When working with digital images, you always have a fixed number of original pixels to work with. The number is determined by the number of photosites on the image sensor. To make an image smaller, some of those pixels are removed. To make an image larger, new pixels have to be added. Images don't get better, they just get bigger.
Aspect ratios Image sensors have different aspect ratios-the ratio of image height to width.
Most image sensors fall in between these extremes. The aspect ratio of a sensor is important because it determines the shape and proportions of the photographs you create. When an image has a different aspect ratio that the device it's displayed or printed on, it has to be cropped or resized to fit. Your choice is to loose part of the image or waste part of the paper. To imagine this better, try fitting a square image on a rectangular piece of paper.