Representing an image
A digital image file (typically associated with the extension “JPEG” or “PNG”) is comprised of an array of pixels. A pixel is the smallest constituting element of an image. In a grayscale image, each pixel is a scalar (single) value between 0 and 255: 0 is black, 255 is white, and anything in between is gray (the smaller the pixel value, the darker the pixel is). On the other hand, the pixels in color images are three-dimensional vectors that correspond to the scalar values that can be found in their red, green, and blue channels.
An image has height x width x c pixels, where height is the number of rows of pixels, width is the number of columns of pixels, and c is the number of channels. c is 3 for color images (one channel each for the red, green, and blue intensities of the image) and 1 for grayscale images. An example grayscale image containing 3 x 3 pixels and their corresponding scalar values is shown here:
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