Scale2x Upscaler

Scale2x (also known as EPX or AdvMAME2x) doubles pixel-art resolution by looking at each pixel's four neighbors: when two adjacent neighbors match, the corresponding corner of the output block copies that color, smoothing staircase diagonals into cleaner slopes. It was developed for the AdvanceMAME emulator to upscale arcade graphics in real time.

Nearest neighbor turns every pixel into an identical block — faithful but blocky on diagonals. Scale2x rounds those diagonal steps. Because it never introduces new colors, the result still reads as pixel art rather than a blurry photo upscale.

For in-game assets where the engine scales sprites, or when you want the authentic chunky look — use nearest neighbor then. Scale2x shines for promo art, video thumbnails, and printing pixel art at larger sizes. Dithered areas can look uneven since the algorithm treats dither patterns as edges.

It's the real EPX/Scale2x rule set (and Scale3x for 3x). For comparison this page also offers nearest neighbor and a simplified HQ2x — switch algorithms after uploading to see the difference on your own image.