I've got a situation where I need to resize a large number of images. These images are stored as .jpg files on the file system currently, but I expect to just have byte[] in memory later on in the project. The source image size is variable, but the output should be 3 different predetermined sizes. Aspect ratios should be preserved, padding the original image with white space (ie, a really tall image would be resized to fit within the square target image size, with large areas of white on the left and right).
I initially built the project targeting .NET 2.0, and using System.Drawing classes to perform the load/resize/save. Relevant code includes:
original = Image.FromFile(inputFile); //NOTE: Reused for each of the 3 target sizes
Bitmap resized = new Bitmap(size, size);
//Draw the image to a new image of the intended size
Graphics g = Graphics.FromImage(resized);
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
g.Clear(Color.White);
g.DrawImage(original, center - width / 2f, center - height / 2f, width, height);
g.Dispose();
//Save the new image to the output path
resized.Save(outputFile, ImageFormat.Jpeg);
I wanted to port this project to .NET 3.5, so tried using the System.Windows.Media classes to perform the same function. I got it working, however performance is terrible; processing time per image is about 50x longer. The vast majority of the time is spent loading the image. Relevant code includes:
BitmapImage original = new BitmapImage(); //Again, reused for each of the 3 target sizes
original.BeginInit();
original.StreamSource = new MemoryStream(imageData); //imageData is a byte[] of the data loaded from a FileStream
original.CreateOptions = BitmapCreateOptions.None;
original.CacheOption = BitmapCacheOption.Default;
original.EndInit(); //Here's where the vast majority of the time is spent
original.Freeze();
// Target Rect for the resize operation
Rect rect = new Rect(center - width / 2d, center - height / 2d, width, height);
// Create a DrawingVisual/Context to render with
DrawingVisual drawingVisual = new DrawingVisual();
using (DrawingContext drawingContext = drawingVisual.RenderOpen())
{
drawingContext.DrawImage(original, rect);
}
// Use RenderTargetBitmap to resize the original image
RenderTargetBitmap resizedImage = new RenderTargetBitmap(
size, size, // Resized dimensions
96, 96, // Default DPI values
PixelFormats.Default); // Default pixel format
resizedImage.Render(drawingVisual);
// Encode the image using the original format and save the modified image
SaveImageData(resizedImage, outputFile);
Am I doing something wrong here, to take so much time? I've tried just using the constructor on BitmapImage that takes a URI, same performance issue there. Anyone done anything like this before, know if there's a more performance-minded way to do this? Or am I just going to need to use System.Drawing still? Thanks!