Why do image and video quality worsen the more they are saved and uploaded? What contributes to this?


Why do image and video quality worsen the more they are saved and uploaded? What contributes to this?

In: Technology

Every time you put content into editing software and make any changes, the saved file will be re-compressed and that will reduce the quality. RAW photo files, RAW format video, and so on do not suffer degrading if that is your saved format. The problem is that the file sizes for those are huge, so no one shares RAW format.

Many of the common file formats use various forms of ‘lossy’ compression, which means that they reduce the file size by discarding some of the information contained in the image/video. So each time you save the file again it gets compressed again, and more data is lost. The algorithms that they use are designed to keep the data that’s most important to the image quality, but they’re not perfect, so over multiple save/compression cycles, more and more of the original image is lost and the amount of weird compression artifacts grows.

There are ‘lossless’ compression file types/algorithms, but they generally don’t reduce file sizes nearly as much.

Websites have limited space. To save space, they compress your images and videos (so they take up less space).

In the process, some of the detail gets lost (because when you compress things, you lose data). Hence, the quality of the image/video gets worse.

The more you upload, the more this process repeats and the worse it all looks.

Saving and uploading files doesn’t affect quality. Our computers would be useless if we couldn’t reliably transfer exact copies of data. What causes quality to drop is when you’re 1) using a lossy compression algorithm such as JPEG or MPEG, and 2) repeatedly re-compressing the same file.

If you open a JPEG in an image editor like MS Paint, it has to decompress the image to show you the pixels. When you save, it needs to re-compress the file. Do this multiple times and it will lose quality each time.

Upload the image to an online service, and the site itself may also re-compress the image. Sometimes they do this so their images are in a consistent file format or resolution, or are below a certain file size.