ICO to JP2 Converter
Convert ICO to JP2 in your browser. ICO files usually come from website favicons, Windows programs and installers; JP2 is the better fit for archival masters and specialist imaging. You get a lossless JPEG 2000 (.jp2) using the reversible 5/3 wavelet. Nothing is uploaded.
- Processed locally
- No upload, no wait
- No sign-up
- No watermark
Drop images here
or choose files · paste with Ctrl/⌘ V
ICO expected · other image formats also work
How to use ICO to JP2
- 1
Add your ICO files: drop them here, choose them, or paste from the clipboard.
- 2
There is nothing to tune: the JP2 is written losslessly. Resizing and rotating are under More options if you need them.
- 3
Click Convert. Each file is decoded and encoded in a background thread on this device.
- 4
Download the .jp2 files one at a time or together as a ZIP.
Why use Aback Images for ico to jp2
Where the JP2 goes next
JP2 opens in macOS Preview, GIMP, IrfanView, XnView, ImageMagick and the OpenJPEG tools.
JP2 next to ICO
Both sides are lossless, so the size depends on how well the JP2 encoder handles this picture compared with the ICO's each size stored as a headerless BMP or as a complete PNG.
Written without a lossy pass
The JP2 is written losslessly, so the pixels decoded from the ICO arrive unchanged.
Processed on your device
Your images are decoded, edited and encoded inside this browser tab by Web Workers. Nothing is uploaded to a server.
ICO vs JP2
What changes from ICO to JP2
Encoding: the ICO uses each size stored as a headerless BMP or as a complete PNG; JP2 uses wavelet coding: reversible 5/3 for lossless files, irreversible 9/7 for lossy ones, and the download is a lossless JPEG 2000 (.jp2) using the reversible 5/3 wavelet.
Bit depth: 1 to 32 bits per pixel, set per size in the ICO; JP2 allows up to 16 bits per channel is common, more is possible, and the JP2 written here has 8 bits per channel.
Colour: RGB or a palette, per image in the ICO; JP2 supports sRGB, greyscale, YCC or a space described by an ICC profile, written here as 8-bit sRGB.
Transparency: the ICO stores it as 8-bit alpha in 32-bit and PNG entries, or a 1-bit mask in old icons; the JP2 keeps it as an extra component flagged as opacity.
Other images: the ICO can hold several sizes of the same picture, typically 16, 32, 48 and 256 px; only the main image is converted.
Metadata: the ICO can carry only a directory of the sizes inside, with no EXIF; JP2 can carry XML, ICC and resolution boxes, but nothing is copied across.
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.
ICO files usually come from website favicons, Windows programs and installers.
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.
When converting ICO to JP2 makes sense
JP2 is the better choice for archival masters and specialist imaging, while ICO suits favicons and Windows icons.
JP2 strengths: True lossless mode; High bit depths and very large images; Standardised for archives and digital cinema. Drawbacks to weigh: Browsers do not display it; Slow to encode and decode; Patchy support in everyday apps.
Limitations
- The largest image in the icon is the one converted; smaller sizes that were hand-tuned for 16 px are not carried over.
- Lossless JPEG 2000 is larger than a lossy one, but usually smaller than an uncompressed TIFF of the same pixels.
- No current browser displays JP2 by default; archive and imaging software opens it.
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Frequently asked questions
Does converting ICO to JP2 lose quality?
JP2 is written losslessly, so the pixels are stored exactly as decoded. Not carried over: any several sizes of the same picture.
Is transparency kept in the JP2?
Yes. ICO stores it as 8-bit alpha in 32-bit and PNG entries, or a 1-bit mask in old icons, and the JP2 is written with an alpha channel, so transparent areas stay transparent.
Is the JPEG 2000 file lossless?
Yes. It is written with JPEG 2000's reversible 5/3 wavelet, so decoding it gives back exactly the pixels that went in. The trade-off is size: a lossless JP2 is larger than a lossy one, though usually smaller than an uncompressed TIFF.
Which apps open JP2 files?
MacOS Preview, GIMP, IrfanView, XnView, ImageMagick and the OpenJPEG tools. It does not open in web browsers by default.
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.