How To Handle Image as Background to CAD Application

My application is used to design airports for a 开发者_Go百科flight simulator. Users can add one or more images as background. The image(s) can be sized accurately and then used as a template to lay down features such as runways, aprons and so on.

I use a third party graphics library (Piccolo) which has an image class (as far as I can see it is a simple wrapper for System.Drawing.Image).

So far I have done little except allow the user to add an image, size it and so on. It will be no surprise that users sometimes complain of poor performance. We tell them not to load large images (up to 100k seem OK) but don't stop them and 100Mb bitmaps have been used with horrible results.

I need to fix this in a couple of ways. First by converting any image they use to an efficient format (size vs definition) and second by ensuring that the loaded image is suitably sized for the dimensions - at the moment I don't do anything specific to deal with the resizing of say a 2000 x 2000 image to fit a 500 x 500 area of the display.

The default 1:1 display of the application represents 1m per pixel. Once the user has resized the image to fit accurately would I be right in thinking that the best resoultion for the image would be to resample it to that size? I am aware that if the user zooms in way past 1:1 which they will probably do then the clarity of the image will fall.

My ignorance of handling images is complete. I have looked at some image manipulation libraries (ImageMagick and the free version of dotIamge) first for converting the input image to a standard one and second for resizing -resampling. The truth is that they do far more than I need.

Any pointer much appreciated.

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Yes, resampling so that the bitmap doesn't constantly have to be rescaled for every paint should make a big difference. The default Graphics.InterpolationMode makes pretty images but is not cheap.

Another biggie is the pixel format of the bitmap. Format32bppPArgb is 10 times faster than any of the others on most video adapters.

    private static Bitmap Resample(Image img, Size size) {
        var bmp = new Bitmap(size.Width, size.Height, System.Drawing.Imaging.PixelFormat.Format32bppPArgb);
        using (var gr = Graphics.FromImage(bmp)) {
            gr.DrawImage(img, new Rectangle(Point.Empty, size));
        }
        return bmp;
    }