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c#.netgraphicsgdi+image-scaling

Scaling Image to multiple sizes for Deep Zoom

Lets assume I have a bitmap with a square aspect and width of 2048 pixels.

In order to create a set of files need by Silverlight's DeepZoomImageTileSource I need to scale this bitmap to 1024 then to 512 then to 256 etc down to 1 pixel image.

There are two, I suspect naive, approaches:-

  1. For each image required scale the original full size image to the required size. However it seems excessive to be scaling the full image to the very small sizes.
  2. Having scaled from one level to the next discard the original image and scale each sucessive scaled image as the source of the next smaller image. However I suspect that this would generate images in the 256-64 range with poor fidelity than using option 1.

Note unlike with the Deep Zoom Composer this tool is expected to act in an on-demand fashion hence it needs to complete in a reasonable timeframe (tops 30 seconds). On the pluse side I'm only creating a single multiscale image not a pyramid of mutliple high-res images.

I am outside my comfort zone here, any graphics experts got any advice? Am I wrong about point 2? Is point 1 reasonably performant and I'm worrying about nothing? Option 3?

Solution

  • About 1: This seems the best way. And it is not that excessive if you don't reload the source image each time.

    About 2: Yes, you would looses (some) quality by scaling in steps.

    I think 30 sec should be sufficient to scale a picture (a few times). Any optimization would be in the area of caching the results.