>>5818430That's compression doing it's job.
Rather than saving every pixel, it saves data for every pixel to be recreated with some processing.
To put it simply, none of that data is actually "there". Rather than storing each pixel, the file stores "1000 lines, 1080 pixels wide, at the top, with this color. Fill it in" and the computer reads it and does as told when you go to view it. Once decoded, it does take up the actual size of a bitmap in your RAM. Once decoded it behaves the same as an uncompressed bitmap.
It seems like a win-win situation in every way, but it's actually not.
You ARE giving something up in return for this greatness, and that is CPU power.
For the use of viewing images, it's almost unnoticeable. If you wanted to save a movie as a PNG sequence, the decode time would stack up fast and cause editing/rendering/playback to be slower than normal at about 10 FPS assuming ~100ms decode time per frame.
Here is a good example of an image that doesn't compress well with Lossless compression.
It's more than half of the size of it as an uncompressed bitmap.
JPEG can take it down to less than 10%, but it degrades quality to do so.
JPEG doesn't even always win. Here is an example of where it's worse at file-size and quality.
PNG
http://i.imgur.com/Bmj0duX.pnghttp://i.imgur.com/lZ3MXHo.jpg>Introduces artifacts>Takes up more space 