Resize Image by Percentage

A fixed target dimension makes sense when every image should end up the same size. Percentage scaling makes sense when they should not — a batch of photos taken at different resolutions, from different cameras or cropped to different degrees, where the goal is "smaller by the same proportion" rather than "all identical". Scaling a mixed batch to a single fixed width would leave a photo that started small barely changed and one that started huge still oversized relative to the others; a percentage treats every image consistently regardless of where it started.

Halving both dimensions removes about three quarters of the pixels, which is close to the point where the size reduction is dramatic but the result is still clearly a full-resolution image rather than a thumbnail — most photos intended for general viewing rather than large prints have far more resolution than they need, and 50% recovers a large fraction of that without the image looking obviously reduced. Going further, to 25% or below, starts to look like a thumbnail rather than a resized photo unless the source was unusually high-resolution to begin with.

A batch containing a 4000×3000 DSLR photo, a 3024×4032 phone photo and a 1600×1200 older camera photo, scaled to 50%, becomes 2000×1500, 1512×2016 and 800×600 respectively — each is proportionally half its own original, rather than all three being forced to match each other. That is the specific case percentage scaling handles and a fixed-dimension resize cannot: it respects however each source image started out.