How to resize a screenshot image on a Mac so that it is "regular size" when posted on the Internet? Short question: why if I do screenshot on a Mac and crop it, and see it using Preview, it is a good size but when posted to Internet, such as StackOverflow, its width and height always double? I can resize 50% width and height but the image is not as clear (not retina). So how can I use that image and not have it show up twice the width and height?)



I sometimes take a screenshot on a Mac (OS X Mavericks), by CMD-Shift 4, and resize it to 50% width and height in Preview.

But when posted on the Internet (for example, on an online forum or on ibb.co or imgur.com) , it is double size again. I tried 50% and then resolution changed from 144 to 72 for the original image, and the same: it is still double size.  I had to do a 25% and also 72, in order that it is the proper size.

It is really weird. Why 25% and not 50%, and how does the 144 or 72 matter? (or does it?)
I'm not quite sure what you mean. I tested it with a screenshot (see above) and reduced the resolution to half, uploaded it here, it's still the new resolution that I chose in Preview.

Maybe you can try the following:


Change the resolution in Preview 
Close the image
Right click on it, check Get Info, then "More Info", there you should find the current resolution which should be slower than before
If this does not work for you, maybe try a tool like ImageMagick that offers a lot of options for manipulating images.


http://cactuslab.com/imagemagick/