CONVERT
HDR → ICO
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Fast, secure HDR to ICO conversion. No registration required.
Here is the short version — HDR is a raster image format with its own balance of compression, colour depth, and software support. Hence the need for ICO. If you have ended up with a HDR and need a ICO, the mismatch is almost always about where the image is going next rather than the picture itself. Our server reads the HDR with ImageMagick, decodes each pixel, and re-writes it as a ICO using defaults tuned for fidelity first and file size second. In practice HDR is a raster image format with its own balance of compression, colour depth, and software support. On the other end, ICO is the Windows icon container with multiple resolutions packed into one file.
Radiance HDR Image
Source formatHDR (Radiance) stores high dynamic range images for realistic lighting in 3D rendering.
ICO Icon
Target formatICO is the icon file format used for favicons and Windows application icons. A single ICO file can contain multiple image sizes and color depths for different display contexts.
Why convert HDR to ICO
Both HDR and ICO describe a grid of pixels — the difference lies in how that grid is compressed, whether transparency is supported, and which software opens it natively. Moving from HDR to ICO is worth it when the ICO ecosystem is broader for your use case, or when ICO compresses photographs more efficiently than HDR.
HOW TO CONVERT
HDR → ICO
Drop the HDR file
Drag and drop or click to upload your HDR. The image is transferred securely over HTTPS and queued for conversion.
Re-encode with ImageMagick
ImageMagick decodes every pixel of the HDR and writes a matching ICO with sensible default quality settings.
Download the ICO
The converted ICO is ready to download as a single file; both files delete automatically within two hours.
Common Use Cases
Share across platforms
Send ICO files to anyone without worrying about whether they have the right software for HDR.
Embed in documents
Drop ICO output into Word, Google Docs, PowerPoint, Notion or a website without conversion warnings.
Optimize size
ICO often produces smaller files than HDR for web, email and storage.
Archive & future-proof
Store in a widely-supported format that will still open on future operating systems without legacy plugins.
HDR vs ICO — Strengths and limitations
What each format does best, and where it falls short.
HDR Strengths
- True floating-point dynamic range in 32 bits per pixel.
- Simple format — easy to parse and generate.
- Standard for environment maps and lighting probes in 3D.
- 30+ years of continuous use in architectural rendering.
Limitations
- No compression — files are larger than OpenEXR or AVIF for equivalent quality.
- Only one channel set (RGB) — no alpha, no multi-layer like EXR.
- Not a web format.
ICO Strengths
- Multi-resolution: one file, many sizes, OS picks the right one.
- Universal favicon support in every browser since IE5.
- Supports transparency (1-bit since 1985, full alpha since XP).
- Tiny file size — an entire favicon pack typically fits in under 15 KB.
- No licensing or patent concerns — fully in the public domain spec-wise.
Limitations
- Cannot compress continuous-tone images efficiently — use PNG or WebP for photos.
- Format is essentially frozen in 1999 — no HDR, no wide gamut, no modern features.
- Maximum image dimension is 256×256 px (inside an ICO container).
HDR vs ICO — Technical specifications
Side-by-side comparison of the technical details.
HDR
- MIME type
- image/vnd.radiance
- Extensions
- .hdr, .pic
- Encoding
- RGBE (shared 8-bit exponent)
- Dynamic range
- ~76 orders of magnitude
- Creator
- Greg Ward, Radiance renderer (1991)
ICO
- MIME type
- image/vnd.microsoft.icon
- Max resolutions per file
- 65 535 images
- Max single image size
- 256×256 px
- Color depths
- 1, 4, 8, 24, 32 bits per pixel
- Compression
- Uncompressed bitmap or embedded PNG (Vista+)
| Specification | HDR | ICO |
|---|---|---|
| MIME type | image/vnd.radiance | image/vnd.microsoft.icon |
| Extensions | .hdr, .pic | — |
| Encoding | RGBE (shared 8-bit exponent) | — |
| Dynamic range | ~76 orders of magnitude | — |
| Creator | Greg Ward, Radiance renderer (1991) | — |
| Max resolutions per file | — | 65 535 images |
| Max single image size | — | 256×256 px |
| Color depths | — | 1, 4, 8, 24, 32 bits per pixel |
| Compression | — | Uncompressed bitmap or embedded PNG (Vista+) |
HDR vs ICO — Typical file sizes
Approximate file sizes for common scenarios.
HDR
- 2K environment map 15-35 MB
- 4K environment map 60-130 MB
- 8K HDRI 250-500 MB
ICO
- Classic favicon (16×16 only) < 2 KB
- Multi-size favicon pack (16/32/48/256) 5-15 KB
- Full Windows app icon set 20-100 KB
Quality & Compatibility
If ICO is a lossless format (PNG, TIFF, BMP) the output keeps every pixel of the decoded HDR exactly. If ICO is a lossy codec (JPEG, WebP, HEIC), the encoder re-compresses the image at the quality level you select — default 85 is transparent for photographs, quality 92+ for illustrations with hard edges.
Tips for Best Results
- Keep the original HDR alongside the ICO output — re-encoding already-lossy images accumulates detail loss on each round.
- If the ICO will be uploaded to a CMS, check whether the platform has a max dimension and downscale once on export rather than letting the CMS resize automatically.
- For thumbnails and avatars, export the ICO at exactly the display size; browsers will otherwise resample and the image may look soft.
Frequently Asked Questions
It depends on the codecs involved. If both HDR and ICO are lossy, the pixels are re-encoded and a small amount of detail is discarded — invisible at default quality settings on photographs. If ICO is lossless (PNG, TIFF, BMP) the output keeps every pixel of the decoded HDR exactly, but cannot recover detail that HDR had already compressed away.
Often yes, especially when ICO is lossless. HDR tuned for efficient web delivery will usually produce smaller files than ICO's default settings. If file size matters, drop the quality in Advanced or pick a more compressed target format instead.
KaijuConverter uploads over HTTPS, processes the image in an isolated container and deletes both the source and the output within two hours. No account is required, file contents are never logged, and we do not use uploads to train any model. For confidential material, the paid plan includes a data-processing agreement.
Related comparisons
See these formats side by side to understand which fits your use case best.
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Read guideSecure & Private Conversion
Your files are encrypted during transfer, processed in isolated containers, and automatically deleted within 60 minutes. We never read, share, or store your data.