Why would you create a new Bitmap to convert to BitmapImage? - wpf

Question

I have a converter in some legacy code, that is doing something that seems wrong, but I don't know bitmaps very well.
It looks like it's based on https://stackoverflow.com/a/3427114/57883
with some added capabilities.
using System;
using System.Collections.Generic;
using System.Drawing.Imaging;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Text;
using System.Windows.Data;
using System.Windows.Media.Imaging;
namespace CompanyName.Converters
{
[ValueConversion(typeof(System.Drawing.Image), typeof(System.Windows.Media.ImageSource))]
/// <summary>
/// One-way converter from System.Drawing.Image to System.Windows.Media.ImageSource
/// </summary>
public class ImageConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
// empty images are empty...
if (value == null)
{
return null;
}
if (value.GetType() == typeof(System.Drawing.Image))
{
var image = (System.Drawing.Image)value;
// Winforms Image we want to get the WPF Image from...
var bitmap = new System.Windows.Media.Imaging.BitmapImage();
bitmap.BeginInit();
MemoryStream memoryStream = new MemoryStream();
// Save to a memory stream...
image.Save(memoryStream, ImageFormat.Bmp);
// Rewind the stream...
memoryStream.Seek(0, System.IO.SeekOrigin.Begin);
bitmap.StreamSource = memoryStream;
bitmap.EndInit();
bitmap.Freeze();
return bitmap;
}
else if (value.GetType() == typeof(System.Drawing.Bitmap))
{
var image = value as System.Drawing.Bitmap;
System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(image);
using (MemoryStream memory = new MemoryStream())
{
bitmap.Save(memory, ImageFormat.Png);
memory.Position = 0;
BitmapImage bitmapImage = new BitmapImage();
bitmapImage.BeginInit();
bitmapImage.StreamSource = memory;
bitmapImage.CacheOption = BitmapCacheOption.OnLoad;
bitmapImage.EndInit();
bitmapImage.Freeze();
return bitmapImage;
}
}
return null;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return null;
}
}
}
Why in the world would you System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(image); ? isn't this just creating a copy of the bitmap in memory without any benefit? Is this just horrible code or is there a legitimate reason to copy the bitmap before converting it?

Answer 1

Copying the bitmap via the constructor without explicitly specifying the PixelFormat will result in the image being converted to 32bpp argb, which will in turn prevent problems arising if you try to bind to an image with a pixel format that the target doesn't support. In the case of WPF the Image control does render indexed images correctly but there might be other formats or other control types that will fail. The original author was probably just trying to cover all bases.