Karuku Prototype

Keep the light.
Lose the weight.

Smaller JPEGs, with HDR data intact.
Processed entirely on your device.

A little lighter. Still your photo.

JPEG / HDR JPEG

Your photos never leave your device

JPEG only for now. HEIC conversion is not supported.

A JPEG compressor that keeps HDR data.

Karuku is a free image compressor for people who want a smaller photo, not flatter highlights. Optimize one JPEG at a time in your browser, compare it with the original, then download or share it. Your photo is processed on your device, never uploaded to an image-processing server.

How does Karuku preserve HDR?

Supported Ultra HDR and Apple HDR JPEGs contain a base image and an extra image called a gain map. Karuku recompresses the base while keeping the original gain map, color profile and orientation data. It verifies the output before export. Compression is lossy, so preserving HDR data does not mean every pixel stays identical.

Which photos can I compress?

This prototype supports ordinary JPEGs and compatible gain-map HDR JPEGs up to 16 megapixels and 40 MiB. HEIC, HEIF, AVIF, PNG and video are not supported yet. Karuku does not resize or crop your photo, and stops rather than silently converting unsupported HDR to SDR.

Are my photos private?

There are no photo uploads, analytics or ads. Processing happens locally with WebAssembly. Your original file is unchanged, and photos are not saved in the offline cache. EXIF metadata, including location, is preserved in the output: review it before sharing. Downloading or sharing a file is always your choice.

Does it work on iPhone, Android and offline?

Karuku is designed for mobile browsers and works on desktop too. After the first setup, it can run offline and be added to your home screen. Sharing and HDR display depend on your browser and device. HEIC conversion is not available, and a phone photo picker may convert an image before Karuku receives it.

Will HDR survive an Instagram Story?

Karuku verifies HDR data in its exported JPEG, but HDR after posting to Instagram Stories has not been verified. Instagram may process the file again. Keeping HDR in a downloaded image and showing HDR after an upload are separate things.

What stays. What changes.

Karuku is a prototype that makes JPEGs smaller without uploading your photos.

Keep the data that makes HDR shine.

Ultra HDR and Apple gain-map JPEGs are supported. Only the base image is recompressed; the HDR gain map, color profile and orientation data are kept. Compression is lossy, so the result is not pixel-identical to the original.

Unsupported photos stay untouched.

This version does not support HEIC, HEIF, AVIF, video, or photos above 16 megapixels or 40 MiB. If HDR preservation cannot be verified, processing stops instead of silently converting to SDR.

Posting is a separate step.

Karuku checks HDR data in the output file, but HDR after posting to Instagram Stories has not been verified. Your phone may also convert a photo when you select it. HDR data lost before import cannot be restored.

Your photos stay on your device.

No photo uploads, analytics or ads. Your original file is never modified. EXIF metadata, including location, is also preserved, so review it before sharing.

Offline use is available after the first setup completes. Download locations and sharing options depend on your operating system.