c# - How can I capture as bitmap only what a picturebox is displaying, without using "copy from screen"?

Question

Specifically: I need to capture as a bitmap a specific region of what a picturebox is actually displaying. The coordinates of the region are specified by the bounds of a control that I have overlayed on top of the picturebox (but that belongs to the picturebox). The control is hidden when I make the "snapshot" of the region.

I tried using normal screen capture methods (CopyFromScreen), but you can't really control the timing there. So it was capturing "interstitial" states, like transitions between photos in my picturebox. Frequently it was only capturing purely black images (the background color of the picture box).

So I tried just converting the image (picturebox.image property) being displayed to a bitmap. The problem there is that the picture box is rarely showing exactly the image. It's displaying some PORTION of the image, scaled and clipped as appropriate to it's sizemode (which is zoom). So the I can't just take my control coordinates and clip them from the image as a whole.

So I tried to estimate what portion of the image was being displayed, and correcting my rectangle based on that. Turns out that I was basically re-creating the "zoom" code of the picturebox to do this (using aspect ratio of the picturebox, the aspect ratio of the image, guessing at what level of scaling is currently happening to the image if it's larger or smaller than the picturebox, etc). It was not pretty.

So: now I need a method of just capturing only the bitmap currently being displayed in the client area of the picturebox, including the photo and any black "letterboxing" currently being displayed around it. Anybody got one?

Remember that I can't rely on using CopyFromScreen. It's not reliable enough for my purposes. I think I need a method of getting picturebox to TELL me the bits it is displaying.

Answer 1

This will copy and save the currently shown content of the PictureBox including a BackgroundImage (if there is one and if it shines through) and also all Controls that belong to the PictureBox, like Labels etc.. Also included are elements drawn in the Paint event. Things drawn outside the Paint event are non-persistent and will not be included.

using (Bitmap bmp = new Bitmap(pictureBox1.ClientSize.Width,
                               pictureBox1.ClientSize.Height))
{
   pictureBox1.DrawToBitmap(bmp, pictureBox1.ClientRectangle);
   bmp.Save(yourfilename, ImageFormat.Png);
}

Note: On my test Form the PicureBox is sitting inside an AutoScroll Panel pan_PBscroll. The PictureBox is displaying pixels 1:1 and is therefore, with a photograph loaded, much bigger than the Panel, the Form or even the Screen. So to clip to the actually visible parts I could not use the pictureBox1.ClientSize and pictureBox1.ClientRectangle but used the dimensions of that Panel. This may well apply to you, too.

I'm not sure about your timing issues. But since you mentioned CopyFromScreen here are a few differences:

• CopyFromScreen makes a 1:1 copy of each screen pixel
• This includes non-persistent drawings and excludes anything covered or hidden
• Control.DrawToBitmap makes the Control draw itself onto a Bitmap, just as it draws itself during Paint
• This excludes anything that doesn't belong to the Control but includes all members of its Controls collection
• This also excludes non-persistent drawings but includes the full Size of the Control, whether it fits on the Form or Screen or not and whether it is hidden or covered or not.
• For Controls with active Scrollbars only the visible parts are copied. To copy all you need to resize it temporarily. Then you can get a complete image of a listbox even if it has a thousand items..