inabox/InABox.Mobile/InABox.Mobile.Android/ImageToolsDroid.cs

using System;
using System.Drawing;
using System.IO;
using Android.Graphics;
using Bitmap = Android.Graphics.Bitmap;

[assembly: Xamarin.Forms.Dependency(typeof(InABox.Mobile.Android.ImageToolsDroid))]
namespace InABox.Mobile.Android
{
    public class ImageToolsDroid: IImageTools
    {
        public byte[] CreateThumbnail(byte[] source, float maxwidth, float maxheight)
        {
            byte[] result = { };
            using (var image = BitmapFactory.DecodeByteArray(source, 0, source.Length))
            {  
                if (image != null)
                {
                    var size = new Size((int)image.GetBitmapInfo().Height, (int)image.GetBitmapInfo().Width);
                    if ((size.Width > 0) && (size.Height > 0))
                    {
                        var maxFactor = Math.Min(maxwidth / size.Width, maxheight / size.Height);
                        var width = maxFactor * size.Width;
                        var height = maxFactor * size.Height;
                        using (var tgt = Bitmap.CreateScaledBitmap(image, (int)height, (int)width, true))
                        {
                            if (tgt != null)
                            {
                                using (var ms = new MemoryStream())
                                {
                                    tgt.Compress(Bitmap.CompressFormat.Jpeg, 95, ms);
                                    result = ms.ToArray();
                                }

                                tgt.Recycle();
                            }
                        }
                    }
                    image.Recycle();
                }
            }
            return result;
        }
    }
}