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ASP.NET Core: Bitmap Image Creation and Download

Download any file type from a controller in ASP.NET MVC using File.

This example creates a bitmap (jpeg) and sends it to the browser. It requires the NuGet package SixLabors.ImageSharp v1.0.4.

See also: SixLabors.ImageSharp Image Utility Class

See also: Delete a file after uploading to the browser

The code that follows will create and then alternate between these four images:

The modified HomeController.cs file:

// HomeController.cs
using Microsoft.AspNetCore.Mvc;
using SixLabors.ImageSharp;
using SixLabors.ImageSharp.PixelFormats;

namespace WebApplication1.Controllers
{
	public class HomeController : Controller
	{
		static private byte mod(int x, int y) // NOTE: only returns values 0 to 255
		{
			if ((y & 1) == 0) // NOTE: then base of 2 - no need for division
				return (byte)(x & (y - 1));
			else
				return (byte)(x % y);
		}
		static private void Image0(Image<Rgb24> bmp) // NOTE: this will create a colorful bitmap with colorful stars
		{
			// NOTE: loop through every pixel of the bitmap
			for (int x = 0; x < bmp.Width; x++)
				for (int y = 0; y < bmp.Height; y++)
				{
					byte p = (byte)(x * y >> 8), c = mod(p, 3), z = 255; // NOTE: "z" can be any shade between 0 and 255
					bmp[x, y] = new Rgb24(c == 0 ? p : z, c == 1 ? p : z, c == 2 ? p : z); // NOTE: set the color of the pixel at (x, y)
				}
		}
		static private void Image1(Image<Rgb24> bmp) // NOTE: this will create a bitmap with a pattern that repeats
		{
			// NOTE: loop through every pixel of the bitmap
			for (int x = 0; x < bmp.Width; x++)
				for (int y = 0; y < bmp.Height; y++)
				{
					byte p = mod(x * y, 256), c = mod(p, 3), z = 0; // NOTE: "z" can be any shade between 0 and 255
					bmp[x, y] = new Rgb24(c == 0 ? p : z, c == 1 ? p : z, c == 2 ? p : z); // NOTE: set the color of the pixel at (x, y)
				}
		}
		static private void Image2(Image<Rgb24> bmp) // NOTE: this will create a bitmap with a unique diagonal pattern
		{
			// NOTE: loop through every pixel of the bitmap
			for (int x = 0; x < bmp.Width; x++)
				for (int y = 0; y < bmp.Height; y++)
				{
					byte p = mod(x, y), c = mod(p, 3), z = 127; // NOTE: "z" can be any shade between 0 and 255
					bmp[x, y] = new Rgb24(c == 0 ? p : z, c == 1 ? p : z, c == 2 ? p : z); // NOTE: set the color of the pixel at (x, y)
				}
		}
		static private void Image3(Image<Rgb24> bmp) // NOTE: this will create a bitmap of noise
		{
			var rand = new Random();
			// NOTE: loop through every pixel of the bitmap
			for (int x = 0; x < bmp.Width; x++)
				for (int y = 0; y < bmp.Height; y++)
				{
					byte p = mod(rand.Next(), 256), c = mod(p, 3), z = 255; // NOTE: "z" can be any shade between 0 and 255
					bmp[x, y] = new Rgb24(c == 0 ? p : z, c == 1 ? p : z, c == 2 ? p : z); // NOTE: set the color of the pixel at (x, y)
				}
		}
		public IActionResult Index()
		{
			int image = int.Parse(Request.Cookies["image"] ?? "0");
			Response.Cookies.Append("image", (image + 1).ToString());
			const int shift = 9;
			const int width = 1 << shift, height = 1 << shift;
			using (var bmp = new Image<Rgb24>(width, height)) // NOTE: create 24-bit bitmap
			{
				switch (mod(image, 4))
				{
					case 0:
						Image0(bmp);
						break;
					case 1:
						Image1(bmp);
						break;
					case 2:
						Image2(bmp);
						break;
					case 3:
						Image3(bmp);
						break;
				}
				byte[] data;
				using (var ms = new MemoryStream())
				{
					bmp.SaveAsJpeg(ms); // NOTE: save the bitmap as a JPEG image to the stream
					data = ms.ToArray();

				}
				// NOTE: alternatively, send the data to the browser as a download with the file name "attachment.jpg" by uncommenting the following line
				// return File(data, System.Net.Mime.MediaTypeNames.Image.Jpeg, "attachment.jpg");

				return File(data, System.Net.Mime.MediaTypeNames.Image.Jpeg); // NOTE: send the data to the browser as a file of mime type "image/jpeg"
			}
		}
	}
}

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