Question

I work on a WPF application that has multiple canvases and lots of buttons. The user cand load images to change the button background.

This is the code where I load the image in the BitmapImage object

bmp = new BitmapImage();
bmp.BeginInit();
bmp.CreateOptions = BitmapCreateOptions.IgnoreImageCache;
bmp.CacheOption = BitmapCacheOption.OnLoad;
bmp.UriSource = new Uri(relativeUri, UriKind.Relative);
bmp.EndInit();

and on EndInit() application’s memory grows very much.

One thing that makes thinks better (but doesn’t really fix the problem) is adding

bmp.DecodePixelWidth = 1024;

1024 – my maximum canvas size. But I should do this only to the images with width greater than 1024 – so how can I get the width before EndInit() ?

Answer 1

By loading the image into a BitmapFrame I think you’ll get by with just reading the metadata.

private Size GetImageSize(Uri image)
{
    var frame = BitmapFrame.Create(image);
    // You could also look at the .Width and .Height of the frame which 
    // is in 1/96th's of an inch instead of pixels
    return new Size(frame.PixelWidth, frame.PixelHeight);
}

And then you can do the following when loading the BitmapSource:

var img = new Uri(ImagePath);
var size = GetImageSize(img);
var source = new BitmapImage();
source.BeginInit();
if (size.Width > 1024)
    source.DecodePixelWidth = 1024;
source.CreateOptions = BitmapCreateOptions.IgnoreImageCache;
source.CacheOption = BitmapCacheOption.OnLoad;
source.UriSource = new Uri(ImagePath);
source.EndInit();
myImageControl.Source = source;

I tested this a few times and looked at the memory consumption in the Task Manager and the difference was massive (on a 10MP photo, I saved almost 40MB of private memory by loading it @ 1024 instead of 4272 pixels width)