画質を落とさずに画像を拡大する方法（2026ガイド）

Why Upscale Images

You need to print a photo but the resolution is too low. A client sent a logo that's 200 pixels wide and you need it at 800. You're creating a presentation and your screenshots look blurry when stretched. These are all cases where image upscaling helps.

Upscaling increases the pixel dimensions of an image. A 500x500 image upscaled 2x becomes 1000x1000. The challenge is filling in those new pixels in a way that looks natural and sharp.

Upscaling Methods Explained

Smooth (Bicubic): The default for most use cases. Analyzes surrounding pixels and creates smooth transitions. Best for photographs, gradients, and natural images. Produces a slightly soft result at high scale factors.

Sharp (Bicubic + Sharpening): Same base algorithm as smooth, but applies a sharpening convolution filter afterward. Good for text, graphics, screenshots, and any image where you want crisp edges.

Nearest Neighbor: Simply duplicates each pixel without any blending. Creates a blocky, pixelated look. This is exactly what you want for pixel art, retro game sprites, and QR codes where hard pixel edges must be preserved.

Best Practices

• Start with the best source. No upscaling algorithm can add detail that doesn't exist. A clear, well-lit photo upscales far better than a blurry screenshot.
• Don't exceed 4x. Beyond 4x, all methods produce noticeably soft or artifacted results. If you need very large output, find a higher resolution source.
• Match the method to the content. Photos get smooth. Text and UI get sharp. Pixel art gets nearest-neighbor.
• Save as PNG for graphics, JPG for photos. PNG preserves exact pixel values (important for text and pixel art). JPG is smaller and fine for photographs.

Upscale Images for Free

Our free Image Upscaler lets you enlarge images up to 4x with smooth, sharp, and pixel art modes. Everything runs in your browser using the Canvas API. No upload, no signup, no watermarks.