I have seen some websites split their images onto many smaller images, and tile them so they look like one image. What is the point of this, does it reduce page load time? If so what is the optimum size for the images to be split into? Does it help with .PNGs or just JPEGs? Thanks.
But since there's more images surely the total download size will be the same, so why does it reduce page load time? Also won't there have to be more code to put multiple images?
Slicing the bigger image into the smaller tiles will not help your page load time unless you make it with the image format limitations, your image contents, etc. in mind. For example if you have a photo with a large clickable rectangle button (1/3 height) with just a solid background and plain text, it would be a good idea to split such an image in two: JPG with the photo part and GIF with the button (because of the limited color palette). There are also more reasons behind slicing the images - repeatable pattern creation, applying a link, hover effect, etc. And regarding the image format - I usually use PNGs and JPGs, depending on the image type. I don't use GIF images, because they have less effective compression algorithm than PNGs.
If anything lots of smaller images will have a larger file size because every file has a minium file size that has info other than the image data. say this was 500byes. I big images that is 10.5kb - 500 bytes of this is other than image data. 10 smaller images 1kb each + 500 bytes to each for other data Results in a larger file size overall. This is just a guess. I'm not sure.
Are you referring to "Image mapping"? The intention of an image map is to provide an easy way of linking various parts of an image without dividing the image into separate image files.