Research has been under way for many years on technology that reduces, using a plurality of temporally successive images such as moving images or a plurality still images taken in rapid succession, noise components contained in the values of pixels in any one of the plurality of images. Such technology is referred to as three-dimensional noise reduction (3DNR).
In one example of an image correction apparatus using 3DNR, any fluctuating component contained in each pixel value of the image along the time axis is the noise component to be removed. Therefore, the image correction apparatus reduces the noise component by taking a time average of the values of the pixels located at the same position in a plurality of temporally successive images. To achieve this, the image correction apparatus, for example, calculates the difference between the value of each pixel in the current image and the value of the corresponding pixel in the past image, multiplies the difference value by a feedback coefficient, and adds the product to the value of that pixel in the current image. However, the position of a motion region containing a moving object differs from one image to the next. As a result, if the pixel values taken from the same position in the plurality of images are averaged over time, since the values of the pixels contained in the moving object and the values of the pixels not contained in the moving object are averaged together in areas along their boundaries, an afterimage of the moving object occurs along the boundaries, resulting in a blurred image.
In view of the above, a technique that reduces the effects of the afterimage by reducing the feedback coefficient k if the difference value between the current video signal and the video signal one frame back is large, and that reduces noise by increasing the feedback coefficient k if the difference value is small is proposed (for example, refer to Japanese Laid-open Patent Publication No. 2000-209507). Further, a technique that obtains the filter coefficient k of a low-pass filter to be applied between the current frame and the motion-compensated previous frame, from both the absolute value of the interframe difference and the absolute value of the neighboring pixel difference within the frame is proposed (for example, refer to Japanese Laid-open Patent Publication No. H07-288719).
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