ImageSharp is a new, fully featured, fully managed, cross-platform, 2D graphics API. Designed to democratize image processing, ImageSharp brings you an incredibly powerful yet beautifully simple API. [Ref]

Having an azure function for your image resizing needs ,thumbnails, can be quite handy whether in production or a dev environment.

Code sample for image resize by providing height and width:

using System.IO;
using System.Numerics;
using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Formats.Jpeg;
using SixLabors.ImageSharp.Formats.Png;
using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;
using SixLabors.ImageSharp.Processing.Drawing;
using SixLabors.ImageSharp.Processing.Transforms;
using SixLabors.Primitives;
using SixLabors.Shapes;

namespace AzureFuncSamples.ImageResize
{
    public static class ImageResizeFunctions
    {
        public static byte[] GenerateThumbnailByWidthHeight(Image<Rgba32> image, int w, int h)
        {
            image.Mutate(x => x.Resize(w, h));
            using (var returnImageStream = new MemoryStream())
            {
                image.Save(returnImageStream, new JpegEncoder());
                return returnImageStream.ToArray();
            }
        }
    }
}

Actual Azure Function:

using System.IO;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
using Microsoft.Azure.WebJobs.Host;
using SixLabors.ImageSharp;
using Path = System.IO.Path;

namespace AzureFuncSamples.ImageResize
{
    public static class ImageResizer
    {
        [FunctionName("ImageResizeByWidthHeight")]
        public static IActionResult ImageResizeByWidthHeight([HttpTrigger(AuthorizationLevel.Anonymous, "post"
            , Route = "imageresize/{w=w}/{h=h}")]HttpRequest req, int w, int h, TraceWriter log)
        {
            using (var imageStream = Image.Load(req.Body))
            {
                if ((w <= 0 || w > imageStream.Width) || (h <= 0 || h > imageStream.Height))
                    return new BadRequestObjectResult("Provide proper width and height");
                return new FileContentResult(ImageResizeFunctions.GenerateThumbnailByWidthHeight(imageStream, w, h), "image/jpeg");
            }
        }
    }
}

And that’s it, neat and clean.

As ImageSharp is a cross-platform library, you can use this in .Net Framework ( Aps.net, WebApi) or .Net Core.

Complete code is available in my GitHub repo : azure-function-samples