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ASP.NET Core: Image Utility Class for SixLabors.ImageSharp v3.x

Manipulate images on Windows and Linux web servers including creating a scatter plot and histogram, and rotating the images as needed to display properly with asp.net core web application example written in C#.

This small utility library requires adding the NuGet SixLabors.ImageSharp package (version 3.1.x) to the .NET 6/.NET 8 Project. This is compatible with Windows, Linux and MacOS.

It can resize an image based on the number of megapixels or length by width and preserve the aspect ratio if so desired.

It rotates/flips the image based on EXIF data. This is to accommodate mobile devices.

It also creates scatter plots and histograms.

See also: Bitmap Image Creation and Download for MVC Application


using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Metadata.Profiles.Exif;
using SixLabors.ImageSharp.Processing;
using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Formats.Png;
using System.IO;
using System;
using SixLabors.ImageSharp.Formats.Jpeg;

namespace ImageUtil
{
	public class GetSize
	{
		public GetSize(Stream stream)
		{
			using (Image iOriginal = Image.Load(stream))
			{
				stream.Position = 0;
				Width = iOriginal.Width;
				Height = iOriginal.Height;
			}
		}

		/// <summary>
		/// The width of the image specified in the class constructor's Stream parameter
		/// </summary>
		public int Width { get; }

		/// <summary>
		/// The height of the image specified in the class constructor's Stream parameter
		/// </summary>
		public int Height { get; }
	}

	public static class Resize
	{
		/// <summary>
		/// Resize and save an image to a Stream specifying its new width and height
		/// </summary>
		public static void SaveImage(Stream imageStream, int newWidth, int newHeight, bool preserveImageRatio, Stream saveToStream, int jpegQuality = 100)
		{
			using (Image iOriginal = Image.Load(imageStream))
			{
				imageStream.Position = 0;
				if (preserveImageRatio)
				{
					float percentWidth = newWidth / (float)iOriginal.Width;
					float percentHeight = newHeight / (float)iOriginal.Height;
					float percent = percentHeight < percentWidth ? percentHeight : percentWidth;
					newWidth = (int)Math.Round(iOriginal.Width * percent, 0);
					newHeight = (int)Math.Round(iOriginal.Height * percent, 0);
				}
				resize(imageStream, iOriginal, newWidth, newHeight, saveToStream, jpegQuality);
			}
		}

		/// <summary>
		/// Resize and save an image to a Stream specifying the number of pixels to resize to
		/// </summary>
		public static void SaveImage(Stream imageStream, int newNumberOfPixels, Stream saveToStream, int jpegQuality = 100)
		{
			using (Image iOriginal = Image.Load(imageStream))
			{
				imageStream.Position = 0;
				double ratio = Math.Sqrt(newNumberOfPixels / (double)(iOriginal.Width * iOriginal.Height));
				resize(imageStream, iOriginal, (int)Math.Round(iOriginal.Width * ratio, 0), (int)Math.Round(iOriginal.Height * ratio, 0), saveToStream, jpegQuality);
			}
		}

		private static void resize(Stream origSource, Image image, int newWidth, int newHeight, Stream saveTo, int jpegQuality)
		{
			image.Mutate(x => x.Resize(newWidth, newHeight));
			transformImage(image); // NOTE: transform image AFTER resizing it!!!
			var format = Image.DetectFormat(origSource);
			if (format.Name.ToLower() == "jpeg")
			{
				var encoder = new JpegEncoder() { Quality = jpegQuality };
				image.SaveAsJpeg(saveTo, encoder);
			}
			else
				image.Save(saveTo, format);
		}
		private static void transformImage(Image image)
		{
			IExifValue? exifOrientation = null;
			var values = image.Metadata?.ExifProfile?.Values;
			if (values != null)
				foreach (var value in values)
					if (value != null)
						if (value.Tag == ExifTag.Orientation)
							exifOrientation = value;

			if (exifOrientation == null)
				return;

			RotateMode rotateMode;
			FlipMode flipMode;
			setRotateFlipMode(exifOrientation, out rotateMode, out flipMode);

			image.Mutate(x => x.RotateFlip(rotateMode, flipMode));
			image.Metadata.ExifProfile.SetValue(ExifTag.Orientation, (ushort)1);
		}
		private static void setRotateFlipMode(IExifValue exifOrientation, out RotateMode rotateMode, out FlipMode flipMode)
		{
			var orientation = (ushort)exifOrientation.GetValue();

			switch (orientation)
			{
				case 2:
					rotateMode = RotateMode.None;
					flipMode = FlipMode.Horizontal;
					break;
				case 3:
					rotateMode = RotateMode.Rotate180;
					flipMode = FlipMode.None;
					break;
				case 4:
					rotateMode = RotateMode.Rotate180;
					flipMode = FlipMode.Horizontal;
					break;
				case 5:
					rotateMode = RotateMode.Rotate90;
					flipMode = FlipMode.Horizontal;
					break;
				case 6:
					rotateMode = RotateMode.Rotate90;
					flipMode = FlipMode.None;
					break;
				case 7:
					rotateMode = RotateMode.Rotate90;
					flipMode = FlipMode.Vertical;
					break;
				case 8:
					rotateMode = RotateMode.Rotate270;
					flipMode = FlipMode.None;
					break;
				default:
					rotateMode = RotateMode.None;
					flipMode = FlipMode.None;
					break;
			}
		}
	}

	/* CREATE A SCATTER PLOT JPEG/PNG IMAGE */
	public static class ScatterPlot
	{
		static readonly Rgba32 WHITE = new Rgba32(255, 255, 255);
		static readonly Rgba32 BLACK = new Rgba32(0, 0, 0);
		static readonly Rgba32 RED = new Rgba32(255, 0, 0);
		static readonly Rgba32 BLUE = new Rgba32(0, 0, 255);
		static readonly Rgba32 GREEN = new Rgba32(0, 192, 0);
		static readonly Rgba32 PURPLE = new Rgba32(128, 0, 128);
		static readonly Rgba32 ORANGE = new Rgba32(255, 164, 0);
		static readonly Rgba32 YELLOW = new Rgba32(255, 225, 0);
		static readonly Rgba32 MAGENTA = new Rgba32(255, 0, 255);
		static readonly Rgba32 AQUA = new Rgba32(0, 225, 255);
		static readonly Rgba32 BLUEJEAN = new Rgba32(0, 128, 255);
		static readonly Rgba32 BROWN = new Rgba32(150, 75, 50);
		static readonly Rgba32 CHARTREUSE = new Rgba32(223, 255, 0);
		static readonly Rgba32 DODGERBLUE = new Rgba32(30, 144, 255);
		static readonly Rgba32 NAVY = new Rgba32(0, 0, 128);
		static readonly Rgba32 DARKRED = new Rgba32(139, 0, 0);
		static readonly Rgba32[] colors = new Rgba32[] { WHITE, BLACK, RED, BLUE, GREEN, PURPLE, ORANGE, YELLOW, MAGENTA, AQUA, BLUEJEAN, BROWN, DODGERBLUE, CHARTREUSE, NAVY, DARKRED };
		public static void CreateJPEG(Stream stream, ScatterPlotColors backgroundColor, IEnumerable<PlotPoint> points, int width, int height, int pointSize, int jpegQuality = 100)
		{
			using (var bmp = new Image<Rgba32>(width / pointSize + 6, height / pointSize + 6, colors[(int)backgroundColor]))
				create(stream, width, height, bmp, points, pointSize, new JpegEncoder() { Quality = jpegQuality });
		}
		public static void CreateJPEG(string filename, ScatterPlotColors backgroundColor, IEnumerable<PlotPoint> points, int width, int height, int pointSize, int jpegQuality = 100)
		{
			using (var stream = File.Create(filename))
				CreateJPEG(stream, backgroundColor, points, width, height, pointSize, jpegQuality);
		}

		public static void CreatePNG(Stream stream, IEnumerable<PlotPoint> points, int width, int height, int pointSize)
		{
			using (var bmp = new Image<Rgba32>(width / pointSize + 6, height / pointSize + 6))
				create(stream, width, height, bmp, points, pointSize, new PngEncoder());
		}
		public static void CreatePNG(string filename, IEnumerable<PlotPoint> points, int width, int height, int pointSize)
		{
			using (var stream = File.Create(filename))
				CreatePNG(stream, points, width, height, pointSize);
		}

		private static double normalize(float min, float max, float value)
		{
			double x = max - min;
			if (x == 0)
				return 0;
			return (value - min) / x;
		}

		private static void create(Stream stream, int width, int height, Image<Rgba32> bmp, IEnumerable<PlotPoint> points, int pointSize, SixLabors.ImageSharp.Formats.IImageEncoder imageEncoder)
		{
			float xMax = float.MinValue, xMin = float.MaxValue, yMax = float.MinValue, yMin = float.MaxValue;
			foreach (var pt in points)
			{
				xMax = Math.Max(pt.x, xMax);
				xMin = Math.Min(pt.x, xMin);
				yMax = Math.Max(pt.y, yMax);
				yMin = Math.Min(pt.y, yMin);
			}
			float xDelta = Math.Max(1, xMax - xMin), yDelta = Math.Max(1, yMax - yMin);
			int w = width / pointSize;
			int h = height / pointSize;
			foreach (var pt in points)
			{
				int x = (int)(w * normalize(xMin, xMax, pt.x));
				int y = (int)(h * normalize(yMin, yMax, pt.y));
				bmp[x + 3, y + 3] = colors[((int)pt.color) % colors.Length];
			}
			bmp.Mutate(x => x.Flip(FlipMode.Vertical));
			bmp.Mutate(x => x.Resize(width, height));
			bmp.Save(stream, imageEncoder);
		}
	}
	public class PlotPoint
	{
		public ScatterPlotColors color { get; }
		public float x { get; }
		public float y { get; }
		public PlotPoint(float x, float y, ScatterPlotColors color)
		{
			this.x = x;
			this.y = y;
			this.color = color;
		}
	}
	public enum ScatterPlotColors
	{
		WHITE,
		BLACK,
		RED,
		BLUE,
		GREEN,
		PURPLE,
		ORANGE,
		YELLOW,
		MAGENTA,
		AQUA,
		BLUEJEAN,
		BROWN,
		CHARTREUSE,
		DODGERBLUE,
		NAVY,
		DARKRED
	}

	/* CREATE A PNG HISTOGRAM OF AN IMAGE */
	public static class Histogram
	{
		/// <summary>
		/// Create a histogram from the data in a stream
		/// </summary>
		public static MemoryStream CreatePNG(Stream stream, int width, int height, LRGB lrgb, byte alphaChannel = 128, bool clipBlackAndWhite = true, byte luminanceShade = 255)
		{
			using (var bmp = Image<Rgb24>.Load(stream))
			{
				return create(bmp, width, height, lrgb, alphaChannel, clipBlackAndWhite, luminanceShade);
			}
		}

		/// <summary>
		/// Create a histogram from the data in a file
		/// </summary>
		public static MemoryStream CreatePNG(string filename, int width, int height, LRGB lrgb, byte alphaChannel = 128, bool clipBlackAndWhite = true, byte luminanceShade = 255)
		{
			using (var bmp = Image<Rgb24>.Load(filename))
			{
				return create(bmp, width, height, lrgb, alphaChannel, clipBlackAndWhite, luminanceShade);
			}
		}

		private static MemoryStream create(Image bmp, int width, int height, LRGB lrgb, byte alpha, bool clip, byte shade)
		{
			ulong[] lumin = new ulong[256];
			ulong[] red = new ulong[256];
			ulong[] green = new ulong[256];
			ulong[] blue = new ulong[256];
			var bred = (lrgb & LRGB.RED) != 0;
			var bgreen = (lrgb & LRGB.GREEN) != 0;
			var bblue = (lrgb & LRGB.BLUE) != 0;
			var blumin = (lrgb == LRGB.LUMINANCE);
			int w = bmp.Width;
			int h = bmp.Height;
			var bmp2 = bmp.CloneAs<Rgb24>();
			for (int y = 0; y < h; y++)
			{
				bmp2.ProcessPixelRows(accessor =>
				{
					for (int x = 0; x < w; x++)
					{
						Span<Rgb24> pixelRow = accessor.GetRowSpan(y);
						var c = pixelRow[x];
						lumin[(int)Math.Round((c.R + c.G + c.B) / 3.0)]++;
						red[c.R]++;
						green[c.G]++;
						blue[c.B]++;
					}
				});
			}
			ulong max = 0;
			int a = (clip ? 1 : 0), b = (clip ? 255 : 256);
			for (int i = a; i < b; i++)
			{
				if (!blumin)
				{
					if (bred)
						if (max < red[i])
							max = red[i];
					if (bgreen)
						if (max < green[i])
							max = green[i];
					if (bblue)
						if (max < blue[i])
							max = blue[i];
				}
				else if (max < lumin[i])
					max = lumin[i];
			}
			double HEIGHTFACTOR = 256.0 / max;
			if (blumin)
			{
				using (var bmplum = new Image<Rgba32>(256, 256))
				{
					var penlum = new VerticalPen(new Rgba32(shade, shade, shade, alpha));
					for (int i = 0; i < 256; i++)
						penlum.Draw(bmplum, i, (int)(lumin[i] * HEIGHTFACTOR));
					bmplum.Mutate(x => x.Resize(width, height));
					MemoryStream ms = new MemoryStream();
					bmplum.Save(ms, new PngEncoder());
					return ms;
				}
			}
			else
			{
				using (var bmppre = new Image<Rgba32>(256, 256))
				{
					Image<Rgba32>? bmpred = null, bmpgreen = null, bmpblue = null;
					VerticalPen? penred = null, pengreen = null, penblue = null;
					if (bred)
					{
						bmpred = new Image<Rgba32>(256, 256);
						penred = new VerticalPen(new Rgba32(255, 0, 0, alpha));
					}
					if (bgreen)
					{
						bmpgreen = new Image<Rgba32>(256, 256);
						pengreen = new VerticalPen(new Rgba32(0, 255, 0, alpha));
					}
					if (bblue)
					{
						bmpblue = new Image<Rgba32>(256, 256);
						penblue = new VerticalPen(new Rgba32(0, 0, 255, alpha));
					}

					for (int i = 0; i < 256; i++)
					{
						if (bred)
							penred.Draw(bmpred, i, (int)(red[i] * HEIGHTFACTOR));
						if (bgreen)
							pengreen.Draw(bmpgreen, i, (int)(green[i] * HEIGHTFACTOR));
						if (bblue)
							penblue.Draw(bmpblue, i, (int)(blue[i] * HEIGHTFACTOR));
					}

					if (bred)
					{
						bmppre.Mutate(x => x.DrawImage(bmpred, 1));
						bmpred.Dispose();
					}
					if (bgreen)
					{
						bmppre.Mutate(x => x.DrawImage(bmpgreen, 1));
						bmpgreen.Dispose();
					}
					if (bblue)
					{
						bmppre.Mutate(x => x.DrawImage(bmpblue, 1));
						bmpblue.Dispose();
					}
					bmppre.Mutate(x => x.Resize(width, height));
					MemoryStream ms = new MemoryStream();
					bmppre.Save(ms, new PngEncoder());
					return ms;
				}
			}
		}
		internal class VerticalPen
		{
			private readonly Rgba32 color;
			public VerticalPen(Rgba32 color)
			{
				this.color = color;
			}
			public void Draw(Image<Rgba32> bmp, int row, int height)
			{
				if (height <= bmp.Height)
					for (int y = height - 1; y >= 0; y--)
						bmp[row, bmp.Height - 1 - y] = color;
			}
		}
		public enum LRGB
		{
			LUMINANCE = 0,
			RED = 1,
			GREEN = 2,
			BLUE = 4,
			REDBLUE = 1 | 4,
			REDGREEN = 1 | 2,
			BLUEGREEN = 2 | 4,
			REDGREENBLUE = 1 | 2 | 4
		}
	}
}
Example Usage

See also: console application example

This is a View in an MVC web application.


@{
	ViewData["Title"] = "/Home/UploadImages";
}

<div class="text-center">
	<h1 class="display-4">UploadImages</h1>
	<form enctype="multipart/form-data" method="post">
		<div>
			<input type="file" name="images" accept="image/jpeg, image/gif, image/png" multiple />
		</div>
		<div>
			<button type="submit" class="btn btn-primary">UPLOAD</button>
		</div>
	</form>
	@if(Model is int)
	{
		<p>@Model images saved.</p>
	}
</div>

And now the Controller code.


using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.TagHelpers;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading.Tasks;
using WebApplication1.Models;

namespace WebApplication1.Controllers
{
	public class HomeController : Controller
	{
		private readonly ILogger<HomeController> _logger;

		public HomeController(ILogger<HomeController> logger)
		{
			_logger = logger;
		}

		public IActionResult UploadImages()
		{
			return View();
		}

		[HttpPost]
		[DisableRequestSizeLimit] // NOTE: NOT RECOMMENDED - SET A LIMIT
		public IActionResult UploadImages(IFormCollection form)
		{
			int count = 0;
			foreach(var image in form.Files)
			{
				if(image.ContentType.StartsWith("image/"))
				{
					using (var openfs = image.OpenReadStream())
					{
						string filename = "thumbnail-" + image.FileName;
						if (System.IO.File.Exists(filename))
							System.IO.File.Delete(filename);
						using (var savefs = System.IO.File.OpenWrite(filename))
						{
							// NOTE: RESIZE IMAGE TO 10K PIXEL THUMBNAIL; THIS WILL ALSO FLIP AND ROTATE IMAGE AS NEEDED
							ImageUtil.Resize.SaveImage(openfs, 10000, savefs);
							count++;
						}
					}
				}	
			}
			return View(count);
		}

		public IActionResult Index()
		{
			return View();
		}

		public IActionResult Privacy()
		{
			return View();
		}

		[ResponseCache(Duration = 0, Location = ResponseCacheLocation.None, NoStore = true)]
		public IActionResult Error()
		{
			return View(new ErrorViewModel { RequestId = Activity.Current?.Id ?? HttpContext.TraceIdentifier });
		}
	}
}
.
..
kestrel
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