Develop Reference

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

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.

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..

Since you're using a PictureBox I would say to take a look PictureBox.Image where you can get the Bitmap object.
Hope it helps.

Resize an image in a PictureBox to as large as it can go, while maintaining aspect ratio?

I'm trying to make it so that an image in a PictureBox control will adjust its size automatically depending on the size of the window, but maintain the aspect ratio. So far just setting SizeMode to StretchImage causes the image to stretch to fit the entire PictureBox control. This ignores the aspect ratio, which isn't what I want.
Is it possible to maintain the aspect ratio, but still stretch the image to the largest it can go dynamically as the form's size changes? Is it possible to do this and have it still be centered? I imagine I could recreate the image in memory each time the window is resized, but this seems like a bad idea.

I believe that this is the effect of PictureBoxSizeMode.Zoom. The documentation says that:
The size of the image is increased or decreased maintaining the size ratio.
You set this on the PictureBox.SizeMode property. The "Remarks" section of the documentation for that function also says:
Using the Zoom value causes the image to be stretched or shrunk to fit the PictureBox; however, the aspect ratio in the original is maintained.
You can, of course, set the PictureBox.SizeMode property either in the designer's Properties Window or in code (e.g., in your form's constructor):
myPictureBox.SizeMode = PictureBoxSizeMode.Zoom;
If this doesn't do exactly what you want, you could always implement the resizing logic yourself. Your concern is that recreating the image in memory each time that the control is resized "seems like a bad idea", but I'm not sure why it seems that way to you. The only problem would be if you weren't careful to destroy unused graphics objects, like the old Bitmap. Not only do these objects contain unmanaged resources that need to be freed, you'll start exerting extreme amounts of pressure on memory if you just let them leak.
Alternatively, to avoid creating temporary bitmaps, you can do what the PictureBox control probably does internally and use the Graphics.DrawImage method to handle the stretching. If you pass it a rectangle, it will automatically scale the image to fit inside of the rectangle.

Change the 'SizeMode' to Zoom.
As the name suggests, "StretchImage" will stretch it to fit the image file. Easy process of elimination would have given you the same result.

According to the PictureBoxSizeMode documentation you can specify PictureBoxSizeMode.Zoom to get the image to keep its aspect ratio. It will zoom as big as possible without any part of the image overflowing the picture box.
And you can play with the Dock property (setting DockStyle.Fill) to get the picture box to resize to the size of its container.

You can add it to a Web Browser control. Using Ctrl and mouse button you can zoom in as much as you like.

C# Image over another image

I have a picturebox with a fixed sized image (256x256) generated by the program. I have another smaller image as a resource. What I want to do is when my cursor is over the image and I hold down the mouse button, the smaller image "anchors" with the mouse pointer so it moves around with it. If I let go of the mouse button, the smaller image will stay in that position on top of the bigger image. The smaller image is basically a marker, something like an X or O.
I was thinking of having a second picturebox on top of the first picturebox but I can't make it transparent. Or redrawing the image with the smaller image on top of it and reloading the image into the picturebox, but I'm not sure how to do that and I think it's going to be pretty slow redrawing it each time I move the mouse.
So how can I have a marker image move around on top of a bigger image and have it stay there?

Create your control for this instead of using PictureBox. PictureBox should be used ONLY for fixed images on the form, nothing else.
Instead, derive your control from UserControl. Turn on double buffering for it. In OnPaint method, first draw your background picture, then your marker picture after it. Don't worry, it WON'T be slow and it WILL work as it should.
When you release the mouse, update background picture by drawing your marker picture on it.
Since every sentence here is a little discovery by itself, hope you'll have a good time coding your little game :)

Paint in A Grid And Export Image? (Windows or Mac)

I want the user to be able to paint in a grid in my Windows application 16x16 pixels large. Of course these are visiably bigger when editing but then can be output as a png file at its actual 16x16 size.
Im not asking for a full solution of course but if you could point me in the right direction for what to use to build up the grid which will allow me paint colours into it and then output it.
Any help much appreciated, thanks.

here is a somewhat general idea:
depending on the application, i'd use a simple picturebox, load a bitmap (from file, db, create empty, ...) and handle mouse clicks on that ...
translate the screen coordinates to your 16x16 matrix, and use some "needle-scheme" to interact with that image (means you have some sort of colorpicker that selects the color to use, and a click on a pixel sets it to that color)
since your image is only 16x16 you will probably want to set the picturebox to stretch or zoom mode
output of an image object is rather simple if you make use of the System.Drawing.Image class
if you need further details/help, let me know...

Convert screen coordinates to picture coordinates

I have the following problem: A program displays a picture using a PictureBox. The picture contains two rectangles A and B that are drawn after the image is loaded.
The image inside the picture box is zoomed and the rectangles A and B are painted using the Graphics object of the loaded image. Is there a simple method to determinate if a user clicked the area inside these rectangles e.g. converting screen coordinates to picture coordinates.
Edit: No longer relevant, found another solution.
Edit 2: My solution was to use two picture boxes at the A and B location instead of modifying the image directly. It has some minor disadvantages specific to my solution, but I had to finish the project in time

This SO post discusses the zoom factor of a picture box and that you cannot determine it.
Therefore I think, without getting the zoom factor, you may not be able to calculate the position.