Free online JP2 to ICO converter

Windows applications, desktop shortcuts, folders, and some favicon workflows require an ICO file rather than a JP2 image. Converting the source creates a Windows icon container that can hold several raster sizes for different display contexts.

What the JP2 format is

JP2 is the JPEG 2000 file format, based on wavelet compression rather than the discrete cosine transform used by ordinary JPEG. It supports lossy and lossless compression, different component bit depths, and an optional alpha channel.

JP2 is used by scanners, digital archives, GIS and medical-imaging systems, and applications built around JPEG 2000 codecs. ImageMagick, GIMP, Adobe Photoshop with suitable support, and specialist imaging software can open or create JP2 files, but browser and operating-system support is less consistent than for PNG or JPEG.

What the ICO format is

ICO is the Windows icon container format. One file can store multiple raster images, commonly at 16×16, 32×32, 48×48, 64×64, 128×128, and 256×256 pixels, so Windows or an application can select a suitable size.

ICO is used for executable icons, shortcuts, folders, application resources, and legacy website favicons. It supports transparency through an alpha channel and can contain PNG-compressed image entries, but it is not a vector format. Each required size must therefore be rendered as a raster image.

Convert online without installing software

Use the free converter on 101convert.com: select the JP2 file, choose ICO as the output format, start the conversion, and download the resulting file. Check the output dimensions and transparency before assigning the icon to a shortcut, folder, application, or website.

Convert with ImageMagick

ImageMagick is suitable for command-line and batch conversion. Install a build with JPEG 2000 support, then run:

magick input.jp2 -background none -alpha on -define icon:auto-resize=256,128,64,48,32,16 output.ico

This creates an ICO containing several standard sizes. -background none prevents transparent areas from being filled with a solid color, while -alpha on enables the alpha channel; neither option can create transparency that is absent from the JP2.

For one square 256-pixel icon, crop or pad the image to a square while preserving its aspect ratio:

magick input.jp2 -resize 256x256^ -gravity center -extent 256x256 -background none -alpha on output.ico

Inspect the generated entries with:

magick identify output.ico

If ImageMagick reports that JP2 is unsupported, the installed build lacks a JPEG 2000 delegate such as OpenJPEG support. Install a build with that delegate, or open the JP2 in GIMP and export it as PNG before converting the PNG to ICO.

Convert with a desktop editor

Open the JP2 in GIMP or another editor that supports both JPEG 2000 and ICO export. Crop or pad the image to a square canvas, resize it for the required icon sizes, retain the alpha channel if needed, and use File → Export As to save an .ico file. If the exporter accepts only one image size, create separate 16, 32, 48, and 256-pixel images and package them with an icon-authoring tool.

Quality and compatibility limits

Conversion does not restore detail lost through JP2 compression or produce detail absent from a small source. Enlarging a low-resolution image to 256×256 can make it blurry. A rectangular source must be cropped or padded; stretching it into a square distorts the image.

Use a lossless JP2 source for sharp text, logos, and line art. Include multiple sizes when the icon will be displayed at different resolutions, and test the ICO in the exact Windows application or embedded system that will load it. Some older software accepts only particular dimensions or older bitmap encoding, despite modern ICO files supporting PNG-compressed entries.

ICO is intended for small icons, not general-purpose photographs. If the receiving program accepts PNG and does not specifically require an icon container, PNG is usually the more suitable output.