As we saw in Chapter 2, Working with Camera Frames, OpenCV stores image data in a matrix of type Mat, which is like a multidimensional array. The rows and columns (specified by the first and second indices, respectively) correspond to the y and x pixel coordinates in the image. The elements are pixel values. A pixel value may be represented by one number (in the case of a grayscale image) or multiple numbers (in the case of a color image). Each of these numbers is said to belong to a channel. An opaque, grayscale image has just one channel, value (brightness), which is abbreviated as V. A color image may have as many as four channels—for example, red, green, blue, and alpha (transparency), which constitute the RGBA color model. Other useful models for color images include RGB (red, green, blue), HSV (hue, saturation, value), and YUV (brightness, greenness versus blueness, greenness versus redness). In this book, we focus on RGB and RGBA images, but OpenCV supports...