Commands for ImageMagick to create thumbnails

Question

Given an photograph uploaded by a user, what is best approach to creating a number various sized thumbnails Using ImageMagick (or GraphicsMagick)? My guess to the steps:

1. Create a super sample of the image, maintaining original aspect ratio
2. Apply watermark to super sample
3. Create the various sized thumbnails using the watermarked super sampled image

Additional requirements:

1. Best quality possible (does this mean PNG over JPG?)
2. Smallest file size possible (does this mean JPG over PNG?)
3. Use density of 72x72, units is ppi

Since I am not that familiar with the intricacies of IM (or GM), some guidance to the best commands that meet my objectives would be highly appreciated. Thanks.

Answer 1

Check out the ImageMagick documentation:

• For a specific size http://www.imagemagick.org/Usage/thumbnails/#fit
• For watermarks http://www.imagemagick.org/Usage/annotating/#watermarking

The best quality possible is complicated since difference images compress differently. I'm partial to PNG since it has a variety if compression techniques available to allow for experimentation.