BMP to HDR Converter
Convert BMP to HDR in your browser. BMP files usually come from Windows Paint, legacy Windows programs, embedded displays and some scanners; 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
BMP expected · other image formats also work
How to use BMP to HDR
- 1
Add your BMP 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 bmp to hdr
Where the HDR goes next
HDR opens in Blender, Photoshop, Houdini, Unreal Engine, Unity and Affinity Photo.
HDR next to BMP
Both sides are lossless, so the size depends on how well the HDR encoder handles this picture compared with the BMP's usually none; RLE for some 4 and 8-bit files.
Written without a lossy pass
The HDR is written losslessly, so the pixels decoded from the BMP 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.
BMP vs HDR
What changes from BMP to HDR
Encoding: the BMP uses usually none; RLE for some 4 and 8-bit files; 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, 4, 8, 16, 24 or 32 bits per pixel in the BMP; 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 an indexed palette in the BMP; HDR supports linear RGB (or XYZ in the XYZE variant), written here as linear-light RGB.
Transparency: the BMP stores it as an optional fourth byte in 32-bit files, which many programs ignore; the HDR has none, so transparent areas are filled with the colour you choose.
Metadata: the BMP can carry nothing beyond the header's resolution fields (and a colour profile in rare V5 headers); HDR can carry a text header with FORMAT, EXPOSURE and optional comments, but nothing is copied across.
About BMP
BMP stores raw, uncompressed pixels. Files are huge but trivially simple, which is why some legacy Windows software, embedded displays and printers still ask for it.
A BMP is a 14-byte file header ('BM' and the offset to the pixels), a DIB header (40 bytes, or 108 and 124 bytes in the V4 and V5 versions that add colour masks and alpha), an optional palette, then pixel rows padded to 4 bytes and normally stored bottom-up.
BMP files usually come from Windows Paint, legacy Windows programs, embedded displays and some scanners.
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 BMP to HDR makes sense
HDR is the better choice for 3D lighting and environment maps, while BMP suits legacy software and embedded systems that require it.
HDR strengths: True high dynamic range; Standard for HDRI environment maps. Drawbacks to weigh: Needs tone mapping to view on normal screens.
Limitations
- BMP stores nearly every pixel literally, so almost any compressed target is several times smaller.
- A 32-bit BMP can carry an alpha byte that most programs ignore; if the image suddenly gains transparent areas after converting, that byte was set.
- 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 BMP to HDR lose quality?
HDR is written losslessly, so the pixels are stored exactly as decoded.
What happens to transparency when converting BMP to HDR?
BMP stores transparency as an optional fourth byte in 32-bit files, which many programs ignore. 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.