Rescale an image

Question

I am trying to rescale on image by down by a factor of 10 and save it

System.Drawing.Bitmap bmi     
var scaleWidth = (int)(bmi.Width * 0.1);
var scaleHeight = (int)(bmi.Height * 0.1);
Rectangle f = new Rectangle(0, 0, scaleWidth, scaleHeight);
Graphics graph = Graphics.FromImage(bmi);           
graph.DrawImage(bmi, new Rectangle(
    ((int)scaleWidth - scaleWidth) / 2, 
    ((int)scaleHeight - scaleHeight) / 2, 
    scaleWidth, scaleHeight));
string a = "a.jpg";
bmi.Save(a);

but when I do this it saves the scaled image, drawn on the original image and I am unsure of how to correct this

Answer 1

You should copy the original bitmap to a new bitmap, scaling as you go. Example (untested):

Bitmap bmpOriginal = /* load your file here */
var scaleWidth = (int)(bmi.Width * 0.1);
var scaleHeight = (int)(bmi.Height * 0.1);
Bitmap bmpScaled = new Bitmap(scaleWidth, scaleHeight);
Graphics graph = Graphics.FromImage(bmpScaled );           
graph.DrawImage(bmpOriginal, new Rectangle(0, 0, scaleWidth, scaleHeight);
bmpScaled.Save("scaledImage.bmp");

Edit: I just noticed this constructor on the Bitmap class, which allows you to simplify your code to this:

Bitmap bmpOriginal = /* load your file here */
var scaleWidth = (int)(bmi.Width * 0.1);
var scaleHeight = (int)(bmi.Height * 0.1);
Bitmap bmpScaled = new Bitmap(bmpOriginal, new Size(scaleWidth, scaleHeight));
bmpScaled.Save("scaledImage.bmp");