Using System.Drawing to make a selection tool, and cropping an image in vb.net

Question

If i wanted to crop an image in VB.net, how would I go about doing it? I am trying to let the user drag out the box they want (system.drawing.rectangle), and it will automatically remove the edges surrounding the box.

My first problem is primarily the fact that I cannot make the system.drawing.rectangle visible. It is not displaying at all, I am setting its location and height programmatically, but nothing is showing up. I know there is probably something fairly obvious I am missing...but I cannot seem to find it.

My larger issue, however, lies with the cropping itself. I cannot find any crop methods, at all. Is there a hidden one I am missing? Or must I code it myself? How would I go about doing this? It ought to be able to output to a bitmap image object.

Thanks for the help, I am surprised this hasn't been asked on here before....

Answer 1

Regarding your first problem: a Rectangle isn't by itself visible. You have to draw it on your canvas using the Graphics object's DrawRectangle(...) method. For drawing a selection tool, you'll want to set your Pen object's DashCap and DashPattern properties.

To "crop" an image, you basically want to take the portion of a larger image delineated by a smaller Rectangle, and turn it into a new Bitmap. This can be done using one of the 30 overloads of the Graphics object's DrawImage(...) method. You can either keep the cropped portion in its original dimensions (resulting in a smaller Bitmap than your original), or you can "blow it up" to something like the original image's size. If you do the latter approach, it is usually a good idea to set your Graphics object's InterpolationMode property to HighQualityBicubic (I think that's the one, anyway), since the default InterpolationMode is pretty crappy.

There are a number of different ways of rendering images in .Net - it might help if you posted some of your code, along with an explanation of the exact problems you're running into.

Here is another answer with a link to a sample app (and source code in C#, sorry) that may help you get started.

Answer 2

There are a number of articles on these topics on CodeProject:

Pick your favorite flavor (though I encourage you to check out the C# projects - it shouldn't be too hard to convert).

VB
Image Cropping with Image Resizing Using vb.net

C#
Cropping Images An Easy to Use Image Resizing and Cropping Control
Image Processing using C# (see the Cropping section - I was able to use this code in one of my projects)

WPF/C#
WPF Interactive Image Cropping Control
A Photoshop-like Cropping Adorner for WPF