Krupno

Krupno is a free AI image upscaler for Windows. It enlarges photos and other images ×2, ×4 or to any size with neural networks, in a window (Krupno.exe) or from the command line (krupno-cli.exe). No account, no subscription, and your images stay on your computer.

A 300×200 photo (AI-generated) upscaled ×4 with "Photo, maximum detail": the original on the left of the slider, the result on the right.

Download Krupno for Windows: an installer or a portable ZIP, see Download and install.

• Runs on any DirectX 12 GPU (NVIDIA, AMD or Intel, integrated ones included) and falls back to the CPU. On Windows 11 24H2 and later it can also use the GPU and NPU vendors' accelerators, such as NVIDIA TensorRT-RTX and Intel OpenVINO.
• The installer offers models for photos (fast or with the most detail), for text and documents and for removing noise; other ONNX models work too.
• Large images are processed in tiles that fit in video memory, without visible seams.
• Keeps transparency, EXIF rotation and color profiles. Reads PNG, JPEG, TIFF, BMP, GIF, WebP and HEIC; writes PNG, JPEG, TIFF and BMP.
• Upscales animated GIF and WebP frame by frame into an animation of the same format, with the same timing.
• Works offline: apart from an update check you can turn off, it sends nothing over the network.
• The window speaks 16 languages.
• Needs Windows 10 1903 or later, x64.

Download and install

Get the latest version from Releases:

• Installer (Krupno-<version>-setup-x64.exe, recommended). By default it installs Krupno for the current user, to %LOCALAPPDATA%\Programs\Krupno, without administrator rights; "for all users" installs it to Program Files. .NET comes with it, so nothing else needs to be installed. During setup you pick the models to download, and optionally:
  • a desktop shortcut;
  • the install folder in PATH, so krupno-cli runs from any console;
  • "Upscale with Krupno" in the Explorer context menu of images and folders.
• Scoop: scoop bucket add krupno https://github.com/FLABER87/krupno, then scoop install krupno/krupno. It installs the portable ZIP with the default model; krupno-cli is on the PATH, and the models you add to its models folder are kept on updates (scoop update krupno).
• Portable ZIP (Krupno-<version>-win-x64.zip): unpack it and run Krupno.exe. It comes without models: download them from the models-v4 release into its models folder or into %LOCALAPPDATA%\Krupno\models.

The files are not code-signed yet, so Windows SmartScreen may warn on the first launch ("More info" → "Run anyway"). Each release has a SHA256SUMS.txt to check the downloads against. Uninstalling keeps your settings, logs and own models in %LOCALAPPDATA%\Krupno.

Window

Drop images or a folder into the window, click "Select files", paste with Ctrl+V or use "Upscale with Krupno" in Explorer. Then pick a model, a scale and a format, and click "Upscale".

• Strength (10–100%) blends the network's result with a plain resize, to tone down the textures a model invents and its oversharpening.
• Remove noise runs a separate model on the image before upscaling, to clean camera noise and grain that the upscaler would keep or turn into invented texture. It is slower and smooths fine texture as well, so it is off by default. With "Other" set to a scale of 1, it only removes the noise. It needs the SCUNet model, which the installer offers.
• Scale: ×2, ×4 and so on, or "Other" for a scale of your own or a width, height or long side in pixels.
• Comparison: a slider or two frames side by side; the mouse wheel zooms, a double click toggles "Fit to window" and 1:1.
• A batch is shown as a strip of thumbnails with each file's status.
• Settings (the gear button, or Ctrl+,): the device and tile size ("Auto" by default), "Seamless tiles", "Test-time augmentation", the language and the update check. Under "Results": what happens to a result that is already there from an earlier run (by default it is kept and the new one gets a number, photo_x4 (2).png; or it is replaced, or the image is skipped), and "Add the model to the file name" (photo_x4_4xBHI_dat2_real.png), so the results of different models don't replace each other. The version is at the bottom of the window.
• If something fails, "Copy error details" puts what a bug report needs on the clipboard. The window's logs are in %LOCALAPPDATA%\Krupno\logs.

Keys	Action
Ctrl+O	open files
Ctrl+V	paste files or an image
Ctrl+Enter	upscale
Esc	cancel processing
Ctrl+0 / Ctrl+1	fit to window / pixel for pixel
Ctrl+Plus / Ctrl+Minus	zoom in / zoom out
Ctrl+C	copy the result
Ctrl+,	settings

Command-line tool

krupno-cli photo.jpg                               # → photo_x4.png next to the source
krupno-cli photo.jpg -s 2 -f jpg -q 92             # ×2 result as JPEG
krupno-cli C:\photos -o C:\photos_x4               # a whole folder
krupno-cli C:\photos -r -o D:\x4 --skip-existing   # subfolders too; only the images without a result
krupno-cli photo.jpg -m 4xBHI_dat2_real_fp16 --name-model   # → photo_x4_4xBHI_dat2_real.png
krupno-cli photo.jpg --long-side 3840              # 3840 px on the longer side
krupno-cli photo.jpg --denoise                     # remove noise first, then ×4
krupno-cli photo.jpg --denoise -s 1                # only remove noise
krupno-cli cat.gif -s 2                            # → cat_x2.gif, every frame ×2
krupno-cli --list-models --list-devices

krupno-cli --help lists every option. A result never replaces a source image; one from an earlier run is replaced unless --no-overwrite (the new one gets a number) or --skip-existing is given. Without -m, the default model is used (marked with an asterisk in --list-models).

Models

Krupno runs ONNX upscaling models. The installer downloads the ones you tick from the models-v4 release; the ZIP comes without them.

Model	In the window	License	Time¹
4xBHI_realplksr_dysample_real	Photo, fast (default)	CC BY 4.0	6.7 s
4xBHI_dat2_real (fp16 and fp32)	Photo, maximum detail	CC BY 4.0	33 s (fp16)
4x-UltraSharpV2	General purpose	CC BY-NC-SA 4.0, non-commercial only	42 s
4x_foolhardy_Remacri_fp16	Text and documents	CC BY-NC-SA 4.0, non-commercial only	5.8 s
RealESRGAN_x4plus (fp16 and fp32)	Classic	BSD-3-Clause	4.6 s (fp16)
realesr-general-x4v3	Draft	BSD-3-Clause	1.6 s

¹ A 1920×1200 photo upscaled ×4 on an RTX 3080.

The installer also offers scunet_color_real_psnr_fp16, the model of "Remove noise" (--denoise): SCUNet, which removes noise at the original size before the upscaler runs, in about as much time again as the default model. It helps most with Remacri, which keeps noise as it is; see Noise.

Models make small text sharp, but they may also change it, digits included. Remacri keeps small text best and is worse than the others on photos; see Text. Check important numbers against the original whatever the model.

Each model has its own license, which Krupno's MIT license does not cover:

• The BHI models are by Philip Hofmann (Phhofm/models), under CC BY 4.0: commercial use is allowed, with attribution.
• UltraSharpV2 is by Kim2091 and Remacri by foolhardy (OpenModelDB), both under CC BY-NC-SA 4.0: non-commercial use only. The window marks them as such.
• The Real-ESRGAN models are by Xintao Wang (Real-ESRGAN), under the BSD 3-Clause license.
• SCUNet, the model of "Remove noise", is by Kai Zhang (cszn/SCUNet), under the Apache 2.0 license.

Other models work too: put .onnx files into %LOCALAPPDATA%\Krupno\models ("Open models folder" in the window). To convert PyTorch weights (.pth, .safetensors), use tools/convert_to_onnx.py; see docs/models.md for how, where to get weights and how the models compare. Community models, for example from OpenModelDB, each have their own license, and many are for non-commercial use only.

Updates

At startup the window asks github.com which release of Krupno is the latest: one request that carries only the app's version. If there is a newer one, a line above the settings says so:

• in an installed copy, "Update" downloads the new installer, checks it against the release's SHA256SUMS.txt and installs it in the same mode (for you or for all users), keeping your models and choices;
• the portable ZIP links to the release page instead.

Nothing is downloaded until you click "Update". To turn the check off, clear "Check for updates" in "Settings".

Building

Requires the .NET SDK 10.

dotnet build Krupno.slnx -c Release
dotnet test tests/Krupno.Core.Tests -c Release

More for contributors in docs/:

• development.md: layout, tests, CI and translations;
• installer.md: the installer, the portable ZIP and releases;
• models.md: converting models to ONNX and how they compare;
• how-it-works.md: tiling, memory, accelerators, color and the finer points of the window and the command-line tool.

Feedback

Found a bug or missing something? Open an issue; questions and ideas are welcome in Discussions. If Krupno is useful to you, a star on GitHub helps other people find it.

License

The code is under the MIT license, see LICENSE. It does not cover the models: each has its own license (see Models). The components Krupno ships with and the models it can download are listed in THIRD-PARTY-NOTICES.txt.