A free program for Android, by TechAmongus.

If you want to reduce the size of your images and you don’t want to lose any quality, then you should try this app. It’s simple to use and works perfectly. You just have to select the image that you want to resize and then adjust it till you reach your desired size. After that, you can resize it by choosing the height or width of the photo. The other option is for cropping the image.

After that, you can save the resized photo in the selected directory.