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Digital Image Processing 數位影像處理

Digital Image Processing 數位影像處理. 江政杰. What’s An Image. 數位影像. Unit: Pixel. Image Type. Gray 灰階影像. Color 彩色影像. 800x600=480000 pixels. 每個 pixel 是由三個値組成 (R, G, B). 每個 pixel 是由一個値組成. Gray Image. Image I 可以表示成. or. double *Image=NULL;

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Digital Image Processing 數位影像處理

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  1. Digital Image Processing數位影像處理 江政杰

  2. What’s An Image 數位影像 Unit: Pixel

  3. Image Type • Gray 灰階影像 • Color 彩色影像 800x600=480000 pixels 每個pixel是由三個値組成 (R, G, B) 每個pixel是由一個値組成

  4. Gray Image Image I可以表示成 or double *Image=NULL; Image = (double *) malloc(width * height * sizeof(double)); // read a gray image file for (i = 0 ; i < height ; i++ ) for (j = 0 ; j < width ; j++){ fscanf(fpin, "%c", &pixel); *(Image+i*width+j)=(double)pixel; //the pixel at (i, j) }

  5. Color Image Image I可以表示成 or double *Image=NULL; Image = (double *) malloc(width * height * sizeof(double)*3); // read a gray image file for (i = 0 ; i < height ; i++ ) for (j = 0 ; j < width ; j++){ fscanf(fpin, "%c", &pixel); *(Image+i*width+j)=(double)pixel; //R at pixel (i, j) fscanf(fpin, "%c", &pixel); *(Image+i*width+j+1)=(double)pixel; //G at pixel (i, j) fscanf(fpin, "%c", &pixel); *(Image+i*width+j+2)=(double)pixel; //B at pixel (i, j) }

  6. Image Features • Feature: 特徵 影像的pixel一般都非常多, 我們要在其中找到可以代表不同影像的特徵 • 目前常見的影像特徵種類很多, 可分成 • Color: 以顏色為主 • Texture: 以材質為主 • Shape: 以形狀為主 • …

  7. Pixel Feature • 最簡單的特徵取法就是 把所有pixel排列出來 這種方式只適合在小的影像, 例如一個icon是32x32=1024 pixels目前在face detection上很多就是用pixel feature直接表示影像特徵

  8. Color Histogram pixel數量 0 255 亮度值 histogram 是最常用也是最簡單的影像特徵表示法 histogram 是一種統計的方式表示顏色變化與分佈狀況 以上面的例子看, color histogram會轉換成256維度的向量 在color image, 可以針對R, G, B 分別算histogram

  9. Color Moments • 因為color histogram的維度一般都很高, 所以用統計的計量再予以精簡 這480000個値可以計算其平均數與變異數, 用這兩個統計量代表一張影像 • Color Image • R, G, B channels, 各有平均數與變異數 • 共六個値代表, 所以是6維的向量

  10. OpenCV Setup in VC • Library: project->setting->link • cv.lib cvaux.lib highgui.lib cxcore.lib • Directories • Include • C:\PROGRAM FILES\OPENCV\CV\INCLUDE • C:\PROGRAM FILES\OPENCV\CVAUX\INCLUDE • C:\PROGRAM FILES\OPENCV\OTHERLIBS\HIGHGUI • C:\PROGRAM FILES\OPENCV\CXCORE\INCLUDE • Library • C:\PROGRAM FILES\OPENCV\LIB • FilePathName • C:\PROGRAM FILES\OPENCV\bin • Include in programs • #include "cv.h“, "cvaux.h“, "highgui.h“, "cxcore.h"

  11. #include <stdio.h> #include <cxcore.h> #include <highgui.h> #include <math.h> int main( int argc, char** argv ) { CvPoint center; double scale=-3; IplImage* image = cvLoadImage("Beach 2.jpg"); if(!image) return -1; /* 這一段程式將每個pixel逐一調整成整張圖有漸層 center = cvPoint(image->width/2,image->height/2); for(int i=0;i<image->height;i++) for(int j=0;j<image->width;j++) { double dx=(double)(j-center.x)/center.x; double dy=(double)(i-center.y)/center.y; double weight=exp((dx*dx+dy*dy)*scale); uchar* ptr = &CV_IMAGE_ELEM(image,uchar,i,j*3); ptr[0] = cvRound(ptr[0]*weight); ptr[1] = cvRound(ptr[1]*weight); ptr[2] = cvRound(ptr[2]*weight); } cvSaveImage("copy.png", image ); */ cvNamedWindow("test", 1 ); cvShowImage("test", image ); cvWaitKey(); return 0; } Including files 主程式開始 OpenCV內定的資料型態 可以直接用 讀取jpeg檔, 內定函數, 輸入參數是字串 產生一個新的視窗 將影像顯示在視窗內 等待按任一鍵

  12. 工 作 • 熟悉Visual C++ (or VC .net) • 將OpenCV安裝到可以執行 • 程式: 輸入一張影像, 然後秀出這張影像 • 研讀face detection與影片處理的相關資訊

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