C# winforms: graphics.DrawImage issue

Question

I have a really strange problem with Graphics.DrawImage method.

I have the PictureBox control in the Panel control with AllowScroll property = true. The program cuts the image on small parts basing on the area selected by the user.

I load the image 300x547 and select the area (the red rectangle):

program properly cuts the image:

then, I load another image 427x640:

alt text http://img34.imageshack.us/img34/7950/56727000.png

and then, as the result I see that the image is not cut properly. Each img.jpg file has properly width & height but the drawn image is too small:

here's the code snippet - it saves the bitmap area selected by the user:

  Image OriginalIMG= (Image)((PictureBox)panel1.Controls["picBox"]).Image.Clone()
  Bitmap bmp = new Bitmap(selectedAreaRECT.Width, selectedAreaRECT.Height);
  Graphics g = Graphics.FromImage(bmp);

  g.DrawImage(OriginalIMG, 0,0, selectedAreaRECT, GraphicsUnit.Pixel);
  g.Save();
  g.Dispose();

  bmp.Save(AppDomain.CurrentDomain.BaseDirectory + @"\Temp\" + "img1.jpg", System.Drawing.Imaging.ImageFormat.Jpeg);

As You see, the code is the same for the img1.jpg from image A and from Image B. I'm trying to resolve that stupid problem for too long, I don't know what's the reason of that problem. I tried different overloads of the DrawImage method, with no success

EDIT

Resolved! the dafault DPI value of the System.Drawing.Bitmap is = 96, if I open an image with DPI != 96 then the problem described above occurs. To get rid of it, I needed to use SetResolution method:

Bitmap result = new Bitmap(width, height);
result.SetResolution(OriginalIMG.HorizontalResolution, OriginalIMG.VerticalResolution);

that resolves the problem :) Thanks for everyone for help ! :)

Do You mean HorizontalResolution and VerticalResolution ? they're = 96 — Tony
– Tony, Commented Apr 21, 2010 at 10:20
I think the DPI will resolve the problem, image A has DPI = 96, image B has DPI = 150, I'll check it :) — Tony
– Tony, Commented Apr 21, 2010 at 10:34

Dan Byström · Accepted Answer · 2010-04-21 11:05:35Z

5

I'd try: (edited)

  g.DrawImage(
    OriginalIMG,
    new Rectangle( Point.Empty, bmp.Size ),
    selectedAreaRECT.X, selectedAreaRECT.Y,
    selectedAreaRECT.Width, selectedAreaRECT.Height, 
    GraphicsUnit.Pixel);

to see if it makes a difference.

Although it has nothing to do with your problem: you're forgetting to .Dispose() some things, and I'm not sure why you have to .Clone() the image.

edited Apr 21, 2010 at 11:05

answered Apr 21, 2010 at 10:28

Dan Byström

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1 Comment

Tony Over a year ago

there is no constructor like Yours

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