png image from ShellFile (Windows)

Hi Experts,

If I have the full path to a file in Windows, how can I create a png image out of its thumbnail with a specific width and height?

ShellFile shellFile = ShellFile.FromFilePath("c:\\test\\myfile.txt");
Bitmap shellThumb = shellFile.Thumbnail.ExtraLargeBitmap;

That code is fine to produce an extra large bitmap, but I need a png of say, 100x100 (or any size)...

Thanks!
Mike
LVL 1
threadyAsked:
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Randy DownsOWNERCommented:
Try this.

Scaling code. The most difficult part of generating thumbnails is probably scaling them. It isn't a good idea just to decrease all dimensions by 50% if the images are of different sizes, because then some thumbnails will be much larger than others.

Instead:
The scaling logic here caps each dimension to 40 pixels. Based on the larger dimension, it scales the entire image.

Note:
I tested this code with different sizes of images, both horizontally larger and vertically larger, and it worked correctly.

using System;
using System.Drawing;

class Program
{
    static void Main()
    {
	const string input = "C:\\background1.png";
	const string output = "C:\\thumbnail.png";

	// Load image.
	Image image = Image.FromFile(input);

	// Compute thumbnail size.
	Size thumbnailSize = GetThumbnailSize(image);

	// Get thumbnail.
	Image thumbnail = image.GetThumbnailImage(thumbnailSize.Width,
	    thumbnailSize.Height, null, IntPtr.Zero);

	// Save thumbnail.
	thumbnail.Save(output);
    }

    static Size GetThumbnailSize(Image original)
    {
	// Maximum size of any dimension.
	const int maxPixels = 40;

	// Width and height.
	int originalWidth = original.Width;
	int originalHeight = original.Height;

	// Compute best factor to scale entire image based on larger dimension.
	double factor;
	if (originalWidth > originalHeight)
	{
	    factor = (double)maxPixels / originalWidth;
	}
	else
	{
	    factor = (double)maxPixels / originalHeight;
	}

	// Return thumbnail size.
	return new Size((int)(originalWidth * factor), (int)(originalHeight * factor));
    }
}

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threadyAuthor Commented:
Awesome, thanks Randy!
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