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We first extract the contours of the black keys, which are relatively easy compared to detecting the white keys. As the black keys cause interference in detecting white keys, we first process the black keys and truncate the detected area.
We use Gaussian blur to remove the details and noises that interfere with the contour detection and also perform Otsu's thresholding for preparing for contour extraction. We further perform the Convex Hull Algorithm in order to add outlines to the image. (Otherwise, the detection won't work because the black keys blend with the black background.) After detecting the black keys' contours using OpenCV's function, we truncate the black key area to reduce the unnecessary noise and binarize the image again with the Adaptive Thresholding Algorithm to finally detect the white keys' contours.
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IEEE/ICACT20250052 Slide.07
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