Unraveling the JPEG

When you open a JPEG image on your computer, something (the browser, your operating system, or something else) has to decode the bytes to recover the original image as a list of colors that can then be displayed. By opening an image in a text editor, you’ve confused the computer, in the same way you confuse your brain when you rub your eyes too hard and start to see blotches of dimness and color! It’s almost a simple list of colors, where each byte changes exactly one pixel, and yet it’s already almost twice as small as the uncompressed image (which would be around 300 kb for this smaller size).

Source: parametric.press