I am looking for a program that can Scale images by a factor of around a 1.5 -2x scale factor. I haven't seen any programs that aren't behind a paywall. Any help would be appreciated, thank you.
I like to use GIMP image editor. GIMP is a free, cross-platform image editor available for GNU/Linux, OS X, Windows and more operating systems. It has a toolbox full of useful tools for manipulating an image after you have rescaled it.
Also useful with GIMP is another app named Simple Screen Ruler. This app displays a ruler on the screen. You can measure objects with a ruler that is shown on the screen. Download this app from Microsoft Store for Windows 8.1 and Windows 10.
I'm surprized no one mentioned ImageMagick, it's the reference in command-line FOSS softwares for image edition, specially batch edition. It's cross-platform and present by default in many Linux distributions. Definitively a must.
Check out a-sharper-scaling, I've been using it with good results, also it's free-ware.
There is a free and open source command line tool GraphicsMagick
It allows to manipulate images from command line, including resizing.
If it´s only about Windows here some tools that can be useful:
Image Resizer for Windows Older users might remember PowerToys from the days of XP and Windows 95. In 2019, Microsoft resurrected PowerToys as an open source project for Windows 10. One of the returning features is the image resize tool which is based on Image Resizer for Windows from Brice Lambson. You can use either software on Windows 10 but Image Resizer is the only one that works on Windows 7 or 8.
FastStone Photo Resizer FastStone’s tool is a powerful program for batch converting images. It also has a dedicated batch renaming function in case you don’t want to change the files but give them more orderly names. Photo Resizer includes its own file browser in addition to the standard drag and drop, and the amount of supported images is quite large with Photoshop PSD files and ICO icon files also included. There are seven output image formats, one of which is PDF.
XnResize XnResize is essentially the batch image resizing part of XnConvert ported into a standalone program. As that is our goal here, we’ll look at XnResize but if you want more features, try XnConvert. XnResize and XnConvert are available for Windows (setup installer or portable version), Mac, and Linux.