Runs 100% in your browser · nothing uploaded
Edge-aware upscaling, adaptive sharpening and optional cleanup, running on your own device. Free, with no sign-up and no watermark.
1200 × 800 Toggle: press T or hold Space in the viewer
Example: a 1200 × 800 crop of a 960 × 636 photo enlarged to 3840 × 2544; press 100% to see it pixel for pixel. Drop your images anywhere on this window, or use Add images.
Scale2x/3x smooths diagonal steps; nearest neighbour keeps square blocks. Neither adds colours.
Output
Auto saves JPG, or PNG for images with transparency and for pixel art.
For JPG, WebP and AVIF. PNG ignores it: it is always lossless.
Your images appear here. Nothing is uploaded.
Select an image to view it or give it its own settings. Drag images, or use the arrow buttons, to change the order. Press ? for keyboard shortcuts.
→
Toggle: press T or hold Space in the viewer
Works in Chrome, Edge, Firefox and Safari, on computers and phones.
Everything included
Every step runs on your graphics chip or processor, in your browser. Each picture below is real output of the engine.
1200 × 800 Toggle: press T or hold Space in the viewer
Edge-aware upscaling (EASU) enlarges along the edges in steps of at most 2×, and adaptive sharpening (RCAS) runs after every step. The same 960 × 715 photo, enlarged to 3840 × 2860, compared with a standard resize.
Measures the noise first, then smooths it with an edge-preserving filter; High also removes JPEG blocks.
White balance, levels, exposure, shadows, highlights, vibrance and clarity, with a live preview.
Whole-pixel scaling for sprites: hard edges and no new colours.
Up to 10 images at a time, each with the batch settings or its own. Download them one by one or together as a ZIP, as JPG, PNG, WebP or AVIF.
From file to 4K in your browser
Four steps. The first and the last are yours; the middle two run on your device.
Drop, paste or pick up to 10 JPG, PNG, WebP or AVIF images, 20 MB each. They are read from your disk, not uploaded.
Pixel art is detected, images already at 4K are skipped, and sizes too big for this device are flagged before anything runs.
Cleanup, edge-aware upscaling, adaptive sharpening and colour & light run on your graphics chip, with live progress.
Compare with the original at 100%, then save each image or all of them as a ZIP, as JPG, PNG, WebP or AVIF.
Measured with the engine itself; see how these numbers are produced.
Image quality comparison
A standard resize spreads every pixel over a larger area and blurs the edges. 4K Images enlarges along the edges and sharpens them as it goes. It does not invent detail that the photo never had.
600 × 400 Toggle: press T or hold Space in the viewer
600 × 400 Toggle: press T or hold Space in the viewer
600 × 400 Toggle: press T or hold Space in the viewer
Inside the engine
EASU, from AMD FidelityFX Super Resolution 1, reads the direction of the edges around every pixel and enlarges along them, so outlines stay crisp instead of turning soft. It runs on your graphics chip in steps of at most 2×.
1.1 s *
1920 × 1080 → 3840 × 2160 with default settings, on an AMD Radeon RX 5500 XT
+3.3% *
edge contrast at 4K with the default settings, compared with a bicubic resize
360 × 240 Toggle: press T or hold Space in the viewer
Round trip (each sample halved with Lanczos3, then enlarged ×2 and compared with the original): SSIM 0.884 vs 0.878 for bicubic; PSNR 26.61 dB vs 26.48 dB. EASU alone (sharpening off) gives 0.995× the edge contrast of bicubic at 4K: its gain is cleaner, straighter edges rather than stronger ones. Each sample enlarged to 4K with default settings and with sharpness 0, and with bicubic; mean Sobel gradient on the edges of the bicubic output (its strongest 10%), as a ratio.
RCAS adds sharpness in proportion to local contrast and stops before it would overshoot, so it adds no halos, and flat areas such as skies are left alone. It runs after every enlargement step, while edges are still narrow.
+3.8% *
edge contrast at 4K with sharpness 35, compared with sharpening off
0–100 *
sharpness is yours to set; 0 turns it off
360 × 240 Toggle: press T or hold Space in the viewer
Round trip: SSIM 0.884 with sharpness 35 vs 0.881 with sharpening off; PSNR 26.61 dB vs 26.56 dB. Judge sharpness at 100% zoom: at Fit the image is scaled down and the difference is hard to see.
The engine first measures how noisy the image is, then smooths the noise with an edge-preserving bilateral filter; High also removes the 8×8 blocks left by heavy JPEG compression. Because the filter scales to the measured noise, clean images keep their texture.
−57% *
noise (σ 19.8 → 8.5) on a flat patch of the noisy test image, cleanup High
19.8 → 14.6 *
the same patch with cleanup Low
360 × 240 Toggle: press T or hold Space in the viewer
White balance, exposure, levels, shadows, highlights, vibrance, saturation and clarity, applied on your graphics chip after sharpening. Everything is off by default, and a preset only moves the sliders you can see.
10.2 → 2.2 *
ΔE2000 of a grey patch under a colour cast, before → after auto white balance (lower is more neutral)
×1.99 *
linear brightness after +1 EV of exposure (exactly ×2.00 would be ideal)
360 × 240 Toggle: press T or hold Space in the viewer
For sprites and pixel art, the image is enlarged in whole-pixel steps with Scale2x/Scale3x or nearest neighbour, so edges stay hard and no new colours appear. Sharpening, cleanup and colour are switched off in this mode.
0 *
new colours in a 3840 × 3840 output of a 5-colour sprite
5792 / 4096 px *
largest square output on a computer / on iPhone and iPad (memory limit)
128 × 128 Toggle: press T or hold Space in the viewer
* Measured on 2026-09-24 with Chromium 153.0.8010.12 on an AMD Radeon RX 5500 XT (Intel(R) Core(TM) i7-9700K CPU @ 3.60GHz), using the three CC0 sample photos and synthetic test images; timings vary with the device. How these numbers are produced.
Everything is included
Free
The work happens in your browser, on your own processor and graphics chip, so there are no servers to pay for, and nothing to charge you for.
Credits
EASU and RCAS: the edge-aware upscaler and the adaptive sharpener, ported to WebGL2.
Source code of AMD FidelityFX Super Resolution 1MozJPEG, libwebp, libavif and OxiPNG compiled to WebAssembly: the encoders for every download.
Source code of Squoosh codecs, via jSquashLanczos3 resizing: for reductions, and the enlargement fallback when WebGL2 is not available.
Source code of picaBuilds the ZIP of a whole batch in your browser.
Source code of fflateThe full licence texts are in the third-party notices.
Tools
Every tool runs in your browser. Nothing is uploaded.
Fit any photo to a desktop, ultrawide, phone or tablet screen size.
Make JPG, PNG, WebP and AVIF files smaller and see the real size saved.
Change the format of JPG, PNG, WebP, AVIF, GIF, BMP and HEIC images.
Exact sizes, percentages, aspect-ratio crops, rotation and straightening.
See the resolution, camera data and location, and remove them without quality loss.
Put text or a logo on your images, in one place or tiled.
Get the main colours of an image as HEX, RGB, HSL and OKLCH.
Answers
About privacy, sizes, formats and what the engine can and cannot do.
Every step of the engine, how the numbers on this page are measured, and the open-source credits.
Add an image and download a sharper, bigger version in seconds. It never leaves your device.
