Introduction of OpenCV

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

2. Outline Of Talking • Introduction of OpenCV • How to Install OpenCV • Read & Write image & other related Function • Read & Write video & other related Function

3. 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.

4. 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 • Parameters : • CV_LOAD_IMAGE_COLOR the loaded image is forced to be a 3-channel color image • CV_LOAD_IMAGE_GRAYSCALE the loaded image is forced to be grayscale • CV_LOAD_IMAGE_UNCHANGED the loaded image will be loaded as is.

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

6. 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

7. 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

8. Read & Write image & other related Function • Create image cvCreateImage • 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 • Point of image CvPoint • 2D point with integer coordinates

9. 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 • x – New x coordinate of the top-left corner • 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.

10. 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.

11. Read & Write image & other related Function • Write string on OpenCV cvPutText • 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

12. Read & Write image & other related Function • Convert Image cvCreateImage • 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.

13. 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

14. Read & Write image & other related Function • Draws a line cvLine • 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

15. Read & Write image & other related Function • Draw circle cvCircle • 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

16. 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

17. Read & Write image & other related Function • Save Image cvSaveImage • 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

18. Read & Write video & other related Function • capturing a video from a camera cvCaptureFromCAM • 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

19. 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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