Zip files don't become smaller

I believe I understand your problem, but let's figure out what you have. What image format are the large files? What is a typical file size in MB or GB?

I thought that one of the benefits of zipping files, was to make it easier to send them. The person at the other end can unzip them and have the full size original files.

That is true but the file must be capable of being compressed. Think of any file as a coil spring that is an inch long. There is space between the coils with the spring at rest. Compressing the spring reduces the space between the coils until eventually the coils touch each other--that is the maximum possible compression without deforming the steel.

Common compressions formats for images (jpg; png; bmp; gif) start by compressing the file. The "spaces between the coils," so to speak, are already mostly removed when you save the file in one of those formats.You may be able to zip them a little but, like a spring whose coils touch, there is a limit.

I routinely send images in PhotoShop format (.psd) to a magazine. I use the regular Mac compression thing and they get smaller because .psd is NOT a compression format. If I try the same thing with a jpg formatted image, it compresses little to none at all.

Allan

Many image files are already in compressed formats. You can't compress them farther. With jpegs you can open them in Preview and use the "Adjust Size...." command in the Tools menu to make the files smaller, then attach them.