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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.

PictureBox BackgroundImage property doesn't work

I've set the backgroundImage property, and still the image covers all the UI, what am I doing wrong?
Thank you.

You're not providing enough information, but possible scenarios are:
The PictureBox is set to cover the entire form
You've not set the PictureBox's BackgroundImage property but the one of the form itself
You have set the PictureBox to stretch the image (goes together with 1.)
Why are you setting BackgroundImage at all? Usually you put a PictureBox on the form, assign the image and make sure that it has the appropriate size (or stretches, which I assume your's is doing). Usually you don't need the BackgroundImage property to display an image in the PictureBox.

Yes, Image and BackgroundImage, both of them
I assume you've set the BackgroundImage for the form and are now trying to clear the BackgroundImage of the PictureBox, that's why the "Clear" button is grayed out and that's why you see both of them.
Go ahead and select the form first by clicking somewhere on it where there is no other control, and then go to the BackgroundImage property and clear it.

Resizing the form elements on resizing the form

how to Resizing the Windows form elements on resizing the form? is there any way to set the width of picturebox, panel, etc 100% like CSS? suggest me some help for best practices of layout? When i resize the Windows form, I want that Image size also change when i resize the image. like Windows Picture Viewer

You would probably be okay with the Anchor property of the controls.
http://msdn.microsoft.com/en-us/library/system.windows.forms.control.anchor(v=vs.71).aspx

You should look into Control Docking, it'll probably suit your needs.

What you may want is to set the properties of the image control to fill the image inside.
Steps:
I created a new windows form
I added a picture box to the form
I set the picture box "Dock" property to "Fill"
I added an image to the picture box
I set the SizeMode property to "StretchImage" ("Zoom" might better fit your needs")

how do I set images to scale to 100% of their table-cell? (C#/WinForms)

I have the TableLayoutControl anchored to scale with the window and the images in it need to scale with them. I am not concerned with image quality.

Assuming this is WinForms and you have a bunch of PictureBoxes in cells of a TableLayoutPanel, set each one's Dock to Fill and SizeMode to StretchImage.

Why isn't PictureBox.Image autoscaling to fit in?

I've an interface where user selects picture (using OpenFileDialog) and its shown in a fixed size picturebox. I want this picture to fit in the picturebox even if the resolution is high.
What property do I need to set inorder to let my image AutoScaleToFitIn the PicutreBox?

You could set the PictureBox.SizeMode property to StretchImage.

Look at the SizeMode property