[Edit: Removed redundant commentary about headline.]
In: Mathematics
Human vision is actually a lot worse than we think. Video compression gets rid of details in the video that we aren’t likely to notice, and is able to shrink down the file size enormously that way.
For instance, we are much better at seeing the colors red and green than we are at seeing blue. If you watch just the blue color data from a compressed movie, you will find it is very blurry and low resolution, while the green and red data is more detailed.
Another example is that humans are much better at seeing light vs. dark rather than different shades of color. Compressed video retains a lot of information on the light/dark in the picture, while it minimizes the amount of color information stored.
Lastly, you can use tricks like only storing data of parts of the image that change. If the background remains the same, you only have to store that data once. This only works for scenes with small amounts of motion. If you watch heavily compressed videos, you will see that still scenes of people talking are often much more detailed than blurry action scenes where the whole screen is in motion.
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