CreateThumbnail.cs

using Microsoft.Azure.Functions.Worker;
using Microsoft.Extensions.Logging;
using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Formats.Jpeg;
using SixLabors.ImageSharp.Processing;

namespace dotnet
{
    public class CreateThumbnail
    {
        private readonly ILogger<CreateThumbnail> _logger;

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

        const int thumbnailWidth = 1280;
        const int thumbnailHeight = 720;

        [Function(nameof(CreateThumbnail))]
        [BlobOutput("images-thumbnails/thumbnail.jpg", Connection = "AzureWebJobsStorage")]
        public async Task<Byte[]> Run(
            [BlobTrigger("images/{name}", Connection = "AzureWebJobsStorage")] Stream stream,
            string name
        )
        {
            _logger.LogInformation($"Processing blob\n Name: {name} \n Data: {name.Length}");

            using (var image = Image.Load(stream))
            {
                // Generate thumbnail
                image.Mutate(async x =>
                    x.Resize(
                        new ResizeOptions
                        {
                            Size = new Size(thumbnailWidth, thumbnailHeight),
                            Mode = ResizeMode.Max,
                        }
                    )
                );

                var outputBlob = new MemoryStream();
                image.Save(outputBlob, new JpegEncoder());

                // Save the thumbnail to the output blob
                _logger.LogInformation(
                    $"Finished processing blob\n Name:{name} and saved to output blob"
                );

                return outputBlob.ToArray();
            }
        }
    }
}