添加项目文件。

DigitalImageProcessing.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.14.36408.4 d17.14
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "DigitalImageProcessing", "DigitalImageProcessing\DigitalImageProcessing.csproj", "{CC16DC64-4AF5-4AA5-83CF-EC6C2C137450}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{CC16DC64-4AF5-4AA5-83CF-EC6C2C137450}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{CC16DC64-4AF5-4AA5-83CF-EC6C2C137450}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{CC16DC64-4AF5-4AA5-83CF-EC6C2C137450}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{CC16DC64-4AF5-4AA5-83CF-EC6C2C137450}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {97DBED84-8E20-4363-B6B9-E5D9CBA483FB}
+	EndGlobalSection
+EndGlobal

DigitalImageProcessing/DigitalImageProcessing.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="FftSharp" Version="2.2.0" />
+    <PackageReference Include="SkiaSharp" Version="3.119.1" />
+  </ItemGroup>
+
+</Project>

DigitalImageProcessing/Extensions.cs

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+using SkiaSharp;
+
+namespace DigitalImageProcessing
+{
+	internal static class Extensions
+	{
+		public static void DrawTo(this float[,] values, string filename)
+		{
+			int width = values.GetLength(0);
+			int height = values.GetLength(1);
+			float min = float.MaxValue;
+			float max = float.MinValue;
+			for (int y = 0; y < height; y++)
+				for (int x = 0; x < width; x++)
+				{
+					if (values[x, y] < min) min = values[x, y];
+					if (values[x, y] > max) max = values[x, y];
+				}
+			using SKBitmap output = new(width, height);
+			using FileStream fs = new(filename, FileMode.Create, FileAccess.Write);
+			for (int y = 0; y < height; y++)
+				for (int x = 0; x < width; x++)
+				{
+					float color = (values[x, y] - min) / (max - min);
+					output.SetPixel(x, y, new SKColor(
+						(byte)(color * 128 + 128),
+						(byte)(color * 128 + 128),
+						(byte)(color * 128 + 128)));
+				}
+			output.Encode(fs, SKEncodedImageFormat.Png, 100);
+		}
+	}
+}

DigitalImageProcessing/Program.cs

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+using DigitalImageProcessing;
+using SkiaSharp;
+
+string filename = @"E:\Download\a7522809e76767bec27db9650365c56a.jpeg";
+
+int blockSize = 16;
+
+using SKBitmap bitmap = SKBitmap.Decode(filename);
+using SKCanvas canvas = new(bitmap);
+
+using SKBitmap avgGraph = new(bitmap.Width, bitmap.Height);
+using SKCanvas avgCanvas = new(avgGraph);
+
+float[,] gray = new float[bitmap.Width, bitmap.Height];
+float[,] xgradient = new float[bitmap.Width, bitmap.Height];
+float[,] ygradient = new float[bitmap.Width, bitmap.Height];
+float[,] fequency = new float[bitmap.Width, bitmap.Height];
+float[,] angle = new float[bitmap.Width, bitmap.Height];
+//float[,] direction = new float[bitmap.Width, bitmap.Height];
+
+for (int y = 0; y < bitmap.Height; y++)
+	for (int x = 0; x < bitmap.Width; x++)
+	{
+		SKColor color = bitmap.GetPixel(x, y);
+
+		// gray
+		gray[x, y] = (color.Red + color.Green + color.Blue) / 3f / 256f;
+	}
+
+for (int y = 0; y < bitmap.Height; y++)
+	for (int x = 0; x < bitmap.Width; x++)
+	{
+		// gradient
+		if (x > 0 && x < bitmap.Width - 1)
+			xgradient[x, y] = (gray[x + 1, y] - gray[x - 1, y]) / 2f;
+		if (y > 0 && y < bitmap.Height - 1)
+			ygradient[x, y] = (gray[x, y + 1] - gray[x, y - 1]) / 2f;
+		fequency[x, y] = float.Sqrt(xgradient[x, y] * xgradient[x, y] + ygradient[x, y] * ygradient[x, y]);
+		if (fequency[x, y] == 0)
+			continue;
+		angle[x, y] = float.Atan2(ygradient[x, y], xgradient[x, y]);
+		int blockx = x / blockSize;
+		int blocky = y / blockSize;
+		float dirx = float.Cos(angle[x, y]);
+		float diry = float.Sin(angle[x, y]);
+		avgCanvas.DrawLine(
+			(blockx + 0.5f - diry / 2) * blockSize,
+			(blocky + 0.5f - -dirx / 2) * blockSize,
+			(blockx + 0.5f + diry / 2) * blockSize,
+			(blocky + 0.5f + -dirx / 2) * blockSize,
+			new SKPaint { Color = SKColors.Red.WithAlpha((byte)(fequency[x, y] * 64)), StrokeWidth = 1 });
+	}
+
+using FileStream fs = new(@"E:\Download\avgGraph.png", FileMode.Create, FileAccess.Write);
+avgGraph.Encode(fs, SKEncodedImageFormat.Png, 100);
+
+xgradient.DrawTo(@"E:\Download\xgradient.png");
+ygradient.DrawTo(@"E:\Download\ygradient.png");
+fequency.DrawTo(@"E:\Download\fequency.png");
+angle.DrawTo(@"E:\Download\angle.png");
+