Here's a little function in C# to resize an image with proportional constraints. Just specific the max width and max height and this method will return a bitmap all sized up for you. I have this snipped in the form of a static **Utilities** class because that's how I use it.

ImageProcessingUtility.cs

using System;
using System.Collections.Generic;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.Linq;
using System.Web;
using System.Drawing;

namespace Utilities
{
    public static class ImageProcessingUtility
    {
        /// <summary>
        /// Scales an image proportionally.  Returns a bitmap.
        /// </summary>
        /// <param name="image"></param>
        /// <param name="maxWidth"></param>
        /// <param name="maxHeight"></param>
        /// <returns></returns>
        static public Bitmap ScaleImage(Image image, int maxWidth, int maxHeight)
        {
            var ratioX = (double)maxWidth / image.Width;
            var ratioY = (double)maxHeight / image.Height;
            var ratio = Math.Min(ratioX, ratioY);

            var newWidth = (int)(image.Width * ratio);
            var newHeight = (int)(image.Height * ratio);

            var newImage = new Bitmap(newWidth, newHeight);
            Graphics.FromImage(newImage).DrawImage(image, 0, 0, newWidth, newHeight);
            Bitmap bmp = new Bitmap(newImage);

            return bmp;
        }
    }
}

👎 not works with DPI