Radiance

Radiance pictures hold three 8-bit mantissas and a shared exponent per pixel (RGBE), or CIE X, Y and Z the same way (XYZE). RadianceFormat reads both, every scan order a resolution line can name (-Y 512 +X 768 and the other seven), and flat, old-style repeat-pixel and per-channel run-length scanlines. Pixels load as RgbF32, bit for bit what stb_image decodes; XYZE converts to RGB in Radiance's standard primaries, which RasterMetadata.Primaries then names. A PRIMARIES line sets the primaries of an RGBE file the same way; without one, Rec. 709 is assumed.

RadianceDetails keeps the header: the RadiancePixelFormat, Exposure, ColorCorrection, Primaries, Software, View, PixelAspectRatio, the scan order as stored and every header line. The reader also measures the brightest value and stores it as HdrMetadata.MaxContentLightLevel, so ToneMap fits the image rather than a fixed 1,000 cd/m² peak.

// Linear light, unclamped: 1.0 is reference white. The brightest value is measured as the light level ToneMap fits.
using Raster<RgbF32> hdr = Raster.Load<RgbF32>("desk.hdr");
var details = (RadianceDetails)hdr.Metadata.FormatDetails!;
double? exposure = details.Exposure;                    // the header's EXPOSURE lines; the pixels are kept as stored

// To SDR: tone map, then save. Saving the HDR raster to PNG or JPEG as it is would clip the highlights.
using Raster<RgbF32> mapped = hdr.Derive(ops => ops.ToneMap(ToneMapping.Bt2390));
mapped.Save("desk.jpg");

// RGBE with per-channel run-length scanlines, as Radiance writes them; EXPOSURE only when asked for.
hdr.Save("copy.hdr");
hdr.Save("labeled.hdr", new RadianceWriterOptions { Exposure = 1.5 });

The writer writes RGBE, top row first, with per-channel run-length scanlines (RadianceWriterOptions.Compress = false writes them flat) and an EXPOSURE line only when RadianceWriterOptions.Exposure is set. Reading a file and writing it again gives the same floats, and the same bytes once written by Egami.

Pixels are linear light with 1.0 as reference white; the HDR guide explains the scale, and ToneMap in color management turns them into SDR.