So, I'm working on a couple of different websites. They use a bunch of images, and ... they take some time to load those images. I can show an image loading animation and what have you, but I do want to reduce the loading time as much as possible. So, here's a thought. Let's say that one of websites uses 30 images. I combine some of them and make them into one big image so that fewer http requests will be made. Now, does this reduce the loading time? Also is this worth the effort?
It will increase the loading time rather then decrease, loading one big image is slower than simultaneously loading several small images. Another way why not reduce the resolution instead?
This is not necessarily true. If you can make a GIF file (limited to 256 colors) without degrading the quality of each individual image, then do that. If you can't reduce the colors, most of the time a PNG file can be used instead of a GIF. The fewer HTTP requests your visitors have to make, the better - even if the size of the large file is somewhat bigger than the sum of the individual file sizes (within reason, of course). Read Yahoo's document Best Practices for Speeding Up Your Web Site for more about this and other tricks.