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c#imageimage-processingclip

Clipping images

I have the following code to work with images from a stream. My intention is to pick a subregion of it and resize it to 100x100. I do not know the format of the image beforehand.

var image = new Bitmap(stream);

var destArea = new Rectangle(0, 0, 100, 100);
var srcArea = new Rectangle(x, y, width, height);

var gfx = Graphics.FromImage(image);
gfx.DrawImage(image, destArea, srcArea, GraphicsUnit.Pixel);

var ms = new MemoryStream();
image.Save(ms, image.RawFormat);

For some reason, this is taking the subregion I want, resizing it and putting it on top of the original image, so that the result is a mixture of the original and my desired result.

I have been through several guides, posts on image processing but I still don't know for sure where am I wrong. Would you mind to help me out?

Also, I would really appreciate if you also explained to me what is it that I'm missing (a little bit of theory behind the code).

Thanks!

Solution

  • If you're resizing an image, you'll need a new image object into which you'll put your resized image. What you're missing is the creation of the new 100x100 image. Here's how your code should look:

    var image = new Bitmap(stream);
var destArea = new Rectangle(0, 0, 100, 100);
var srcArea = new Rectangle(x, y, width, height);

// Destination image
var destImage = new Bitmap(destArea.Width, destArea.Height);

var gfx = Graphics.FromImage(destImage);
gfx.DrawImage(image, destArea, srcArea, GraphicsUnit.Pixel);

var ms = new MemoryStream();
destImage.Save(ms, image.RawFormat);

    I would also recommend wrapping all the GDI+ objects in using statements, as they generally don't play well with garbage collection.