Adaptive Threshold for Infrared Subject Extraction

Example 1

In the subject region extraction processing (S15) of FIG. 3, the subject region extraction unit 15 may change (adjust) the predetermined threshold used for the background differentiation between the infrared image and the background infrared image in accordance with the intensity of the infrared light radiated from the infrared lamps 4. Specifically, the subject region extraction unit 15 also increases the threshold when the intensity of the infrared light is large. That is, the threshold is set to be larger in proportion to the intensity of the infrared light. For example, when the infrared lamps 4 are adjusted to increase the intensity of the infrared light and the pixel values of the background region of the infrared image double in brightness, the change in the pixel values in the subject region is also relatively doubled. As a result, the difference value between the pixel values of the infrared image and the background infrared image is also considered to be doubled. Therefore, by doubling the threshold, it is possible to keep the threshold appropriate for the extraction of the subject region.