Introduction to Emgu
EE4H, M.Sc 04 24086
Computer Vision
Dr. Mike Spann
m.spann@bham.ac.uk
http://www.eee.bham.ac.uk/spannm
About Emgu
 All of this material is taken from an Emgu wiki tutorial
 http://www.emgu.com/wiki/index.php/Tutorial
 Also check out the API documentation
 http://www.emgu.com/wiki/files/2.4.2/document/In
dex.html
 Emgu is a cross platform .NET wrapper to the OpenCV
image processing library
 Written entirely in C# but Allowing OpenCV functions
to be called from .NET compatible languages such as
C#, VB, VC++, IronPython
Setting up Emgu – C#
 There is a nice wiki article about how to set up Emgu
using C#
 http://www.emgu.com/wiki/index.php/Setting_up_EM
GU_C_Sharp
 Also the article presents a tutorial on writing a simple
Emgu application
Emgu to OpenCV mapping
 Can easily map from Emgu to OpenCV
 Function mapping

Emgu.CV.CvInvoke
 Structure mapping

Emgu.CV.Structure.Mxxx
 Enumeration mapping

Emgu.CV.CvEnum
 Example:

IntPtr image = CvInvoke.cvLoadImage("myImage.jpg",
LOAD_IMAGE_TYPE.CV_LOAD_IMAGE_GRAYSCALE);
Emgu to OpenCV mapping
 Emgu also borrows some existing structures in .NET to
represent structures in OpenCV:
.NET Structure
OpenCV structure
System.Drawing.Point
CvPoint
System.Drawing.PointF
CvPoint2D32f
System.Drawing.Size
CvSize
System.Drawing.Rectangle
CvRect
Image representation in Emgu
 Normal to create an image using the genric class
Image<TColor, TDepth> object instead of using
CvInvoke.cvCreateImage()
 Several advantages of this
 Memory is automatically released by the garbage
collector
 Image<TColor, TDepth > class can be examined by
debugger
 Image<TColor, TDepth > class contains advanced
methods that is not available on OpenCV such as
conversion to bitmaps
Image representation in Emgu
 Can create an un-initialized graylevel image of a given
size
Image<Gray, Byte> img1 = new Image<Gray, Byte>(400, 300);
 Or can initialize the pixel data
Image<Gray, Byte> img2 = new Image<Gray, Byte>(400, 300, new Gray(30));
 Similarly for an RGB image
Image<Bgr, Byte> img3 = new Image<Bgr, Byte>(400,300, new Bgr(100, 100, 100));
Image representation in Emgu
 Images can also created from a file or a bitmap
Image<Bgr, Byte> img1 = new Image<Bgr, Byte>("MyImage.jpg");
Image<Bgr, Byte> img3 = new Image<Bgr, Byte>(bmp);
Getting or Setting Pixels in Emgu
 The slow way is to use the [] operator on the image object
// Get the gray level
Gray g = img[y, x];
// Set the gray level
img[y,x] = new Gray(100);
 Faster way is to use the Data property of the image object
Byte g = img.Data[y, x, 0];
 http://stackoverflow.com/questions/5101986/iterate-over-
pixels-of-an-image-with-emgu-cv gives some benchmarking
for iterating over pixel data
Displaying, drawing and
converting images
 An image can be displayed using the ImageBox
control
 ImageBox is a high performance control for displaying
images.

Displays a Bitmap that shares memory with the Image object,
therefore no memory copy is needed (very fast).
 The Image class has a ToBitmap() function that return
a Bitmap object
 Allows the image to be displayed on a PictureBox control
 There is also an ImageViewer class in the Emgu.CV.UI
namespace
Displaying, drawing and converting
images
 The Draw() method in Image< Color,Depth> can be
used to draw different types of objects, including fonts,
lines, circles, rectangles, boxes, ellipses as well as
contours
Image<Gray, Byte> image = new Image<Gray, Byte>(400, 300);
Rectangle rect =new Rectangle(0,0,200,300);
image.Draw(rect, new Gray(200), 2);
 More efficient method is to draw as a graphics overlay
Image<Gray, Byte> image = new Image<Gray, Byte>(400, 300);
Rectangle rect =new Rectangle(0,0,200,300);
Graphics.FromImage(image). DrawRectangle(new Pen(yellow), rect);
Conclusions

Emgu is a powerful development platform for image
processing/computer vision

Similar capabilities to OpenCV but has additional
capabilities because of additional language features
specific to C#