HDR vs ICO
A detailed comparison of Radiance HDR Image and ICO Icon — file size, quality, compatibility, and which format to choose for your workflow.
Technical Specifications
| 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+) |
Strengths Comparison
.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.
.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
.HDR — 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.
- Aging — OpenEXR is the modern professional choice.
.ICO — 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).
- Editing requires specialized tools — most image editors treat it as a curiosity.
Frequently Asked Questions
HDR (Radiance HDR Image) is an image format used to store raster graphics — a two-dimensional grid of pixels describing a picture. It is part of the raster & vector images family and designed around a specific trade-off between file size, visual fidelity, and feature support (transparency, colour depth, compression type). Photographers, web designers, and content creators choose HDR when its particular strengths match the publishing target.
ICO (Icon) is Microsoft's 1985 multi-resolution icon format, originally shipped with Windows 1.0. A single .ico file holds multiple sizes (16×16, 32×32, 48×48, 256×256) so the OS can pick the best one for the current display context. Since 1999, every website uses a favicon.ico to show its icon in browser tabs.
Most desktop photo viewers (Windows Photos, macOS Preview, GIMP, Photoshop, Affinity Photo) open HDR natively. On mobile, iOS Photos and Google Photos display HDR in the gallery when supported by the OS. If the format is rare or new, convert to JPG or PNG first — both are universally readable — using our HDR to JPG or HDR to PNG converter.
On Windows, ICO files open natively in File Explorer and Photos. On macOS, Preview handles basic display. For editing, use GIMP (free), Photoshop with a plugin, or dedicated icon editors like IcoFX.
Upload the HDR to KaijuConverter and pick a target format (JPG, PNG, WebP, HEIC, TIFF, BMP, SVG, PDF). The conversion runs in the browser via ImageMagick and returns a download in seconds. No account or installation required; both input and output delete automatically within two hours.
It depends on the task. JPG is the smallest file size for photographs; PNG is lossless with transparency; HDR has its own niche that may favour colour depth, animation, or encoding efficiency over one or both of those. For the final web publish, test all three and measure file size plus visible quality on real content.
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