A method and apparatus for cooling a hat source configured along a lane. The base layer defines an aperture extending through the base layer and from the first surface to the second surface. A processing unit estimates the average value to be a level of a background image occupying a large area of a screen, and generates a signal indicating a minimum value at the average value and a maximum value at the maximum or minimum value as a compensated object signal. The image extraction unit produces processed image data by extracting pixels having pixel values contained in the extraction ranges from the input image data, and supplies the processed image data thus produced to the image detecting unit.