https://hacksbyme.net/2018/05/12/optimize-your-images-with-imageprocessor/

ImageTypes.cs

namespace MyEpiSite.Business.Rendering
{
    public class ImageType
    {
        public int? DefaultImgWidth { get; set; } //this size will be used in browsers that don't support the picture element
        public int[] SrcSetWidths { get; set; } // the different image widths you want the browser to select from
        public string[] SrcSetSizes { get; set; }
        public double HeightRatio { get; set; }
        public int Quality { get; set; }

        public ImageType()
        {
            Quality = 80; //default quality
        }
    }

    public static class ImageTypes
    {
        public static ImageType HeroImage = new ImageType
        {
            DefaultImgWidth = 1280,
            SrcSetWidths = new[] { 375, 750, 1440, 1920 },
            SrcSetSizes = new[] { "100vw" },
            HeightRatio = 0.5625 //16:9
        };

        public static ImageType Thumbnail = new ImageType
        {
            DefaultImgWidth = 200,
            SrcSetWidths = new[] {200, 400}, 
            SrcSetSizes = new[] { "200px" },
            HeightRatio = 1 //square
        };
    }
}