For heavy duty image processing, ImageMagick does the job. Point and click is great for tweaking a few images, but if hundreds or tens of thousands are to be processed, then go for a tool that can be scripted.
ImageMagick provides a command line tool called ‘convert’ or ‘magick’ that takes multiple options and can operate on lists of images. Resize is one of 5 transforms provided, and transform is just one of 40-odd other image operation groups supported.
Rather simple when you know how to resize all the images on a computer and then montage or animate the result.
Need to convert an US Mil Standard CALS file to a TIFF – no problem.
This bad boy is typically behind the scenes on a web-server or photo repository. Key advantages: comprehensive, can be automated, and is made to handle images in bulk; powerful! Disadvantages: though simple usage is straightforward, users have to learn how to drive and have a good understanding of image processing for advanced work. Scripting not ideal when a single image has to be tarted up experimentally, because a point and click interface often supports suck it and see better.
Dave