How to choose among the three resize methods?
By pixels: set the exact target width and height. Best when you have explicit size requirements, such as platform limits or print dimensions.
By percentage: scale the whole image relative to its original size — for example shrink to 50%. Best for quickly reducing file size.
Preset sizes: built-in common specs (such as 1920, 1280, 800, 640), handy for everyday needs like web illustrations.
Why lock the aspect ratio?
An image has a fixed aspect ratio. If you set width and height independently, they may not match the original ratio, stretching the image out of shape.
With aspect ratio locked, changing the width automatically computes the height from the original ratio (or vice versa), so the image never gets stretched.
Does enlarging an image make it blurry?
Yes. A bitmap consists of fixed pixels; enlarging only interpolates extra pixels by software, adding no new detail, so the enlarged image turns blurry.
Web display usually calls for shrinking images, not enlarging. When you need a large crisp image, generate it from the source (a vector format or the original file) instead of upscaling a small image.