ImageSharp/tests/ImageSharp.Tests/Processing/Processors/Dithering/DitherTests.cs

// Copyright (c) Six Labors and contributors.
// Licensed under the Apache License, Version 2.0.

using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;
using SixLabors.ImageSharp.Processing.Processors.Dithering;
using SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison;

using Xunit;

namespace SixLabors.ImageSharp.Tests.Processing.Processors.Binarization
{
    public class DitherTests
    {
        public const PixelTypes CommonNonDefaultPixelTypes =
            PixelTypes.Rgba32 | PixelTypes.Bgra32 | PixelTypes.Rgb24 | PixelTypes.RgbaVector;

        public static readonly string[] CommonTestImages = { TestImages.Png.CalliphoraPartial, TestImages.Png.Bike };

        public static readonly TheoryData<IDither> ErrorDiffusers
            = new TheoryData<IDither>
            {
                KnownDitherings.Atkinson,
                KnownDitherings.Burks,
                KnownDitherings.FloydSteinberg,
                KnownDitherings.JarvisJudiceNinke,
                KnownDitherings.Sierra2,
                KnownDitherings.Sierra3,
                KnownDitherings.SierraLite,
                KnownDitherings.StevensonArce,
                KnownDitherings.Stucki,
            };

        public static readonly TheoryData<IDither> OrderedDitherers
            = new TheoryData<IDither>
            {
                KnownDitherings.BayerDither8x8,
                KnownDitherings.BayerDither4x4,
                KnownDitherings.OrderedDither3x3,
                KnownDitherings.BayerDither2x2
            };

        private static readonly ImageComparer ValidatorComparer = ImageComparer.TolerantPercentage(0.05f);

        private static IDither DefaultDitherer => KnownDitherings.BayerDither4x4;

        private static IDither DefaultErrorDiffuser => KnownDitherings.Atkinson;

        /// <summary>
        /// The output is visually correct old 32bit runtime,
        /// but it is very different because of floating point inaccuracies.
        /// </summary>
        private static readonly bool SkipAllDitherTests =
            !TestEnvironment.Is64BitProcess && string.IsNullOrEmpty(TestEnvironment.NetCoreVersion);

        [Theory]
        [WithFile(TestImages.Png.CalliphoraPartial, PixelTypes.Rgba32)]
        public void ApplyDiffusionFilterInBox<TPixel>(TestImageProvider<TPixel> provider)
            where TPixel : struct, IPixel<TPixel>
        {
            if (SkipAllDitherTests)
            {
                return;
            }

            provider.RunRectangleConstrainedValidatingProcessorTest(
                (x, rect) => x.Dither(DefaultErrorDiffuser, rect),
                comparer: ValidatorComparer);
        }

        [Theory]
        [WithFile(TestImages.Png.CalliphoraPartial, PixelTypes.Rgba32)]
        public void ApplyDitherFilterInBox<TPixel>(TestImageProvider<TPixel> provider)
            where TPixel : struct, IPixel<TPixel>
        {
            if (SkipAllDitherTests)
            {
                return;
            }

            provider.RunRectangleConstrainedValidatingProcessorTest(
                (x, rect) => x.Dither(DefaultDitherer, rect),
                comparer: ValidatorComparer);
        }

        [Theory]
        [WithFile(TestImages.Png.Filter0, CommonNonDefaultPixelTypes)]
        public void DiffusionFilter_ShouldNotDependOnSinglePixelType<TPixel>(TestImageProvider<TPixel> provider)
            where TPixel : struct, IPixel<TPixel>
        {
            if (SkipAllDitherTests)
            {
                return;
            }

            // Increased tolerance because of compatibility issues on .NET 4.6.2:
            var comparer = ImageComparer.TolerantPercentage(1f);
            provider.RunValidatingProcessorTest(x => x.Dither(DefaultErrorDiffuser), comparer: comparer);
        }

        [Theory]
        [WithFileCollection(nameof(CommonTestImages), nameof(ErrorDiffusers), PixelTypes.Rgba32)]
        public void DiffusionFilter_WorksWithAllErrorDiffusers<TPixel>(
            TestImageProvider<TPixel> provider,
            IDither diffuser)
            where TPixel : struct, IPixel<TPixel>
        {
            if (SkipAllDitherTests)
            {
                return;
            }

            provider.RunValidatingProcessorTest(
                x => x.Dither(diffuser),
                testOutputDetails: diffuser.GetType().Name,
                comparer: ValidatorComparer,
                appendPixelTypeToFileName: false);
        }

        [Theory]
        [WithFile(TestImages.Png.Filter0, CommonNonDefaultPixelTypes)]
        public void DitherFilter_ShouldNotDependOnSinglePixelType<TPixel>(TestImageProvider<TPixel> provider)
            where TPixel : struct, IPixel<TPixel>
        {
            if (SkipAllDitherTests)
            {
                return;
            }

            provider.RunValidatingProcessorTest(
                x => x.Dither(DefaultDitherer),
                comparer: ValidatorComparer);
        }

        [Theory]
        [WithFileCollection(nameof(CommonTestImages), nameof(OrderedDitherers), PixelTypes.Rgba32)]
        public void DitherFilter_WorksWithAllDitherers<TPixel>(
            TestImageProvider<TPixel> provider,
            IDither ditherer)
            where TPixel : struct, IPixel<TPixel>
        {
            if (SkipAllDitherTests)
            {
                return;
            }

            provider.RunValidatingProcessorTest(
                x => x.Dither(ditherer),
                testOutputDetails: ditherer.GetType().Name,
                comparer: ValidatorComparer,
                appendPixelTypeToFileName: false);
        }
    }
}