About HDR Files
Radiance HDR Image
HDR (Radiance) stores high dynamic range images for realistic lighting in 3D rendering.
Family
Raster & Vector Images
Extension
.hdr
MIME Type
image/vnd.radiance
Can Use As
48 44 52 46 00 01 00 00 4B 41 49 4A
ASCII: HDRF....KAIJ
📈 Target Minimum File Size (Guaranteed ≥ KB)
Lossless JPEG Q100 + standard COM segment padding for government & exam portals
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HOW HDR CAME TO BE.
The .hdr extension was introduced by Greg Ward in 1991 for his Radiance renderer at Lawrence Berkeley Lab — one of the first physically-based global-illumination renderers for architectural lighting simulation. Radiance needed images that could represent real-world luminance, not just 0-255 per channel. Ward invented the RGBE encoding: three 8-bit channels for color plus a shared 8-bit exponent, giving a floating-point range from 10⁻³⁸ to 10³⁸ in only 32 bits per pixel.
Radiance HDR became the default high-dynamic-range texture format in 3D. Every environment map, every lighting probe, every "sunny HDRI" on Poly Haven, 3D asset marketplaces, and film studios is typically shipped as .hdr. OpenEXR later offered better compression and more channels, but .hdr’s RGBE remains the simplest path to a floating-point environment texture — a 40-year-old format still used daily in 3D.
Technical Specifications
- 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)
Typical Sizes & Weights
2K environment map
15-35 MB
4K environment map
60-130 MB
8K HDRI
250-500 MB
STRENGTHS & LIMITATIONS.
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.
- Aging — OpenEXR is the modern professional choice.
CURIOSITIES & TRIVIA.
Greg Ward invented RGBE encoding — shared exponent across RGB — to fit floating-point luminance in 32 bits per pixel.
Every "HDRI" environment map on sites like Poly Haven is a .hdr (or OpenEXR) file used for 3D lighting.
The format's dynamic range spans roughly 76 orders of magnitude — enough to represent both starlight and the sun in the same image.
Radiance, the renderer .hdr was built for, is still maintained in 2026 and used by architectural-lighting firms worldwide.
OpenEXR offers better compression, but .hdr wins on simplicity — 8 bytes per pixel, no compression library needed.
Specialized Utilities for .HDR Files
Compress Image to 20KB
Compress signature scans, stamp images, and ID photos to strictly ≤ 20 KB (20,000 bytes) for strict online exam and government application portals using binary-search JPEG quantization.
Compress Image to 50KB
Compress JPG, PNG, or WebP photos to strictly under 50 KB (50,000 bytes) for passport portals, university admissions, civil service forms, and KYC uploads without changing pixel dimensions.
Compress JPG to 100 KB
Upload a JPG and download a decodable JPG at or below 100,000 bytes. If the limit cannot be reached, no output is offered.
Crop Image & Photo Resizer
Crop and resize JPG, PNG, WEBP, and AVIF images to exact pixel dimensions, social media aspect ratios, or custom print DPI online for free.
Resize Image
Resize images to exact dimensions or scale by percentage. Lock aspect ratio to prevent distortion. Supports all common image formats.
PNG Compressor — Reduce PNG Size Preserving Transparency
Compress PNG images up to 80% while preserving full alpha-channel transparency, or lock exact file size targets (20 KB, 50 KB, 100 KB).
WEBP Compressor — Optimize WebP for Core Web Vitals
Compress WEBP images for ultra-fast page loads and Lighthouse scores with fine-grained quality sliders and exact byte targets.
Favicon Generator — Multi-Resolution .ICO from PNG, SVG or WEBP
Generate a production-ready multi-resolution favicon.ico containing 16x16, 32x32, 48x48, 64x64, 128x128, and 256x256 alpha layers from any logo.
EXIF Metadata Remover
Strip hidden GPS coordinates, camera serial numbers, timestamps, and XMP/IPTC metadata from JPG, PNG, WebP, and TIFF photos before sharing online.
Image to Text (OCR)
Extract text from images using optical character recognition. Supports photos of documents, screenshots, receipts, and handwritten notes in 100+ languages.
JPG to Word Converter (OCR)
Convert scanned JPG, PNG, and WEBP images into editable Microsoft Word (DOCX) documents using 12-language optical character recognition (OCR).
CONVERT FROM HDR
Common Use Cases
HDR photography, 3D rendering
Related Formats
Popular comparisons
HDR vs WEBP
Differences, file size, and when to choose each format.
HDR vs AVIF
Differences, file size, and when to choose each format.
HDR vs GIF
Differences, file size, and when to choose each format.
HDR vs BMP
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HDR vs TIFF
Differences, file size, and when to choose each format.
HDR vs ICO
Differences, file size, and when to choose each format.
Popular HDR conversions
The most-requested destinations when starting from HDR.
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.
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.
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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