multiple big images on canvas in WPF - rendering problems

Dominik Gruber

16y9.4k

I am trying to put several images dynamically onto a canvas. The images are of bigger size (e.g. 9 MB on disc, 200 MB of physical memory when decoded, resolution of 10200 x 7019).
If I add 2 images, everything is working fine. If I try to add another image, the Image is there on the canvas (meaning it reacts on mouse events) but it is not rendered - meaning it is invisible. I have about 1 GB of free physical memory available. When 2 images are loaded I still have 600 MB of free physical memory - but I cant load any more images. I tried to set the images' DecodeBitmapWith/Height attributes to have a smaller rendersize, but images are rendered black or look weird. Image.Rendersize attribute doesnt work in this context.

I assume it has something to do with memory management. For better understanding here is my code:

ofd = new OpenFileDialog();
if ((bool)ofd.ShowDialog(this))
{
    string[] images = ofd.FileNames;
    foreach (string image in images) 
    {        
        Uri imgsource = new Uri(image);
        BitmapImage bim = new BitmapImage();
        bim.BeginInit();
        //bim.DecodePixelWidth = 3509;
        bim.DecodePixelHeight = 10200;
        bim.CacheOption = BitmapCacheOption.OnLoad;
        bim.UriSource = imgsource;
        bim.EndInit();
        Image img = new Image();
        img.Source = bim
        canvas1.Children.Add(img);
        img.AllowDrop = true;
        Canvas.SetLeft(img, (canvas1.Children.Count)* 20);
        Canvas.SetTop(img, (canvas1.Children.Count) * 20);
}

I hope anyone can help me with this.
Thanks in advance and best regards
Nick

2 Replies

Know the answer? Post it — somebody with the same question will find it here.

Woody Wood8y ago
About 8 years on and I hope your still around :)
I am having a similar issue which is really vexing me and your post is the only one I can find remotely similar to the issues I am having.

I am converting the pages of a PDF file into images with ghostscript and placing them as a dynamically created image onto a canvas at run time.

I have found that with a 50 page document I have, if I catch it at 500dpi then only 10 pages appear. If I reduce this to 400 dpi then I get 14 pages. At 100dpi I can get all 50 pages but they are small on my canvas and I want to be able to capture at high DPI's in some instances.

Besides the solution/work around you offered, did you find any other reason or solution? Is anyone else able to give any insight? I've been stumped on this for about 2 weeks!!
Dominik Gruber16y ago
Still no solution. Any ideas?

Edit1:
Additional information: the images have been scanned at 600 dpi.

When loaded into BitmapImage the origianal Image is downscaled to 96 dpi. How can I keep the original size of the image?
I tried setting the DecodePixelWidth and -Height properties to the original size (7019x10200) of the image, but WPF keeps downscaling it to 1123.04X1632.

Edit2:
Kind of a solution to the DPI problem:
The BitmapImage is the source of an Image element. The Image.Width and Image.Height properties are set to BitmapImage.PixelWidth and BitmapImage.PixelHeight and the Image.Stretch property is set to Uniform. This renders the Image to its original PixelSize. But nonetheless the original Image is first downscaled to fit the 96 dpi screen, then stretched again to fit the ImageElement...if you have a better solution please feel free to post it here.

Thanks
Nick