[ACCEPTED]-GDIplus Scale Bitmap-gdi+
Compute the new width and height (if you 8 have the scaling factors)
float newWidth = horizontalScalingFactor * (float) originalBitmap->GetWidth();
float newHeight = verticalScalingFactor * (float) originalBitmap->GetHeight();
or the scaling 7 factors if the new dimensions are known
float horizontalScalingFactor = (float) newWidth / (float) originalBitmap->GetWidth();
float verticalScalingFactor = (float) newHeight / (float) originalBitmap->GetHeight();
Create 6 a new empty bitmap with sufficient space 5 for the scaled image
Image* img = new Bitmap((int) newWidth, (int) newHeight);
Create a new Graphics 4 to draw on the created bitmap:
Graphics g(img);
Apply a scale 3 transform to the Graphics and draw the image 2
g.ScaleTransform(horizontalScalingFactor, verticalScalingFactor);
g.DrawImage(originalBitmap, 0, 0);
img is now another Bitmap with a scaled version 1 of the original image.
The solution proposed by mhcuervo works well, except if the original 8 image has a specific resolution, for example 7 if it was created by the reading of an image 6 file.
In this case you have to apply the 5 resolution of the original image to the 4 scaling factors:
Image* img = new Bitmap((int) newWidth, (int) newHeight);
horizontalScalingFactor *= originalBitmap->GetHorizontalResolution() / img->GetHorizontalResolution();
verticalScalingFactor *= originalBitmap->GetVerticalResolution() / img->GetVerticalResolution();
(note: the default resolution 3 for a new Bitmap seems to be 96 ppi, at least 2 on my computer)
or more simply you can change 1 the resolution of the new image:
Image* img = new Bitmap((int) newWidth, (int) newHeight);
img->SetResolution(originalBitmap->GetHorizontalResolution(), originalBitmap->GetVerticalResolution());
http://msdn.microsoft.com/en-us/library/e06tc8a5.aspx
Bitmap myBitmap = new Bitmap("Spiral.png");
Rectangle expansionRectangle = new Rectangle(135, 10,
myBitmap.Width, myBitmap.Height);
Rectangle compressionRectangle = new Rectangle(300, 10,
myBitmap.Width / 2, myBitmap.Height / 2);
myGraphics.DrawImage(myBitmap, 10, 10);
myGraphics.DrawImage(myBitmap, expansionRectangle);
myGraphics.DrawImage(myBitmap, compressionRectangle);
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