Why do PDFs not compress well?

In general, PDFs contain images and such that are already compressed, so it will not compress much further. Your algorithm is probably only able to eke out meagre if any savings based on the text strings contained in the PDF?

Why do some files look larger when compressed?

You say the folder was mostly pictures and movies. Usually those are already in compressed format and won’t compress any farther. In fact a zipped file of an already compressed file can end up being larger than the original because there is a certain amount of overhead in creating a zipped version.

What file types do not compress?

TIFF or Tagged Image File Format are lossless images files meaning that they do not need to compress or lose any image quality or information (although there are options for compression), allowing for very high-quality images but also larger file sizes.

How do I resize a PDF without losing quality?

To do so,

1. Open your PDF file in Preview. It should be the default option, but in case it isn’t, Right Click on the PDF file, select Open with > Preview.
2. Then, click File > Export, and in the Quartz Filter drop-down box, select Reduce File Size.
3. The software will automatically reduce the size of the PDF file.

Why are compressed files smaller?

Lossy compression reduces file size by removing unnecessary bits of information. This type of compression is most commonly used on image, video, and audio files, where a perfect representation of the source media is not required.

Can all files be compressed?

It is a quite common experience that not all file types can be compressed with equal efficiency: some data structures, like text files, or text based containers (spreadsheets, documents, databases) usually compresses well, reaching high compression ratio, while other formats, usually multimedia files, does not compress …

Why do some files not compress?

Again, if you create Zip files and see files that cannot be significantly compressed, it is probably because they already contain compressed data or they are encrypted. If you would like to share a file or some files that do not compress well, you might: Email photos by zipping and resizing them.