A device for adjusting the exposure of an image sensor includes an average luminance value calculation unit, a first exposure control unit and a correction exposure value calculation unit. The compressed fluid reservoir pressure may be decreased when the compressed fluid reservoir pressure is greater than a preset difference from the patient treatment pressure, particularly by venting the compressed fluid reservoir to atmosphere. The method comprises: selecting multiple preset keys from the matrix; detecting ghost keys among the matrix based on the selected preset keys; selecting multiple examining keys from the preset keys and the detected ghost keys, based on that at least one ghost key is included in the examining keys; and determining hidden ghost keys based on the examining keys. Such a material can be a material that is relatively rigid at relatively low temperature and low humidity outside the body and becomes soft on insertion into the body under the influence of temperature and moisture. Embodiments may produce compressed 2D images for which no specific light-field image viewer is needed to preview the full light-field image. Bursts of image information occupy a portion of each field time.