JP2 to ICO Converter
Convert JP2 to ICO in your browser. JP2 files usually come from libraries and digital archives, medical (DICOM) and satellite imaging, and digital cinema packages; ICO is the better fit for favicons and Windows icons. You get a multi-size ICO with PNG-compressed icons (16, 32, 48 and 256 px by default). Nothing is uploaded.
- Processed locally
- No upload, no wait
- No sign-up
- No watermark
Drop images here
or choose files · paste with Ctrl/⌘ V
JP2 expected · other image formats also work
How to use JP2 to ICO
- 1
Add your JP2 files: drop them here, choose them, or paste from the clipboard.
- 2
Choose the icon sizes to include.
- 3
Click Convert. Each file is decoded and encoded in a background thread on this device.
- 4
Download the .ico files one at a time or together as a ZIP.
Why use Aback Images for jp2 to ico
Where the ICO goes next
ICO opens in every browser (as a favicon), Windows and most Linux desktops.
ICO next to JP2
Both sides are lossless, so the size depends on how well the ICO encoder handles this picture compared with the JP2's wavelet coding: reversible 5/3 for lossless files, irreversible 9/7 for lossy ones.
Written without a lossy pass
The ICO is written losslessly, so the pixels decoded from the JP2 arrive unchanged, apart from precision beyond 8 bits per channel.
Processed on your device
Your images are decoded, edited and encoded inside this browser tab by Web Workers. Nothing is uploaded to a server.
JP2 vs ICO
What changes from JP2 to ICO
Encoding: the JP2 uses wavelet coding: reversible 5/3 for lossless files, irreversible 9/7 for lossy ones; ICO uses each size stored as a headerless BMP or as a complete PNG, and the download is a multi-size ICO with PNG-compressed icons (16, 32, 48 and 256 px by default).
Bit depth: up to 16 bits per channel is common, more is possible in the JP2; ICO allows 1 to 32 bits per pixel, set per size, and the ICO written here has 32 bits per pixel. 12 and 16-bit JPEG 2000 files are reduced to 8 bits per channel.
Colour: sRGB, greyscale, YCC or a space described by an ICC profile in the JP2; ICO supports RGB or a palette, per image, written here as 8-bit sRGB.
Transparency: the JP2 stores it as an extra component flagged as opacity; the ICO keeps it as 8-bit alpha in 32-bit and PNG entries, or a 1-bit mask in old icons.
Metadata: the JP2 can carry XML, ICC and resolution boxes; ICO can carry only a directory of the sizes inside, with no EXIF, but nothing is copied across.
About JP2
JPEG 2000 is a wavelet-based format that can be truly lossless or lossy, handles very high bit depths and huge images, and is used where long-term fidelity matters: archives, medicine, satellites and digital cinema.
A .jp2 file is a box structure: a 12-byte signature box, an 'ftyp' box, a 'jp2h' header box with the size and colour specification, then the 'jp2c' box holding the codestream, which begins with FF 4F FF 51.
JP2 files usually come from libraries and digital archives, medical (DICOM) and satellite imaging, and digital cinema packages.
About ICO
ICO is a container that bundles several sizes of the same icon (16, 32, 48, 256 px) into one file. It is still the most compatible format for website favicons and Windows app icons.
An ICO starts with a 6-byte ICONDIR (type 1 for icons) and a 16-byte entry per image giving width, height, colour count and offset. Each image is either a BMP without its file header plus an AND mask, or a complete PNG.
When converting JP2 to ICO makes sense
ICO is the better choice for favicons and Windows icons, while JP2 suits archival masters and specialist imaging.
ICO strengths: Multiple sizes in one file; Required by Windows and supported by every browser as a favicon. Drawbacks to weigh: Max 256×256 per image; Not for photos.
Limitations
- A JPEG 2000 file may be a lossless master or a lossy derivative; the file does not tell you which at a glance, so keep the original either way.
- Archival scans can be tens of thousands of pixels across, and decoding them needs a lot of memory on a phone.
- Each size inside the ICO is scaled from your image, and detailed artwork loses legibility at 16 and 32 px, so simplify logos first.
- Non-square images are centred on a transparent square for each icon size.
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Frequently asked questions
Does converting JP2 to ICO lose quality?
ICO is written losslessly, so the pixels are stored exactly as decoded. 12 and 16-bit JPEG 2000 files are reduced to 8 bits per channel.
Is transparency kept in the ICO?
Yes. JP2 stores it as an extra component flagged as opacity, and the ICO is written with an alpha channel, so transparent areas stay transparent.
Which icon sizes are included?
16, 32, 48 and 256 px by default, the set Windows and browsers expect. You can choose other sizes. Non-square images are centred on a transparent square.
Which apps open ICO files?
Every browser (as a favicon), Windows and most Linux desktops.
Are my images uploaded anywhere?
No. Processing happens inside your browser with WebAssembly and Web Workers. The site only downloads the app code and codecs; your files never leave your device. You can confirm this with the live upload counter on the tool, or in your browser's network panel.
Can I process many files at once?
Yes. Drop a whole selection or folder. Files are processed in parallel on several worker threads, each result can be downloaded on its own, and everything can be saved as one ZIP.
Is it free? Is there a file limit or watermark?
It is free with no account, no watermark and no daily limit. The only limit is your device's memory: very large images (over roughly 100 megapixels) may be refused to keep the tab from crashing.