Imagesharp: Component shuffling for RGB(A)-like formats with SIMD Intrinsics

[antonfirsov]

We need cheap bulk-conversion between the following formats:
Argb32, Bgra32, Rgba32, Bgr24, Rgb24

We are especially interested in Rgb24, Bgr24 <=> Rgba32. I'm having sweat dreams about a community PR dealing with this problem. Should be easy for anyone having basic knowledge of System.Runtime.Intrinsics.

Implementation should be added to new span-based methods in PixelConverter.cs, those could be invoked than from T4 generated PixelOperations<TPixel> implementors like here:
https://github.com/SixLabors/ImageSharp/blob/78a584e8482b052d7a9885682299e2f37518d83d/src/ImageSharp/PixelFormats/PixelImplementations/Generated/Rgb24.PixelOperations.Generated.cs

If a PR would only add the PixelConverter helpers + tests, I'm happy to provide guidance or even finish the code for the rest of the work.

@john-h-k @Sergio0694 any chance you are interested?

Tasks:

• [x] Add 4=>4 channel shuffling methods to SimdUtils
• [x] Add 3=>4 channel shuffling methods to SimdUtils
• [x] Add 4=>3 channel shuffling methods to SimdUtils
• [x] Update Rgba32 compatible pixel operations to utilize new shuffle methods.
• [x] Update Rgb24 compatible pixel operations to utilize new shuffle methods.

[JimBobSquarePants]

I'm gonna have a look at this.

[antonfirsov]

Btw, the Span<Vector4> <=> Span<TPixel> conversions are delegating the (pad/slice) shuffle work to PixelOperations<TPixel> conversion methods:

https://github.com/SixLabors/ImageSharp/blob/78a584e8482b052d7a9885682299e2f37518d83d/src/ImageSharp/PixelFormats/Utils/Vector4Converters.RgbaCompatible.cs

Which means that the last two steps will be done automatically, if I'm not missing anything. Can't wait to see the Vector4 <=> Rgb24 before/after comparison. (Which is the main goal of this issue because of the conversion steps in Jpeg decoder and ResizeProcessor.)

[JimBobSquarePants]

@antonfirsov need to add a specific benchmark for that but I know for certain that even my Rgba32 <==> Rgb24 fallback is a lot faster than the original.

[JimBobSquarePants]

@antonfirsov Here you go!

ToVector4_Rgb24

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19041.572 (2004/?/20H1)
Intel Core i7-8650U CPU 1.90GHz (Kaby Lake R), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=3.1.403
  [Host]     : .NET Core 3.1.9 (CoreCLR 4.700.20.47201, CoreFX 4.700.20.47203), X64 RyuJIT
  Job-OIBEDX : .NET Framework 4.8 (4.8.4250.0), X64 RyuJIT
  Job-OPAORC : .NET Core 2.1.23 (CoreCLR 4.6.29321.03, CoreFX 4.6.29321.01), X64 RyuJIT
  Job-VPSIRL : .NET Core 3.1.9 (CoreCLR 4.700.20.47201, CoreFX 4.700.20.47203), X64 RyuJIT

IterationCount=3  LaunchCount=1  WarmupCount=3

Master

| Method | Job | Runtime | Count | Mean | Error | StdDev | Ratio | RatioSD | Gen 0 | Gen 1 | Gen 2 | Allocated |
|---------------------------- |----------- |-------------- |------ |-----------:|------------:|----------:|------:|--------:|-------:|------:|------:|----------:|
| PixelOperations_Base | Job-BPVKME | .NET 4.7.2 | 64 | 278.4 ns | 6.89 ns | 0.38 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-BPVKME | .NET 4.7.2 | 64 | 310.2 ns | 87.58 ns | 4.80 ns | 1.11 | 0.02 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-FBIBGB | .NET Core 2.1 | 64 | 231.9 ns | 254.31 ns | 13.94 ns | 1.00 | 0.00 | 0.0052 | - | - | 24 B |
| PixelOperations_Specialized | Job-FBIBGB | .NET Core 2.1 | 64 | 230.2 ns | 27.06 ns | 1.48 ns | 0.99 | 0.05 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-CETXPV | .NET Core 3.1 | 64 | 215.5 ns | 52.24 ns | 2.86 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-CETXPV | .NET Core 3.1 | 64 | 236.7 ns | 553.01 ns | 30.31 ns | 1.10 | 0.13 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-BPVKME | .NET 4.7.2 | 256 | 1,022.3 ns | 3,570.70 ns | 195.72 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-BPVKME | .NET 4.7.2 | 256 | 622.5 ns | 26.76 ns | 1.47 ns | 0.62 | 0.11 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-FBIBGB | .NET Core 2.1 | 256 | 762.3 ns | 103.78 ns | 5.69 ns | 1.00 | 0.00 | 0.0048 | - | - | 24 B |
| PixelOperations_Specialized | Job-FBIBGB | .NET Core 2.1 | 256 | 498.1 ns | 70.87 ns | 3.88 ns | 0.65 | 0.00 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-CETXPV | .NET Core 3.1 | 256 | 754.0 ns | 37.92 ns | 2.08 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-CETXPV | .NET Core 3.1 | 256 | 436.8 ns | 21.88 ns | 1.20 ns | 0.58 | 0.00 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-BPVKME | .NET 4.7.2 | 2048 | 5,679.3 ns | 1,454.37 ns | 79.72 ns | 1.00 | 0.00 | - | - | - | 24 B |
| PixelOperations_Specialized | Job-BPVKME | .NET 4.7.2 | 2048 | 3,460.6 ns | 273.43 ns | 14.99 ns | 0.61 | 0.01 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-FBIBGB | .NET Core 2.1 | 2048 | 6,033.8 ns | 8,785.67 ns | 481.57 ns | 1.00 | 0.00 | - | - | - | 24 B |
| PixelOperations_Specialized | Job-FBIBGB | .NET Core 2.1 | 2048 | 3,421.3 ns | 376.64 ns | 20.64 ns | 0.57 | 0.04 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-CETXPV | .NET Core 3.1 | 2048 | 5,542.3 ns | 790.31 ns | 43.32 ns | 1.00 | 0.00 | - | - | - | 24 B |
| PixelOperations_Specialized | Job-CETXPV | .NET Core 3.1 | 2048 | 2,972.2 ns | 70.72 ns | 3.88 ns | 0.54 | 0.00 | - | - | - | - |

Branch

| Method | Job | Runtime | Count | Mean | Error | StdDev | Ratio | RatioSD | Gen 0 | Gen 1 | Gen 2 | Allocated |
|---------------------------- |----------- |-------------- |------ |-----------:|------------:|----------:|------:|--------:|-------:|------:|------:|----------:|
| PixelOperations_Base | Job-OIBEDX | .NET 4.7.2 | 64 | 298.4 ns | 33.63 ns | 1.84 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-OIBEDX | .NET 4.7.2 | 64 | 355.5 ns | 908.51 ns | 49.80 ns | 1.19 | 0.17 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-OPAORC | .NET Core 2.1 | 64 | 220.1 ns | 13.77 ns | 0.75 ns | 1.00 | 0.00 | 0.0055 | - | - | 24 B |
| PixelOperations_Specialized | Job-OPAORC | .NET Core 2.1 | 64 | 228.5 ns | 41.41 ns | 2.27 ns | 1.04 | 0.01 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-VPSIRL | .NET Core 3.1 | 64 | 213.6 ns | 12.47 ns | 0.68 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-VPSIRL | .NET Core 3.1 | 64 | 217.0 ns | 9.95 ns | 0.55 ns | 1.02 | 0.01 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-OIBEDX | .NET 4.7.2 | 256 | 829.0 ns | 242.93 ns | 13.32 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-OIBEDX | .NET 4.7.2 | 256 | 448.9 ns | 4.04 ns | 0.22 ns | 0.54 | 0.01 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-OPAORC | .NET Core 2.1 | 256 | 863.0 ns | 1,253.26 ns | 68.70 ns | 1.00 | 0.00 | 0.0048 | - | - | 24 B |
| PixelOperations_Specialized | Job-OPAORC | .NET Core 2.1 | 256 | 309.2 ns | 66.16 ns | 3.63 ns | 0.36 | 0.03 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-VPSIRL | .NET Core 3.1 | 256 | 737.0 ns | 253.90 ns | 13.92 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-VPSIRL | .NET Core 3.1 | 256 | 212.3 ns | 1.07 ns | 0.06 ns | 0.29 | 0.01 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-OIBEDX | .NET 4.7.2 | 2048 | 5,625.6 ns | 404.35 ns | 22.16 ns | 1.00 | 0.00 | - | - | - | 24 B |
| PixelOperations_Specialized | Job-OIBEDX | .NET 4.7.2 | 2048 | 1,974.1 ns | 229.84 ns | 12.60 ns | 0.35 | 0.00 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-OPAORC | .NET Core 2.1 | 2048 | 5,467.2 ns | 537.29 ns | 29.45 ns | 1.00 | 0.00 | - | - | - | 24 B |
| PixelOperations_Specialized | Job-OPAORC | .NET Core 2.1 | 2048 | 1,985.5 ns | 4,714.23 ns | 258.40 ns | 0.36 | 0.05 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-VPSIRL | .NET Core 3.1 | 2048 | 5,888.2 ns | 1,622.23 ns | 88.92 ns | 1.00 | 0.00 | - | - | - | 24 B |
| PixelOperations_Specialized | Job-VPSIRL | .NET Core 3.1 | 2048 | 1,165.0 ns | 191.71 ns | 10.51 ns | 0.20 | 0.00 | - | - | - | - |

FromVector4_Rgb24

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19041.572 (2004/?/20H1)
Intel Core i7-8650U CPU 1.90GHz (Kaby Lake R), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=3.1.403
  [Host]     : .NET Core 3.1.9 (CoreCLR 4.700.20.47201, CoreFX 4.700.20.47203), X64 RyuJIT
  Job-XYEQXL : .NET Framework 4.8 (4.8.4250.0), X64 RyuJIT
  Job-HSXNJV : .NET Core 2.1.23 (CoreCLR 4.6.29321.03, CoreFX 4.6.29321.01), X64 RyuJIT
  Job-YUREJO : .NET Core 3.1.9 (CoreCLR 4.700.20.47201, CoreFX 4.700.20.47203), X64 RyuJIT

IterationCount=3  LaunchCount=1  WarmupCount=3

Master

| Method | Job | Runtime | Count | Mean | Error | StdDev | Ratio | RatioSD | Gen 0 | Gen 1 | Gen 2 | Allocated |
|---------------------------- |----------- |-------------- |------ |-----------:|-------------:|----------:|------:|--------:|-------:|------:|------:|----------:|
| PixelOperations_Base | Job-BPNZYS | .NET 4.7.2 | 64 | 317.7 ns | 125.40 ns | 6.87 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-BPNZYS | .NET 4.7.2 | 64 | 316.4 ns | 70.42 ns | 3.86 ns | 1.00 | 0.03 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-NYROHY | .NET Core 2.1 | 64 | 232.7 ns | 82.61 ns | 4.53 ns | 1.00 | 0.00 | 0.0055 | - | - | 24 B |
| PixelOperations_Specialized | Job-NYROHY | .NET Core 2.1 | 64 | 238.9 ns | 106.11 ns | 5.82 ns | 1.03 | 0.01 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-LSNAID | .NET Core 3.1 | 64 | 228.4 ns | 15.16 ns | 0.83 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-LSNAID | .NET Core 3.1 | 64 | 250.3 ns | 22.79 ns | 1.25 ns | 1.10 | 0.01 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-BPNZYS | .NET 4.7.2 | 256 | 975.5 ns | 1,646.67 ns | 90.26 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-BPNZYS | .NET 4.7.2 | 256 | 1,051.3 ns | 170.43 ns | 9.34 ns | 1.08 | 0.11 | 0.0172 | - | - | 72 B |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-NYROHY | .NET Core 2.1 | 256 | 793.0 ns | 69.24 ns | 3.80 ns | 1.00 | 0.00 | 0.0048 | - | - | 24 B |
| PixelOperations_Specialized | Job-NYROHY | .NET Core 2.1 | 256 | 846.8 ns | 117.07 ns | 6.42 ns | 1.07 | 0.01 | 0.0172 | - | - | 72 B |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-LSNAID | .NET Core 3.1 | 256 | 797.2 ns | 342.02 ns | 18.75 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-LSNAID | .NET Core 3.1 | 256 | 640.2 ns | 19.74 ns | 1.08 ns | 0.80 | 0.02 | 0.0172 | - | - | 72 B |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-BPNZYS | .NET 4.7.2 | 2048 | 6,178.4 ns | 1,537.81 ns | 84.29 ns | 1.00 | 0.00 | - | - | - | 24 B |
| PixelOperations_Specialized | Job-BPNZYS | .NET 4.7.2 | 2048 | 4,551.2 ns | 257.65 ns | 14.12 ns | 0.74 | 0.01 | 0.0153 | - | - | 72 B |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-NYROHY | .NET Core 2.1 | 2048 | 6,621.8 ns | 13,533.62 ns | 741.82 ns | 1.00 | 0.00 | - | - | - | 24 B |
| PixelOperations_Specialized | Job-NYROHY | .NET Core 2.1 | 2048 | 4,390.4 ns | 184.24 ns | 10.10 ns | 0.67 | 0.07 | 0.0153 | - | - | 72 B |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-LSNAID | .NET Core 3.1 | 2048 | 6,357.9 ns | 964.20 ns | 52.85 ns | 1.00 | 0.00 | - | - | - | 24 B |
| PixelOperations_Specialized | Job-LSNAID | .NET Core 3.1 | 2048 | 2,979.4 ns | 132.81 ns | 7.28 ns | 0.47 | 0.00 | 0.0153 | - | - | 72 B |

Branch

| Method | Job | Runtime | Count | Mean | Error | StdDev | Ratio | RatioSD | Gen 0 | Gen 1 | Gen 2 | Allocated |
|---------------------------- |----------- |-------------- |------ |-----------:|------------:|----------:|------:|--------:|-------:|------:|------:|----------:|
| PixelOperations_Base | Job-XYEQXL | .NET 4.7.2 | 64 | 343.2 ns | 305.91 ns | 16.77 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-XYEQXL | .NET 4.7.2 | 64 | 320.8 ns | 19.93 ns | 1.09 ns | 0.94 | 0.05 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-HSXNJV | .NET Core 2.1 | 64 | 234.3 ns | 17.98 ns | 0.99 ns | 1.00 | 0.00 | 0.0052 | - | - | 24 B |
| PixelOperations_Specialized | Job-HSXNJV | .NET Core 2.1 | 64 | 246.0 ns | 82.34 ns | 4.51 ns | 1.05 | 0.02 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-YUREJO | .NET Core 3.1 | 64 | 222.3 ns | 39.46 ns | 2.16 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-YUREJO | .NET Core 3.1 | 64 | 243.4 ns | 33.58 ns | 1.84 ns | 1.09 | 0.01 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-XYEQXL | .NET 4.7.2 | 256 | 824.9 ns | 32.77 ns | 1.80 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-XYEQXL | .NET 4.7.2 | 256 | 967.0 ns | 39.09 ns | 2.14 ns | 1.17 | 0.01 | 0.0172 | - | - | 72 B |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-HSXNJV | .NET Core 2.1 | 256 | 756.9 ns | 94.43 ns | 5.18 ns | 1.00 | 0.00 | 0.0048 | - | - | 24 B |
| PixelOperations_Specialized | Job-HSXNJV | .NET Core 2.1 | 256 | 1,003.3 ns | 3,192.09 ns | 174.97 ns | 1.32 | 0.22 | 0.0172 | - | - | 72 B |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-YUREJO | .NET Core 3.1 | 256 | 748.6 ns | 248.03 ns | 13.60 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-YUREJO | .NET Core 3.1 | 256 | 437.0 ns | 36.48 ns | 2.00 ns | 0.58 | 0.01 | 0.0172 | - | - | 72 B |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-XYEQXL | .NET 4.7.2 | 2048 | 5,751.6 ns | 704.24 ns | 38.60 ns | 1.00 | 0.00 | - | - | - | 24 B |
| PixelOperations_Specialized | Job-XYEQXL | .NET 4.7.2 | 2048 | 4,391.6 ns | 718.17 ns | 39.37 ns | 0.76 | 0.00 | 0.0153 | - | - | 72 B |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-HSXNJV | .NET Core 2.1 | 2048 | 6,202.0 ns | 1,815.18 ns | 99.50 ns | 1.00 | 0.00 | - | - | - | 24 B |
| PixelOperations_Specialized | Job-HSXNJV | .NET Core 2.1 | 2048 | 4,225.6 ns | 1,004.03 ns | 55.03 ns | 0.68 | 0.01 | 0.0153 | - | - | 72 B |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-YUREJO | .NET Core 3.1 | 2048 | 6,157.1 ns | 2,516.98 ns | 137.96 ns | 1.00 | 0.00 | - | - | - | 24 B |
| PixelOperations_Specialized | Job-YUREJO | .NET Core 3.1 | 2048 | 1,822.7 ns | 1,764.43 ns | 96.71 ns | 0.30 | 0.02 | 0.0172 | - | - | 72 B |

[JimBobSquarePants]

@antonfirsov Pushed an update that affects FromVector4_Rgb24 based on a suggestion by @Sergio0694 and It's squeezed a few more percentage performance.

| Method | Job | Runtime | Count | Mean | Error | StdDev | Ratio | RatioSD | Gen 0 | Gen 1 | Gen 2 | Allocated |
|---------------------------- |----------- |-------------- |------ |-----------:|------------:|----------:|------:|--------:|-------:|------:|------:|----------:|
| PixelOperations_Base | Job-RPFDIH | .NET 4.7.2 | 64 | 327.7 ns | 179.42 ns | 9.83 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-RPFDIH | .NET 4.7.2 | 64 | 320.8 ns | 21.37 ns | 1.17 ns | 0.98 | 0.03 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-QSMZGQ | .NET Core 2.1 | 64 | 254.8 ns | 337.29 ns | 18.49 ns | 1.00 | 0.00 | 0.0052 | - | - | 24 B |
| PixelOperations_Specialized | Job-QSMZGQ | .NET Core 2.1 | 64 | 245.3 ns | 37.22 ns | 2.04 ns | 0.97 | 0.07 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-YJZMFY | .NET Core 3.1 | 64 | 232.2 ns | 189.28 ns | 10.37 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-YJZMFY | .NET Core 3.1 | 64 | 255.4 ns | 52.39 ns | 2.87 ns | 1.10 | 0.04 | - | - | - | - |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-RPFDIH | .NET 4.7.2 | 256 | 910.1 ns | 293.07 ns | 16.06 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-RPFDIH | .NET 4.7.2 | 256 | 974.4 ns | 490.48 ns | 26.89 ns | 1.07 | 0.05 | 0.0172 | - | - | 72 B |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-QSMZGQ | .NET Core 2.1 | 256 | 849.7 ns | 1,654.73 ns | 90.70 ns | 1.00 | 0.00 | 0.0048 | - | - | 24 B |
| PixelOperations_Specialized | Job-QSMZGQ | .NET Core 2.1 | 256 | 759.9 ns | 77.06 ns | 4.22 ns | 0.90 | 0.09 | 0.0172 | - | - | 72 B |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-YJZMFY | .NET Core 3.1 | 256 | 816.1 ns | 56.07 ns | 3.07 ns | 1.00 | 0.00 | 0.0057 | - | - | 24 B |
| PixelOperations_Specialized | Job-YJZMFY | .NET Core 3.1 | 256 | 493.0 ns | 216.79 ns | 11.88 ns | 0.60 | 0.01 | 0.0172 | - | - | 72 B |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-RPFDIH | .NET 4.7.2 | 2048 | 6,394.6 ns | 2,077.05 ns | 113.85 ns | 1.00 | 0.00 | - | - | - | 24 B |
| PixelOperations_Specialized | Job-RPFDIH | .NET 4.7.2 | 2048 | 4,139.6 ns | 276.41 ns | 15.15 ns | 0.65 | 0.01 | 0.0153 | - | - | 72 B |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-QSMZGQ | .NET Core 2.1 | 2048 | 6,249.9 ns | 799.28 ns | 43.81 ns | 1.00 | 0.00 | - | - | - | 24 B |
| PixelOperations_Specialized | Job-QSMZGQ | .NET Core 2.1 | 2048 | 4,020.5 ns | 3,211.19 ns | 176.02 ns | 0.64 | 0.03 | 0.0153 | - | - | 72 B |
| | | | | | | | | | | | | |
| PixelOperations_Base | Job-YJZMFY | .NET Core 3.1 | 2048 | 6,403.5 ns | 4,626.86 ns | 253.61 ns | 1.00 | 0.00 | - | - | - | 24 B |
| PixelOperations_Specialized | Job-YJZMFY | .NET Core 3.1 | 2048 | 1,588.3 ns | 912.20 ns | 50.00 ns | 0.25 | 0.01 | 0.0172 | - | - | 72 B |

[antonfirsov]

Looks great!

@JimBobSquarePants there is one other important metric we need to check to set our expectations for #1410. Can be done by defining 2 new simple benchmark classes (baseline VS SIMD with Count = 2048):

1. Comparing Vector4 -> Rgba32 (baseline) to Vector4 -> Rgb24 (Jpeg decoder pipeline last step)
2. Comparing Rgba32 -> Vector4 (baseline) to Rgb24 -> Vector4 (Resize pipeline first step)

The smaller the difference the bigger the happiness.

[JimBobSquarePants]

Couldn't we pack directly into Rgb24 by not scaling down in the color converter and packing the planar values as bytes?

[JimBobSquarePants]

Vector4 => Rgba32 is still 2.5x faster on .NET Core 3.1 than Vector4 => Rgb24.

We'd need to have a method that goes direct to be able to cut into that since the pipeline is Vector4 => Rgba32 => Rgb24. Not difficult with hardware intrinsics based on my existing code but likely not fun with the old stuff.

What I dream of is a combination of shuffle + convert.

[antonfirsov]

Vector4 => Rgba32 is still 2.5x faster on .NET Core 3.1 than Vector4 => Rgb24.

That's bad news :(

I don't think going Vector4 => Rgb24 is the best approach here:

• It's a huge refactor strongly interfering with #1411.
• A single pipeline step would do way too much (convert colorspace + convert to byte + pack), making it very hard to maintain the code
• Ensuring that the non-HwIntrinsics path does not regress is also very expensive (The Vector<float> -> Vector<byte> conversion shall be directly integrated into the colorspace conversion code.

I'd rather suggest to do the following:

1. Color converters should convert and pack to a "Vector3" buffer (Span<float> of RGB components only, no padding for alpha)
2. Apply SimdUtils.NormalizedFloatToByteSaturate to get the Rgb24 buffer
3. Convert it further with PixelOperations<TPixel> if TPixel != Rgb24

=> Pro: likely still very fast, much more predictible amount of work, no regressions on old platforms
(But still a lot of work!)

[JimBobSquarePants]

Yeah... All my shuffle code has touched conversion between pixel formats only. The Vector4 pipeline remains untouched (_other than a speedup for converting to/from Rgba32_)

What do you mean by Color converters? The jpeg ones?

[antonfirsov]

What do you mean by Color converters? The jpeg ones?

Yes I meant that.

Couldn't we pack directly into Rgb24

I think I misunderstood you on this one. I thought you want Jpeg color converters to convert directly into Rgb24, my https://github.com/SixLabors/ImageSharp/issues/1354#issuecomment-721816361 is listing arguments against doing that.

A one-step Vector4 => Rgb24 method can help a bit, but wouldn't expect big miracle from it, choose wisely if you want to invest your time into it or not.

[JimBobSquarePants]

Just realized this was still open.