BigDaddy Loc: Pittsburgh, PA

Supposedly Bicubic is best for upsizing, Bilinear better for downsizing. I rarely increase the dimensions of my pictures, but almost always decrease dimensions for display. Never noticed any issues downsizing. I routinely downsize from 6000x4000 to 1920x1080 with no issues. The opposite is not true however.

Lately I've done a bit of upsizing parts of photos and even whole photo's with good success, and I use Bicubic for both for no reason other than that's my editors default.

Jpg compression is a totally different animal and simply encodes repeated data and decodes it when decompressed. Since picture don't compress well because of so many similar but different colors, jpg figured out how to re-code similar colors that hopefully the human eye can't discern. It does a superb job of this until you get to pretty high compression levels, like 60%, then you start to notice some issues. Compression changes just file size, not dimensions.

Architect1776 Loc: In my mind

[quote=BigDaddy]Most editors let you resize your photo to whatever you want, and show the before and after file size as well. I often use the free browser/editor FastStone to do this. You can punch in any number[s] you want and it will give you the new file size. For example, I just loaded a 6000x4000 9mb picture and resized it to 3000x2000 and it came up with 6mb file size. Changing to 2700x1800 gives 4.86MB.

This will not degrade your picture at all, or not to any noticable degree, but will make the picture smaller, but big enough for even 4k displays.

FastStone is super easy to use for this. Just open your pic in FastStone, Press Ctrl+R and punch in the numbers while maintaining the aspect ratio. It will show the original and new file size for you.

Changing the compression ratio will also change the file size, but will start to degrade quality pretty quick. For printing or a contest, I I'd leave the compression ratio low, at least 8 or 10.[/quote]