I spent a few hours today (96-03-30) experimenting with picture sizes. It all started when I wanted a new Desktop picture because I had an extra 16 MB RAM and 1 GB drive, so that Memsize would look impressive!!!
When I converted the saved picture (BMP 481 KB) to a JPEG, just as the previous one, I used maximum (100%) quality. So when the picture turned out to be 342 KB, I phoned Doug asking why. Well, I did feel real stupid when I realised that the compression was reduced due to increased quality, so then I began experimenting with different compressions and formats.
The results were really surprising. I used PM View, a really good viewer program to try saving my Desktop picture in multiple JPEG qualities and a GIF format. The JPEG files ranged in size from 40 KB to 342 KB, but they were all much poorer in quality than the 104 KB GIF file. So that is what I used to store my desktop in.
I also tried saving the 40 KB JPEG as a GIF, but it turned into a 262 KB file. This was consistent with converting other JPEG compressed files.
I then concluded from this and previous knowledge that JPEG works well on photographs, and poorly on lines, that GIFs would be better for pictures with lines and JPEG may get a lot better compression on plain pictures. The most striking example was my monkey shot that was originally stored on my site as a 99 KB JPEG. I was able to reduce the quality to a acceptable level so that the file is now only 17 KB. Contrast that with the original BMP being 246 KB!! The GIF was also large at 206 KB.
I then converted all my BMPs to either GIF or JPEG, and some GIFs to JPEG. The 32 KB Space Walk GIF on my home page was reduced to under 6 KB. The 39 KB Sunset on my Vancouver page was reduced to 8 KB. Similarly, the line I use as a separator (below) was reduced to 428 bytes from 2243 bytes. Hopefully all the improvements will substantially reduce loading time for my pages.