Posted by Stephen Kiernan, follow me on Twitter.

One thing that most people have to do quite a bit if they have a website with a lot of photographs on it is resizing. It’s great to keep high resolution, high Megabyte originals on your hard-drive, but when displaying them on a website, one must account for their monthly bandwidth allowance from whatever provider they are affiliated to. Even more importantly, they have to be aware that visitors will not hang around long waiting for large files to download. So it’s good idea to know that when it comes to minimizing megabytes, some programs out there are better at resizing an image than other. A lot better. You have a lot of flexibility when dealing with thumbnails also because in addition to them being low resolution, they don’t have to be saved at the highest quality either.

For this little comparison a RAW image (saved size is 18.3MB) with a resolution 3488×2616pixels was converted to a jpg in Photoshop without any other post-processing. The image quality was set to level 10 and saved, giving a new saved size of 2.3MB. I usually give thumbs of pictures an resolution of 400×300pixels so the visitor can still see the image clearly without having to wait long for it to load. In Photoshop, resizing this jpg down to 400×300pixels using the Bicubic Sharper algorithm and saving it at level 4 (low). The resulting file still comes out at 116kb! Far too big for a thumbnail image I think! The image can be seen here.

Using the exact same procedure in GIMP the image came out at 20kb, which is much more manageable. The GIMP output can be seen here. Some of the vibrancy in colour has been lost in the GIMP version but I would argue that this loss in detail is more than compensated for by the 500%+ reduction in file-size. Remember, thumbnails are only supposed to be links to larger, better quality images, they only serve to give the visitor a sneak preview of the full picture. Bear in mind that this was merely a rough and ready comparison between the two programs; no doubt there are numerous settings I could have toyed with for hours to give a different result - I simply went with the default settings for now as they both give reasonable results and you shouldn’t dwell too much on thumbnail quality anyway.