Why are the .zip files of compressed .jpegs about the same size?

Question

I am a new user of Linux OS's and I am trying Ubuntu 12.10 right in this days. The overall impression is quite positive, but there are some features that make it still complicated for use from most would-be users and in certain specific situations.

So, today I had to compress a couple of important .jpeg images into .zip files, to send them through Thunderbird to a Windows-using bureau (at least as I guess), and the outcome of the compression (simple way: right click-> compress-> .zip and same folder without password) were files of the very same size! :-(

I tried removing the .jpeg extension, I tried with formats other than .zip (although not sure they would be successfully opened from the recipient), I downloaded the "7zip" utility, I spent a while over all of this trying random things...not a different outcome than same-size files.

So, should I not be willing to use the command lines, how can I quickly compress these files or folders into .zip (not interested in other extensions at the moment) in case the simple procedure above does not work?

Sorry that you may find it a banal question, but I think these are the little hassles that prevent Unix-like OS's from becoming really widespread. Thank you for your help!

Answer 1

If the files were exactly the same size then something strange is going on. However, JPEG files will not compress much, if at all, with any typical archive software. It is expected that a 100kB JPEG file will be 99kB or larger when zipped.

Answer 2

Last step in JPEG compression is entropy coding, which is in essence very similar to what ZIP algorithm do:

• identify sub-strings that are more common and;
• give them shorter coded sequences;
• less common sub-strings will be mapped to longer sequences.

The length to use is computed based on how likely it is to see the substring in the complete file. The result is that in the coded file (JPEG or .ZIP), all substrings of size s now have roughly equivalent chance of occuring. As a result, both .ZIP and JPEG files will compress very poorly through an additional pass of entropy coding.

Answer 3

Lossy images (like jpeg-files) are hardly compressable. To further reduce the size of the zip-file, you must actually reduce screen size or quality of the images. This has nothing to do with which platform you use to zip files, you'll get the same results on a Windows machine.

If you do ever want to use the command line for this, you can as well have the zip-file created more efficiently (in terms of CPU cycles) with zip -0 zipfile.zip files. Your images will be stored and extracted without even trying to compress it.

Answer 4

well the zip compression is not that it compress so much may be few KB's and you will feel the difference if you compressed a very big file its not the problem of LINUX/UBUNTU that zip files have almost the same size its the zip protocol/encryption

as i compressed a .jpg file of size 33.7 KB the compressed file .zip of same file has 32 KB

yes, it has compressed but a very little

As you are not intresed in other extensions than follow these steps

1. Make a folder.

2. Copy all files in that folder

3. Right click

4. compress

5. click other options if you want to password protected zip

6. click compress

it will compress your all files and you will see the the size of un compressed folder and compressed folder is different

Answer 5

Indeed, zipping jpgs won't really work.
However, you can change the resolution.
Try using Phatch PHoto bATCH Processor (by example), it's in the Ubuntu Software Center.
You can do plenty stuff with it but what should interest you is the FIT option.
Divide by X the resolution of your images.
Best,

Answer 6

you can try using different compression methods such as tar along with gzip compression. Open the terminal and navigate to the folder containing your JPEG images. like tar -czvf your_archive_name.tar.gz your_folder_or_file_name.jpeg . On the other hand, Jpeg Compressor compress images and allow to download images in zip.