This section of the site is for general concepts relating to signal and image processing. In cryo-ET, most of the data we work with are single channel (grayscale) images from transmission electron microscopes.
Digital images are arrays of point samples, each with an associated value. In 2D these point samples are known as pixels, in 3D they are called voxels.
If your mental model for a pixel is ‘a little square’, you may enjoy reading this technical memo from Alvy Ray Smith titled ‘A pixel is not a little square!’.