Resize images with Irfanview

Irfanview can be used to resize image. With the image opened, click on IMAGE (highlighted with red ellipse) in the menu bar at the top of the program, then select RESIZE/RESAMPLE (or ctrl+R). You will get a "Pop-up" where you can enter the new width and/or height of the image. You may chose to keep the aspect ratio constant so that the image remain undistorted by ticking the box next to "Preserve aspect ratio" (highlighted with red ellipse), then typing in the new width (highlighted with red ellipse) and click "OK". See screenshot below:



The height will automatically change so that the image remain undistorted.

If you want to determine the width of the height of the resized image yourself, untick the box next to "Preserve aspect ratio". In this case, the image may become distorted (different from the original image).