ICO to HDR Converter
Convert ICO to HDR in your browser. ICO files usually come from website favicons, Windows programs and installers; HDR is the better fit for 3D lighting and environment maps. You get a Radiance RGBE (.hdr) file, with the 8-bit sRGB values converted to linear light. 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 HDR
- 1
Add your ICO files: drop them here, choose them, or paste from the clipboard.
- 2
Pick the colour that replaces transparent areas, since HDR has none.
- 3
Click Convert. Each file is decoded and encoded in a background thread on this device.
- 4
Download the .hdr files one at a time or together as a ZIP.
Why use Aback Images for ico to hdr
Where the HDR goes next
HDR opens in Blender, Photoshop, Houdini, Unreal Engine, Unity and Affinity Photo.
HDR next to ICO
Both sides are lossless, so the size depends on how well the HDR 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 HDR 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 HDR
What changes from ICO to HDR
Encoding: the ICO uses each size stored as a headerless BMP or as a complete PNG; HDR uses run-length encoded RGBE scanlines, and the download is a Radiance RGBE (.hdr) file, with the 8-bit sRGB values converted to linear light.
Bit depth: 1 to 32 bits per pixel, set per size in the ICO; HDR allows an 8-bit mantissa per channel sharing an 8-bit exponent (RGBE), 32 bits per pixel, and the HDR written here has RGBE, 32 bits per pixel.
Colour: RGB or a palette, per image in the ICO; HDR supports linear RGB (or XYZ in the XYZE variant), written here as linear-light RGB.
Transparency: the ICO stores it as 8-bit alpha in 32-bit and PNG entries, or a 1-bit mask in old icons; the HDR has none, so transparent areas are filled with the colour you choose.
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; HDR can carry a text header with FORMAT, EXPOSURE and optional comments, 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 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.
When converting ICO to HDR makes sense
HDR is the better choice for 3D lighting and environment maps, while ICO suits favicons and Windows icons.
HDR strengths: True high dynamic range; Standard for HDRI environment maps. Drawbacks to weigh: Needs tone mapping to view on normal screens.
Limitations
- The largest image in the icon is the one converted; smaller sizes that were hand-tuned for 16 px are not carried over.
- No range is added: the HDR holds the 8-bit picture in linear light, and nothing in it is brighter than the original white.
- 3D software treats the file as linear light, so an ordinary photo used as an environment map may need its exposure raised to light a scene well.
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Frequently asked questions
Does converting ICO to HDR lose quality?
HDR is written losslessly, so the pixels are stored exactly as decoded. Not carried over: any several sizes of the same picture.
What happens to transparency when converting ICO to HDR?
ICO stores transparency as 8-bit alpha in 32-bit and PNG entries, or a 1-bit mask in old icons. HDR has no alpha channel, so transparent pixels are composited onto a solid colour, white unless you pick another. To keep transparency, convert to PNG, WebP or AVIF instead.
Does saving as HDR make a real HDRI?
No. A real HDRI is merged from several exposures. This file holds an 8-bit image in linear light, so 3D software reads it correctly, but it has no more range than the source.
Which apps open HDR files?
Blender, Photoshop, Houdini, Unreal Engine, Unity and Affinity Photo. It does not open in web browsers.
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.