I have images that are rendered via color map system. The larger images have a smaller file size then that of the thumb image which is re-sized. Which images should I display for the end user? Would it be more convenient to show the smaller file size image with thumb dimensions or the small dimension image with larger file size? Multiple images would show on a page and I ask because I understand scaling larger file dimensions down can cause performance issues. 
When large dimension images have smaller file size than thumbnails, which version should I display?
php;images;performance
scaling larger file dimensions down can cause performance issuesThe performance issue is because the larger image is usually a much larger file size and downloading the much larger file over HTTP is the significant bottleneck.But you're saying the larger image is the smaller file size?! How does that work? If that really is the case, and this larger (but smaller file size) image is compatible with all the browsers you are concerned about then you only need the single larger image (smaller file size). Browsers/computers are speedy beasts these days; scaling a larger image down to thumbnail size is not an issue and is infinitely quicker than downloading another image over HTTP.In the past, browsers did not do a very good job of scaling images - the quality was not very good (simple pixel resize for the sake of performance). However, all remotely modern browsers use better algorithms and the quality is good.