How do I resize images without a loss in quality?

"If you mean so that you can zoom in and see the same quality as you did when it was 2010 x 1080, you can't, this is impossible.

Imagine a 3x3 grid with the following (r=red, g=green, b=blue):

bgr
grb
rbg

If you then want to change it to a 2x2, it will do something like this (b=blue, y=yellow, p=purple):

bp
yp

Then, when you try to stretch it again, it will try to restore the colors, fill the gaps and work out what should be in certain places.

It is nearly always the case that the quality loss isn't that visible when you zoom in only slightly, but it is always the case, and if you are going from 2010x1080 to 338x450, you certainly will see it.

Also, if you were simply changing the size from 2010x1080 to 338x450, it is possible that you were distorting the aspect ratio which is a completely different issue.

You may want to look in to cropping the images instead, basically (image manipulation software dependent), drag a square around the parts of the image you want then just keep that part.

Also, when you have a selection or image you want to shrink, some utilities allow you to lock ratio, if your software doesn't, just remember to divide by the same ammount, for example a half size 2010x1080 would be 1005x540."

There is no way you can do it IMO. Smaller resolution will always result in a quality loss. Some pixels will inevitably be lost.
There is no way you can do it IMO. Smaller resolution will always result in a quality loss. Some pixels will inevitably be lost.

"Since you're dealing with raster images here, continuous scaling simply doesn't work. The only way it could possibly work like you expect would be to use higher-level mechanisms to scale your image, such as in HTML

<img src='foo.jpg' width='338' height='450'>

That way the browser would have the full-size image and does the scaling for you while the complete image would still be retained behind the scenes and could be used.

Note that HTML was an example, I have no idea what you are using the image for. You could also try fiddling with the dpi settings of the image so that it displays smaller in contexts like printing while still being the same pixel size.

But you definitely don't want to scale the image itself if you want to regain the full resolution at a later time."

"I think it's impossible not to lose quality if you are working with JPEG. JPEG is a format which compress the images in exchange to ""destroy"" some information.

Try to use another format first (let's say PNG for instance), which also compress the image but does not destroy any information. Anyway, as all the previous replies told you, you are going to get a physically smaller image, so it's impossible not to lose quality.

For image manipulation, GIMP is great. You can have it for Windows, Linux and OS X."