Table of Contents

OpenEXR

ExrFormat reads scanline and tiled files, single and multi-part (ExrPartKind), with every compression of OpenEXR 3 (ExrCompression: NONE, RLE, ZIPS, ZIP, PIZ, PXR24, B44, B44A, DWAA and DWAB; HTJ2K is refused), half, float and uint channels (ExrPixelType), and luminance-chroma images. Pixels match OpenEXR's own decode bit for bit, DWA within one half-float step. A load gives the first part's R, G, B and A (or Y, YA or the luminance-chroma channels) as linear light; a tiled part loads its full-resolution level (ExrLevelMode says which levels it has). Deep parts throw UnsupportedFormatException.

ExrDetails lists every part as an ExrPart: its name, channels (ExrChannel), layers, data and display windows, tile size, chromaticities and every header attribute as an ExrHeaderEntry. ExrReaderOptions picks the Part, a Layer (such as diffuse for diffuse.R, diffuse.G and diffuse.B) and the ExrWindow to load: the data window, the pixels the file stores (the default), or the display window, padded with transparent black where there is no data. ExrImage.ReadChannel loads any one channel, such as depth or an object id, as 32-bit float.

// The first part's RGBA channels as linear light, 1.0 reference white; other layers by name.
using Raster<RgbaF32> beauty = Raster.Load<RgbaF32>("render.exr");
var details = (ExrDetails)beauty.Metadata.FormatDetails!;
IReadOnlyList<string> layers = details.Parts[details.Part].Layers;       // "diffuse", "specular"
using Raster<RgbaF32> diffuse = Raster.Load<RgbaF32>("render.exr", options: new ExrReaderOptions { Layer = "diffuse" });

// Any one channel, such as depth or an object id, as 32-bit float.
using Raster<GrayF32> depth = ExrImage.ReadChannel("aov.exr", "Z");

The writer writes one scanline part with R, G, B and A when the raster has alpha (ExrWriterOptions): ZIP by default, or NONE, RLE, ZIPS or PIZ, in half or float (ExrWriterOptions.PixelType; by default float for float rasters other than RgbaF16, half otherwise). A non-linear raster, such as sRGB, is converted to linear light first, and primaries other than Rec. 709 are written as chromaticities. OpenEXR reads every file Egami writes to the same values.

// Half-float RGBA, ZIP-compressed, by default; a sRGB or other non-linear raster is linearized first.
beauty.Save("copy.exr");
beauty.Save("float.exr", new ExrWriterOptions { Compression = ExrCompression.Piz, PixelType = ExrPixelType.Float });

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.

Recipes

A render pass from OpenEXR as JPEG

// One render pass of a multi-layer OpenEXR file, tone mapped for the web.
using Raster<RgbaF32> diffuse = Raster.Load<RgbaF32>("render.exr", options: new ExrReaderOptions { Layer = "diffuse" });
diffuse.Apply(ops => ops.ToneMap(ToneMapping.Bt2390));
diffuse.Save("diffuse.jpg", new JpegWriterOptions { Quality = 90 });

ExrReaderOptions.Layer picks a pass by name; ExrDetails lists the parts and layers a file has. ToneMap rolls off what is brighter than white instead of clipping it.

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