When it comes to uploading images to a website you always want to try and make sure the file sizes are as low as possible without compromising on quality. Sometimes that is easier said than done, but with the free ImageOptim for the Mac it’s a breeze.
ImageOptim can handle a variety of different image formats including PNG, JPG, and GIF. In general the file size savings depends on the image and how much it is able to compress it, and if you jump into the preferences for ImageOptim you can configure the settings available for the images. By default it will set the quality of JPG images to 90%, and so you might start to see some minor artifacts in the images caused by the app if you don’t tweak the settings at all. You can configure it to retain the full quality of the images though, and only have it try to reduce the JPG sizes by removing things like EXIF data and comments found in them.
When it comes to PNG images, however, they can often be significantly optimized without any loss of quality. How does it do that? One example the website mentions is that it will convert images from being a 24-bit PNG to 8-bit PNG with full alpha channel, but it will only do so when it won’t affect the quality of the image. It also runs the PNG images through several other image optimization tools to get the size down as much as possible.
ImageOptim Homepage (Mac only; Freeware)