Comparing colors

The next technique to detect motion is by comparing colors across different frames. Firstly, we identify a pixel in the video frame. We store the pixel color information in the Pure Data patch. In the subsequent frame, we compare the color of that pixel with the stored information. If the colors change significantly, we assume there is movement in that area. To work with these tasks, we have to know the pixel color information. The pix_data object does it. We have briefly introduced it in Chapter 3, Image Processing, in the image-processing examples. Now we make use of it for interaction design:

We need to provide four inlets for the pix_data object. The first one is a bang message to trigger the reading of the pixel color. The second is the video image. The last two are the X and Y positions of the pixel in the range between 0 and 1. We use two horizontal sliders for the X and Y positions. The position (0, 0) is the top-left corner. The position (1, 1) is the bottom-right...