For picture sharing websites that make thumbnails of pictures you upload - is it something relatively straightforward like take one out of every so many pixels? I want to see if I can get a picture of one thing to generate a thumbnail of another thing.

2/14/2009 12:58:43 PM

taking "one out of every so many pixels" will result in wicked moire patterns on a lot of images and would be a rarely used technique, generally interpolation is used to minimize artifacting and loss of signal

http://www.cambridgeincolour.com/tutorials/image-interpolation.htm

2/14/2009 1:42:00 PM

most of them use GD or imagemagick

download the sources and take a look at how they do their scaling

2/14/2009 1:50:55 PM

the most common method is bilinear or bicubic interpolation, often with a pre/post blur to eliminate moire artifacts.

2/14/2009 5:25:23 PM

^we have a winner.

The best thumbnail generators actually use a hybrid of 2 or 3 processes. Depending on the composition of an image, both in contrast and color, bicubic is generally the best option, but a bilinear+filter approach can sometimes give you a better reduction.

2/14/2009 7:04:33 PM

So then I'm probably not going to get this to work

2/14/2009 7:34:14 PM