Add support for OpenEXR image format by brianpopow · Pull Request #3096 · SixLabors/ImageSharp

brianpopow · 2026-03-29T18:12:31Z

Prerequisites

I have written a descriptive pull-request title
I have verified that there are no overlapping pull-requests open
I have verified that I am following the existing coding patterns and practice as demonstrated in the repository. These follow strict Stylecop rules 👮.
I have provided test coverage for my change (where applicable)

Description

This PR adds support for decoding and encoding of images in the OpenEXR format. OpenEXR is a HDR image format, therefore I have added two new pixel formats Rgb96 and Rgba128 which store each color channel as UInt32.

The specification can be found here: https://openexr.com/en/latest/index.html#openexr

A reference implementation can be found here: https://github.com/AcademySoftwareFoundation/openexr.git

# Conflicts: # src/ImageSharp/Configuration.cs

# Conflicts: # src/ImageSharp/Formats/Bmp/BmpConstants.cs # src/ImageSharp/Formats/Bmp/BmpDecoder.cs # src/ImageSharp/Formats/Bmp/BmpFormat.cs

# Conflicts: # src/ImageSharp/Configuration.cs # src/ImageSharp/Formats/Bmp/BmpArrayFileHeader.cs # src/ImageSharp/Formats/Bmp/BmpConstants.cs # src/ImageSharp/Formats/Bmp/BmpFormat.cs # src/ImageSharp/Formats/Bmp/BmpImageFormatDetector.cs # src/ImageSharp/Formats/ImageExtensions.Save.cs # src/ImageSharp/Formats/Pbm/BufferedReadStreamExtensions.cs # tests/ImageSharp.Tests/ConfigurationTests.cs # tests/ImageSharp.Tests/Formats/GeneralFormatTests.cs

# Conflicts: # src/ImageSharp/Configuration.cs # src/ImageSharp/Formats/Bmp/BmpArrayFileHeader.cs # src/ImageSharp/Formats/Bmp/BmpConstants.cs # src/ImageSharp/Formats/Bmp/BmpDecoder.cs # src/ImageSharp/Formats/Bmp/BmpDecoderCore.cs # src/ImageSharp/Formats/Bmp/BmpFileHeader.cs # src/ImageSharp/Formats/Bmp/BmpFormat.cs # src/ImageSharp/Formats/Bmp/BmpImageFormatDetector.cs # src/ImageSharp/Formats/Bmp/BmpInfoHeader.cs # src/ImageSharp/Formats/ImageDecoderUtilities.cs # src/ImageSharp/Formats/ImageExtensions.Save.cs # src/ImageSharp/Formats/Pbm/BufferedReadStreamExtensions.cs # src/ImageSharp/Image.Decode.cs # tests/ImageSharp.Tests/ConfigurationTests.cs # tests/ImageSharp.Tests/Formats/GeneralFormatTests.cs

# Conflicts: # src/ImageSharp/Formats/Bmp/BmpFormat.cs # src/ImageSharp/Formats/ImageDecoderUtilities.cs # src/ImageSharp/Formats/ImageExtensions.Save.cs # src/ImageSharp/Formats/OpenExr/ExrDecoderCore.cs

# Conflicts: # src/ImageSharp/Configuration.cs # src/ImageSharp/Formats/ImageDecoderUtilities.cs # tests/ImageSharp.Tests/TestUtilities/TestEnvironment.Formats.cs

src/ImageSharp/Formats/Exr/ExrDecoderCore.cs

src/ImageSharp/Formats/Exr/ExrEncoderCore.cs

src/ImageSharp/Formats/Exr/ExrDecoderCore.cs

src/ImageSharp/Formats/Exr/ExrEncoderCore.cs

src/ImageSharp/Formats/Exr/ExrDecoderCore.cs

src/ImageSharp/Formats/Exr/ExrEncoderCore.cs

src/ImageSharp/Formats/Exr/Compression/Decompressors/B44ExrCompression.cs

JimBobSquarePants · 2026-03-31T03:44:22Z

@brianpopow I'll review this asap.

antonfirsov · 2026-03-31T11:05:07Z

src/ImageSharp/Common/Helpers/ColorNumerics.cs

+    /// <param name="component">The 32 bit component value.</param>
+    /// <returns>The <see cref="byte"/> value.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static byte From32BitTo8Bit(uint component) => (byte)(component * Scale32Bit);


Perf is maybe not a primary concern at this point but I wonder if there is a cheaper way to correctly calculate this that avoids FP conversion? How does the reference implementation calculate this (if they care about decoding into lower res format)?

@brianpopow actually, I don't understand this. From32BitTo8Bit(uint.MaxValue) == 1. Are you sure this logic is correct? If it's incorrect, I wonder why tests didn't catch it? Wouldn't (byte)(component >> 16) do the job?

@antonfirsov Yes I think you are right, this does not look right.

I wonder why tests didn't catch it?

There are no pixel conversion tests yet for the new pixel types. I will try to add tests for the new pixlel types Rgb96 and Rgba128 next.

Wouldn't (byte)(component >> 16) do the job?

Yeah that's more like it, but I think it should be (byte)(component >> 24)? Lets say we have for example Int.Max / 2, e.g. 2147483647. Converting this to 8 bit should be 127.

src/ImageSharp/IO/BufferedReadStream.cs

antonfirsov

Couple of places where the return value from stream.Read(...) is not checked. I may have missed some, it is worth a comprehensive check.

src/ImageSharp/Formats/Exr/Compression/Decompressors/NoneExrCompression.cs

src/ImageSharp/Formats/Exr/ExrDecoderCore.cs

JimBobSquarePants · 2026-04-06T13:24:38Z

@brianpopow I'll be able to focus on a proper review this week.

JimBobSquarePants · 2026-04-06T13:26:40Z

src/ImageSharp/Formats/Exr/Compression/Compressors/NoneExrCompressor.cs

+    }
+
+    /// <inheritdoc/>
+    public override ExrCompression Method => ExrCompression.Zip;


Is this correct?

JimBobSquarePants · 2026-04-06T13:28:27Z

src/ImageSharp/PixelFormats/PixelImplementations/Rgba128.cs

+/// </para>
+/// </summary>
+[StructLayout(LayoutKind.Sequential)]
+public partial struct Rgba128 : IPixel<Rgba128>, IEquatable<Rgba128>


Doesn't this mean our processes are all actually lossy?

JimBobSquarePants · 2026-04-06T13:28:59Z

src/ImageSharp/PixelFormats/PixelImplementations/Rgba128.cs

+            PixelAlphaRepresentation.Unassociated);
+
+    /// <inheritdoc/>
+    public readonly Rgba32 ToRgba32() => throw new NotImplementedException();


We need to implement all these.

JimBobSquarePants · 2026-04-06T13:31:53Z

tests/Directory.Build.targets

    See https://github.com/ImageMagick/ImageMagick/commit/27a0a9c37f18af9c8d823a3ea076f600843b553c
    -->
-    <PackageReference Update="Magick.NET-Q16-AnyCPU" Version="13.10.0" />
+    <PackageReference Update="Magick.NET-Q16-AnyCPU" Version="14.11.1" />


Oh, you got this working!! Fantastic!! 🙌

I had to upgrade to the latest version of Magick.NET, because of an issue decoding some exr files, which was fixed here

Unfortunately this also changed how some bitmaps which are RLE compressed are decoded. I had to change some testcases to use CompareToReferenceOutput instead of using the reference decoder: 0c3ca3d

JimBobSquarePants · 2026-04-06T13:33:07Z

src/ImageSharp/Formats/Exr/Compression/Compressors/ZipExrCompressor.cs

+        for (int i = 1; i < predicted.Length; i++)
+        {
+            int d = (predicted[i] - p + 128 + 256) & 255;
+            p = predicted[i];


You can use ref here

JimBobSquarePants · 2026-04-06T13:34:09Z

src/ImageSharp/Formats/Exr/Compression/Decompressors/ZipExrCompression.cs

+
+        if (totalRead == 0)
+        {
+            ExrThrowHelper.ThrowInvalidImageContentException("Could not read zip compressed image data!");


I wonder if we should just break here? Normally we try to return as much pixel information as we can.

JimBobSquarePants · 2026-04-06T13:36:19Z

src/ImageSharp/Formats/Exr/Compression/ExrBaseDecompressor.cs

+
+namespace SixLabors.ImageSharp.Formats.Exr.Compression;
+
+internal abstract class ExrBaseDecompressor : ExrBaseCompression


I know these types are internal but I'm finding it very useful currently to document the crap out of everything (AI really helps here.)

brianpopow · 2026-04-07T09:20:08Z

@brianpopow I'll be able to focus on a proper review this week.

@JimBobSquarePants: dont worry keep your time, it is not urgent.

Just as a heads up: I noticed issues with the pixel conversion methods introduced with the new pixel types. I am trying to add tests for them in the next days. Those conversion methods will change, so maybe exclude them from a review until then, because they will change anyway.

tests/ImageSharp.Tests/PixelFormats/Rgb96Tests.cs

+
+        PixelComponentInfo? maybeComponentInfo = info.ComponentInfo;
+        Assert.NotNull(maybeComponentInfo);
+        PixelComponentInfo componentInfo = maybeComponentInfo.Value;


brianpopow added 30 commits December 26, 2021 11:24

Parse open EXR header

9dda678

Decode uncompressed EXR images with 16 bit pixel data for each channel

a27696a

Decode EXR images with 32 bit float pixel data

d3993f7

Decode EXR images with unsigned int pixel data

aaf2143

Encode EXR image with float pixel data

799dafe

Encode EXR image with HalfSingle pixel data

4cf95a5

Encode EXR image with usigned int pixel data

7e7472d

Update tests for EXR images

652b385

Add support for decoding EXR images with alpha channel

70cfcc9

Add support for decoding exr with zips compression

3279762

Add support for decoding RLE exr images

85501f3

Add support for ZIP compressed exr images

69c8cd8

Add support for decoding gray exr images

fdc7b61

Refactor

fd0c245

Merge remote-tracking branch 'origin/main' into bp/openExr

88a06e8

# Conflicts: # src/ImageSharp/Configuration.cs

Merge remote-tracking branch 'origin/main' into bp/openExr

aabe561

# Conflicts: # src/ImageSharp/Formats/Bmp/BmpConstants.cs # src/ImageSharp/Formats/Bmp/BmpDecoder.cs # src/ImageSharp/Formats/Bmp/BmpFormat.cs

Fix build errors

ea1aaa7

Add exr decoder tests

ce21f1a

Add support for decoding b44 compressed exr files

a9620ee

Fix warnings

ec8163a

Add DecodeTiledFloatingPointPixelData

28dcdf2

Merge remote-tracking branch 'origin/bp/openExr' into bp/openExr

d0d5e86

# Conflicts: # src/ImageSharp/Formats/Bmp/BmpFormat.cs # src/ImageSharp/Formats/ImageDecoderUtilities.cs # src/ImageSharp/Formats/ImageExtensions.Save.cs # src/ImageSharp/Formats/OpenExr/ExrDecoderCore.cs

Merge branch 'main' into bp/openExr

7748467

# Conflicts: # src/ImageSharp/Configuration.cs # src/ImageSharp/Formats/ImageDecoderUtilities.cs # tests/ImageSharp.Tests/TestUtilities/TestEnvironment.Formats.cs

Adjust exr decoder / encoder to ImageSharp changes

fa52ab7

Change exr name space to SixLabors.ImageSharp.Formats.Exr

83dba58

Fix issue in ExrImageFormatDetector.cs returning wrong format

b78402d

Use MagickReference decoder for exr decoding tests

faf87fb

Fix issue assigning pixel value from HalfVector4

eaea042

github-code-quality bot found potential problems Mar 29, 2026

View reviewed changes

brianpopow added 3 commits March 30, 2026 10:39

Fix failing bmp tests

0c3ca3d

Change expectedDefaultConfigurationCount to 12

e6a9980

Use CompareToReferenceOutput for failing bmp tests on linux

802e275

github-code-quality bot found potential problems Mar 30, 2026

View reviewed changes

src/ImageSharp/Formats/Exr/ExrDecoderCore.cs Fixed Show fixed Hide fixed

src/ImageSharp/Formats/Exr/ExrDecoderCore.cs Fixed Show fixed Hide fixed

Remove unused variables

fccd5b5

github-code-quality bot found potential problems Mar 30, 2026

View reviewed changes

Remove more unused variables

84182c5

antonfirsov reviewed Mar 31, 2026

View reviewed changes

brianpopow and others added 3 commits April 1, 2026 12:46

Move ReadSingle() to ExrDecoderCore

0aeaaf7

Evaluate return value of stream.Read() to make sure enough data was read

1853289

Merge branch 'main' into bp/openExr

2916204

JimBobSquarePants reviewed Apr 6, 2026

View reviewed changes

Merge branch 'main' into bp/openExr

05c89f7

brianpopow and others added 3 commits April 7, 2026 18:03

Add tests for Rgb96 pixel conversions

d1623fe

Try fix issues with Rgb96 pixel conversions

787ebb2

Merge branch 'main' into bp/openExr

3fbf0ef

github-code-quality bot found potential problems Apr 7, 2026

View reviewed changes

tests/ImageSharp.Tests/PixelFormats/Rgb96Tests.cs Fixed Show fixed Hide fixed

Add null check for PixelComponentInfo in Rgb96_PixelInformation()

0ec523f

github-code-quality bot found potential problems Apr 7, 2026

View reviewed changes

tests/ImageSharp.Tests/PixelFormats/Rgb96Tests.cs

PixelComponentInfo? maybeComponentInfo = info.ComponentInfo;

Assert.NotNull(maybeComponentInfo);

PixelComponentInfo componentInfo = maybeComponentInfo.Value;


		namespace SixLabors.ImageSharp.Formats.Exr.Compression;

		internal abstract class ExrBaseDecompressor : ExrBaseCompression

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JimBobSquarePants commented Mar 31, 2026

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JimBobSquarePants commented Apr 6, 2026

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brianpopow commented Apr 7, 2026

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