HDR to ICO Converter
Convert HDR to ICO in your browser. HDR files usually come from HDRI environment maps, 360° panoramas and lighting simulation; 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
HDR expected · other image formats also work
How to use HDR to ICO
- 1
Add your HDR 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 hdr to ico
Where the ICO goes next
ICO opens in every browser (as a favicon), Windows and most Linux desktops.
ICO next to HDR
Both sides are lossless, so the size depends on how well the ICO encoder handles this picture compared with the HDR's run-length encoded RGBE scanlines.
Written without a lossy pass
The ICO is written losslessly, so the pixels decoded from the HDR 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.
HDR vs ICO
What changes from HDR to ICO
Encoding: the HDR uses run-length encoded RGBE scanlines; 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: an 8-bit mantissa per channel sharing an 8-bit exponent (RGBE), 32 bits per pixel in the HDR; ICO allows 1 to 32 bits per pixel, set per size, and the ICO written here has 32 bits per pixel. The high dynamic range is mapped to 8 bits per channel, and values above white clip.
Colour: linear RGB (or XYZ in the XYZE variant) in the HDR; ICO supports RGB or a palette, per image, written here as 8-bit sRGB.
Metadata: the HDR can carry a text header with FORMAT, EXPOSURE and optional comments; ICO can carry only a directory of the sizes inside, with no EXIF, but nothing is copied across.
About HDR
Radiance .hdr stores high dynamic range light values, widely used for 3D environment maps and HDRI lighting.
A Radiance file starts with '#?RADIANCE' (or '#?RGBE'), text lines such as FORMAT=32-bit_rle_rgbe and EXPOSURE, a blank line, a resolution line like '-Y 2048 +X 4096', then the scanlines.
HDR files usually come from HDRI environment maps, 360° panoramas and lighting simulation.
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 HDR to ICO makes sense
ICO is the better choice for favicons and Windows icons, while HDR suits 3D lighting and environment maps.
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
- Light values above 1.0 are clipped rather than tone-mapped, so the sun and bright sky turn flat white.
- Environment maps are 2:1 equirectangular panoramas, so the picture looks stretched near the top and bottom, as it should.
- Files in the XYZE variant cannot be read here; RGBE files, the common kind, can.
- 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 HDR to ICO lose quality?
ICO is written losslessly, so the pixels are stored exactly as decoded. The high dynamic range is mapped to 8 bits per channel, and values above white clip.
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.