HDR to BMP Converter

Encoding: the HDR uses run-length encoded RGBE scanlines; BMP uses usually none; RLE for some 4 and 8-bit files, and the download is an uncompressed 24-bit BMP, or 32-bit with alpha when the image has transparency.

Bit depth: an 8-bit mantissa per channel sharing an 8-bit exponent (RGBE), 32 bits per pixel in the HDR; BMP allows 1, 4, 8, 16, 24 or 32 bits per pixel, and the BMP written here has 24 or 32 bits per pixel. The high dynamic range is mapped to 8 bits per channel, and values above white clip.

Colour: linear RGB (or XYZ in the XYZE variant) in the HDR; BMP supports RGB or an indexed palette, written here as 8-bit sRGB.

Metadata: the HDR can carry a text header with FORMAT, EXPOSURE and optional comments; BMP can carry nothing beyond the header's resolution fields (and a colour profile in rare V5 headers), but nothing is copied across.

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.

HDR files usually come from HDRI environment maps, 360° panoramas and lighting simulation.

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 is the better choice for legacy software and embedded systems that require it, while HDR suits 3D lighting and environment maps.

BMP strengths: No compression artifacts; Read by very old and very simple software. Drawbacks to weigh: Enormous files; Poor support for transparency; No metadata.