Alireza Shirani
Researcher of Medical Image and Signal Processing
M.S Electrical Engineering shiranialireza@yahoo.com
Spring 1392

• Introduction of OpenCV
• How to Install OpenCV
• Read & Write image & other related Function
• Read & Write video & other related Function

Introduction of OpenCV
 OpenCv (open computer vision ) library is library of programming function mainly aimed at real time computer vision
 developed by Intel and now supported by Willow Garage.
 It’s free for use under the open source BSD License
 OS Support:
Windows ,Android ,Blackberry ,Linux Distribution such as puppy, Ubuntu,…,Maemo ,Free BSD,…
 Programming language
OpenCv written in C++ and its primary interface is in
C++.There are full interfacing Python, Java ,MATLAB
 OpenCV can be used in Embedded Systems.

Read & Write image & other related Function
 Load Image: cvLoadImage
 The function cvLoadImage loads an image from the specified file and returns the pointer to the loaded image
 IplImage* cvLoadImage(const char* filename, Parameters)
• Currently the following file formats are supported:
 Windows bitmaps - BMP, DIB
 JPEG files - JPEG, JPG, JPE
 Portable Network Graphics - PNG
 Portable image format - PBM, PGM, PPM
 Sun rasters - SR, RAS
 TIFF files - TIFF, TIF o Parameters : o CV_LOAD_IMAGE_COLOR the loaded image is forced to be a 3-channel color image o CV_LOAD_IMAGE_GRAYSCALE the loaded image is forced to be grayscale o CV_LOAD_IMAGE_UNCHANGED the loaded image will be loaded as is.

Read & Write image & other related Function
IplImage is structure that contain all details about Image that was loaded

Read & Write image & other related Function
 Open window cvNamedWindow
 cvNamedWindow(const char* name, int flags) ¶
The function cvNamedWindow creates a window which can be used as a placeholder for images name – Name of the window in the window caption that may be used as a window identifier.
flags – Flags of the window. Currently the only supported flag is
CV_WINDOW_AUTOSIZE
 Delay in milliseconds cvWaitKey
 Int cvWaitKey(int delay=0)
The function cvWaitKey waits for key event infinitely ( delay<=0) or for delay milliseconds. Returns the code of the pressed key or -1 if no key was pressed before the specified time had elapsed

Read & Write image & other related Function
 Release Space of RAM cvReleaseImage
 void cvReleaseImage(IplImage* image)
 Deallocates the image header and the image data
• image – Double pointer to the image header

Read & Write image & other related Function

 IplImage* cvCreateImage(CvSize size, int depth, int channels)

• size – Image width and height
• depth – Bit depth of image elements.
• channels – Number of channels per pixel

 2D point with integer coordinates

Read & Write image & other related Function
 MoveWindoe cvMoveWindow(*name,x,y)
 cvMoveWindow(const char* name, int x, int y)
• The function cvMoveWindow() changes the position of the window o x – New x coordinate of the top-left corner o y – New y coordinate of the top-left corner
 Convert Image cvConvertImage
 cvConvertImage(const CvArr* src, CvArr* dst, int flags=0)
• Converts one image to another with an optional vertical flip
• src – Source image dst – Destination image
• The operation flags:
• CV_CVTIMG_FLIP - Flips the image vertically
• CV_CVTIMG_SWAP_RB - Swaps the red and blue channels. In OpenCV color images have BGR channel order, however on some systems the order needs to be reversed before displaying the image.

Read & Write image & other related Function
 Font setting in opencv cvInitFont
 cvInitFont(CvFont* font, int fontFace, double hscale, double vscale, double shear=0, int thickness=1, int lineType=8)
 The function initializes the font structure that can be passed to text rendering functions
 font – Pointer to the font structure initialized by the function
• fontFace :
• CV_FONT_HERSHEY_SIMPLEX - normal size sans-serif font
• CV_FONT_HERSHEY_PLAIN - small size sans-serif font
• CV_FONT_HERSHEY_DUPLEX - normal size sans-serif font (more complex than
 Hscale : Horizontal scale
 Vscale: Vertical scale
 param thickness : Thickness of the text strokes
 param shear: Approximate tangent of the character slope relative to the vertical line. A zero value means a non-italic font. 1.0f means about a 45 degree slope, etc.
 lineType : The function initializes the font structure that can be passed to text rendering functions.

Read & Write image & other related Function

 void cvPutText(CvArr* img, const char* text, CvPoint org, const
CvFont* font, CvScalar color)
 The function renders the text in the image with the specified font and color
• img – Input image
• text – String to print
• org – Coordinates of the bottom-left corner of the first letter
• font – Pointer to the font structure
• color – Text color
 CvScaler: is structure that contain R,G,B values of Pixels
 Example CV_RGB(255,255,255) create white color

Read & Write image & other related Function

 IplImage* cvCreateImage(CvSize size, int depth, int channels)
 Creates an image header and allocates the image data
• size – Image width and height
• depth – Bit depth of image elements.
• channels – Number of channels per pixel.

Read & Write image & other related Function
 Implements the Canny Algorithm cvCanny
 void cvCanny(const CvArr* image, CvArr * edges, double threshold1, double threshold2, int aperture_size=3)
 The function finds the edges on the input image and marks them in the output image edges using the Canny algorithm.
• image – Single-channel input image
• edges – Single-channel image to store the edges found by the function
• threshold1 – The first threshold
• threshold2 – The second threshold
• aperture_size – Aperture parameter for the Sobel operator

Read & Write image & other related Function

 cvLine(CvArr* img, CvPoint pt1, CvPoint pt2, CvScalar color, int thickness=1, int lineType=8, int shift=0)
 The function draws the line segment between pt1 and pt2 points in the image
• img – The image
• pt1 – First point of the line segment
• pt2 – Second point of the line segment
• color – Line color
• thickness – Line thickness
• lineType – Type of the line:
• 8 - (or omitted) 8-connected line.
• 4 - 4-connected line.
• CV_AA - antialiased line.
• shift – Number of fractional bits in the point coordinates

Read & Write image & other related Function

 cvCircle(CvArr* img, CvPoint center, int radius, CvScalar color, int thickness=1, int lineType=8, int shift=0)
 The function draws a simple or filled circle with a given center and radius.
• img – Image where the circle is drawn
• center – Center of the circle
• radius – Radius of the circle
• color – Circle color
• thickness – Thickness of the circle outline if positive, otherwise this indicates that a filled circle is to be drawn
• lineType – Type of the circle boundary
• shift – Number of fractional bits in the center coordinates and radius value

Read & Write image & other related Function
 Smooth cvSmooth
 cvSmooth(const CvArr* src, CvArr* dst, int smoothtype=CV_GAUSSIAN, int param1=3, int param2=0, double param3=0, double param4=0)
 Function smooths an image using one of several methods.
• src – The source image
• dst – The destination image
• smoothtype – Type of the smoothing:
• CV_BLUR_NO_SCALE linear convolution with box kernel (all 1’s). If you want to smooth different pixels with different-size box kernels, you can use the integral image that is computed using Integral
• CV_BLUR linear convolution with box kernel (all 1’s) with subsequent scaling by
• CV_GAUSSIAN linear convolution with a Gaussian kernel
• CV_MEDIAN median filter with a square aperture
• CV_BILATERAL bilateral filter with a square aperture

Read & Write image & other related Function

 int cvSaveImage(const char* filename, const CvArr* image)
 The function cvSaveImagesaves the image to the specified file
• filename – Name of the file.
• image – Image to be saved

Read & Write video & other related
Function
 capturing a video from a camera
 The functioncvCaptureFromCAMallocates and initializes the
CvCapture structure for reading a video stream from the camera
 CvCapture* cvCaptureFromCAM(int index)
 index – Index of the camera to be used

Read & Write video & other related
Function
 Extract frame from camera cvQueryFrame
 Grabs and returns a frame from a camera or file
 IplImage* cvQueryFrame(CvCapture* capture)
 capture – video capturing structure

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