the images obtained by the camera that are processed by the processing electronics. a frame configured to be supported on a head of a user; a display disposed on the frame, said display configured to project light associated with a virtual image into said user's eye to display virtual image content to the user and further configured to transmit light from an environment to the user's eye to provide a view of a portion of the environment to the user; a waveguide assembly associated with the display; a camera configured to obtain images of the environment at a frame rate, said camera having a field of view; and processing electronics configured to receive and process frames containing the images obtained by the camera, wherein said image processing comprises: assessing relative motion between said head mounted display and one or more features in said environment, said assessment of relative motion comprising determining whether the head mounted display has moved, is moving or is expected to move with respect to one or more features in the environment and/or determining whether one or more features in the environment have moved, are moving or are expected to move relative to the head mounted display; determining one or more virtual image content locations in the environment corresponding to a location where renderable virtual image content appears to a user when the location appears in the display; comparing said one or more virtual image content locations in the environment with a viewing zone that includes at least a portion of said field assessing relative motion between said head mounted display and one or more features in said environment, said assessment of relative motion comprising determining whether the head mounted display has moved, is moving or is expected to move with respect to one or more features in the environment and/or determining whether one or more features in the environment have moved, are moving or are expected to move relative to the head mounted display; determining one or more virtual image content locations in the environment corresponding to a location where renderable virtual image content appears to a user when the location appears in the display; comparing said one or more virtual image content locations in the environment with a viewing zone that includes at least a portion of said field of view of said camera; and characterised in that said image processing further comprises: based on (i) said assessment of relative motion between said head mounted display and one or more features in said environment and (ii) on said comparison of said one or more virtual image content locations in the environment with the viewing zone, altering the frame rate of the camera from a first frame rate to a second frame rate and/or adjusting the amount of processing on the frames containing the images obtained by the camera that are processed by the processing electronics.