A system for processing a three-dimensional image signal, the 3D image signal comprising a two-dimensional image signal and a 2D auxiliary signal, the 2D auxiliary signal being a 2D depth-related signal for enabling 3D rendering of the 2D image signal on a 3D display, the system comprising: - a signal input for obtaining the 2D image signal and the 2D auxiliary signal; - a user interface subsystem for enabling a user to establish a user-defined 2D region in the 2D image signal, the user-defined 2D region comprising an overlay; - a region definer for, based on the user-defined 2D region, defining a 2D auxiliary region in the 2D auxiliary signal, the 2D auxiliary region corresponding to a display region on a display plane of the 3D display when 3D rendering the 2D image signal using the 2D auxiliary signal; and - a depth processor for: i) obtaining a depth reduction parameter, the depth reduction parameter representing a desired amount of depth reduction in the display region towards a neutral display depth when 3D rendering the 2D image signal on the 3D display, and ii) deriving a gain value from the depth reduction parameter for enabling establishing the depth reduction in the display region towards the neutral display depth by iii) subtracting an offset corresponding to the neutral display depth from signal values of the 2D auxiliary signal within the 2D auxiliary region, applying the gain value as a multiplication factor, and re-adding the offset. - a signal input for obtaining the 2D image signal and the 2D auxiliary signal; - a user interface subsystem for enabling a user to establish a user-defined 2D region in the 2D image signal, the user-defined 2D region comprising an overlay; - a region definer for, based on the user-defined 2D region, defining a 2D auxiliary region in the 2D auxiliary signal, the 2D auxiliary region corresponding to a display region on a display plane of the 3D display when 3D rendering the 2D image signal using the 2D auxiliary signal; and - a depth processor for: i) obtaining a depth reduction parameter, the depth reduction parameter representing a desired amount of depth reduction in the display region towards a neutral display depth when 3D rendering the 2D image signal on the 3D display, and ii) deriving a gain value from the depth reduction parameter for enabling establishing the depth reduction in the display region towards the neutral display depth by iii) subtracting an offset corresponding to the neutral display depth from signal values of the 2D auxiliary signal within the 2D auxiliary region, applying the gain value as a multiplication factor, and re-adding the offset. i) obtaining a depth reduction parameter, the depth reduction parameter representing a desired amount of depth reduction in the display region towards a neutral display depth when 3D rendering the 2D image signal on the 3D display, and ii) deriving a gain value from the depth reduction parameter for enabling establishing the depth reduction in the display region towards the neutral display depth by iii) subtracting an offset corresponding to the neutral display depth from signal values of the 2D auxiliary signal within the 2D auxiliary region, applying the gain value as a multiplication factor, and re-adding the offset.