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.NET: Image Utility for SixLabors.ImageSharp

Manipulate images on Windows, Linux and MacOS machines including creating a histogram and rotating them as needed to display properly with a C# console application example.

This small utility library requires adding the NuGet SixLabors.ImageSharp package (version 1.0.4) to the .NET Core/.NET 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 histograms.


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 (SixLabors.ImageSharp.Image iOriginal = SixLabors.ImageSharp.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; }
	}

	static public 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 (SixLabors.ImageSharp.Image iOriginal = SixLabors.ImageSharp.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 (SixLabors.ImageSharp.Image iOriginal = SixLabors.ImageSharp.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, SixLabors.ImageSharp.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 = SixLabors.ImageSharp.Image.DetectFormat(origSource);
			if (format.Name.ToLower() == "jpeg")
			{
				var encoder = new JpegEncoder();
				encoder.Quality = jpegQuality;
				image.SaveAsJpeg(saveTo, encoder);
			}
			else
				image.Save(saveTo, format);
		}
		private static void transformImage(SixLabors.ImageSharp.Image image)
		{
			IExifValue exifOrientation = image.Metadata?.ExifProfile?.GetValue(ExifTag.Orientation);

			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;
			}
		}
	}
	internal class VerticalPen
	{
		private readonly Rgba32 color;
		public VerticalPen(Rgba32 color)
		{
			this.color = color;
		}
		public void Draw(SixLabors.ImageSharp.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;
		}
	}
	static public class Histogram
	{
		/// <summary>
		/// Create a histogram from the data in a stream
		/// </summary>
		static public MemoryStream CreatePNG(Stream stream, int width, int height, LRGB lrgb, byte alphaChannel = 128, bool clipBlackAndWhite = true, byte luminanceShade = 255)
		{
			using (var bmp = SixLabors.ImageSharp.Image<Rgb24>.Load(stream))
			{
				return create(bmp, width, height, lrgb, alphaChannel, clipBlackAndWhite, luminanceShade);
			}
		}

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

		static private MemoryStream create(SixLabors.ImageSharp.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++)
			{
				Span<Rgb24> pixelRow = bmp2.GetPixelRowSpan(y);
				for (int x = 0; x < w; x++)
				{
					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 SixLabors.ImageSharp.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 SixLabors.ImageSharp.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;
				}
			}
		}
		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: web application example


namespace ConsoleApp1
{
	class Program
	{
		static void Main(string[] args)
		{
			if(args.Length > 0)
			{
				using (var openfs = System.IO.File.OpenRead(args[0]))
				{
					// NOTE: GET IMAGE SIZE
					var size = new ImageUtil.GetSize(openfs);

					System.Console.WriteLine("IMAGE SIZE: " + size.Width + " x " + size.Height);

					if (args.Length > 1)
					{
						if (System.IO.File.Exists(args[1]))
							System.IO.File.Delete(args[1]);
						using (var savefs = System.IO.File.OpenWrite(args[1]))
						{
							System.Console.WriteLine("RESIZING IMAGE TO 10K PIXEL THUMBNAIL");

							// NOTE: RESIZE IMAGE TO 10K PIXELS; THIS WILL ALSO FLIP AND ROTATE IMAGE AS NEEDED
							ImageUtil.Resize.SaveImage(openfs, 10000, savefs);
						}
					}
				}

				System.Console.WriteLine("CREATING LUMINANCE HISTOGRAM: histogram.png");

				// NOTE: CREATE HISTOGRAM WHICH IS RETURNED AS A MEMORY STREAM OF A PORTABLE NETWORK GRAPHICS (PNG) IMAGE FILE
				using (var histogram = ImageUtil.Histogram.CreatePNG(args[0], 300, 150, ImageUtil.Histogram.LRGB.LUMINANCE, 128))
				{
					if (System.IO.File.Exists("histogram.png"))
						System.IO.File.Delete("histogram.png");
					System.IO.File.WriteAllBytes("histogram.png", histogram.ToArray());
				}
			}
			else
				System.Console.WriteLine("argument one is path to image, argument two [optional] is path to resized image");
		}
	}
}

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