When I first started putting pictures on my web site I used to delete the originals (at the time I only had a 3.2G hard drive in my main machine and used CDs for backup so I didn’t feel inclined to waste too much space). The problem is that I optimised the images for viewing on displays of the day (when 1024×768 was high resolution and I tried to get pictures down to 800×600 or less whenever possible). Also the program I was using at the time for scaling the images didn’t do it nearly as well as the Gimp does now.
Now when putting pictures on my web site I keep the original JPEG’s in a safe place so that if there are future changes to common display technology, net connection speed (particularly the speed of my server) or of technology for scaling and compressing images then I can re-do them to get a better result.
When saving images with Gimp I enable “Advanced Options”, this allows me to set a floating-point DCT method this saves about 400 bytes on disk and apparently gives a better image quality too – it’s not noticably slow on a Pentium-M 1.7GHz so they should probably make it the default. The next “Advanced” option to change is to turn off “Save EXIF data” (saves 1.9K) and “Save thumbnail” (can save almost 5K depending on the image).
The next thing to do when saving a JPEG is to enable the “Show Preview in image window” setting. This allows you to adjust the image quality while seeing the resulting image as well as the size, so you can determine which combination of file size and image quality is best for you. This is much easier than saving
a file and then running an image viewing program to inspect it!
As an aside, it would be convenient if the Gimp would reposition it’s “Save as” dialogue to not occlude the image window and would enable the preview option by default on machines with reasonably fast CPUs.