OpenCV - 縮小圖像

#include <stdio.h>
#include <cv.h>
#include <highgui.h>

int main()
{
    char FileName[10]="rain.jpg";

    // 來源指標
    IplImage *src = 0;

    // 目的指標
    IplImage *dst = 0;

    // 縮小倍數
    float scale = 0.618;

    // 目標圖像的大小
    CvSize dst_cvsize;

    // 載入圖檔
    src = cvLoadImage("rain.jpg",1);

    // 設定目標寬為100 pixel
    dst_cvsize.width = 100;
    // 同比例縮小
    dst_cvsize.height = src->height * ((float) dst_cvsize.width/src->width);

    // 建構目標圖像
    dst = cvCreateImage(dst_cvsize,src->depth,src->nChannels);

    // 縮小來源圖到目標圖像
    cvResize(src,dst,CV_INTER_LINEAR);

    // 列印出原圖與縮小後圖的大小
    printf("the original size is %i\n",src->imageSize);
    printf("the scaled size is %i\n",dst->imageSize);

    cvNamedWindow("src",CV_WINDOW_AUTOSIZE);

    cvNamedWindow("dst",CV_WINDOW_AUTOSIZE);

    // 顯示來源圖像
    cvShowImage("src",src);

    // 顯示目標圖像
    cvShowImage("dst",dst);

    // 等待用戶反應
    cvWaitKey(-1);

    // 釋放來源圖占用的記憶體
    cvReleaseImage(&src);

    // 釋放目標圖占用的記憶體
    cvReleaseImage(&dst);

    return 0;
}

編譯方式：
$ gcc `pkg-config opencv --libs --cflags` main.c -o main

參考資料：
縮放圖片

OpenCV - 如何將IplImage型態的image轉換為unsigned char的形式供後續處理?

// start capturing frames from camera
// 0:autodetect
CvCapture *camera = cvCreateCameraCapture(0);
// 確認camera不為NULL
assert(camera);
IplImage *image = cvQueryFrame(camera);
// 確認camera不會NULL
assert(image);
// 求得image的影像大小資訊
CvSize imgSize;
imgSize = cvGetSize(image);
// 將IplImage型態的 image 轉換為 BYTE的image_rawdata
void *image_rawdata;
cvGetImageRawData( image, ( uchar** )&image_rawdata, 0, &imgSize );
// image 是3個channel (RGB) image_rawdata 的大小為 Height * Width * 3
for(j = 0; j < imgSize.height ; j ++) for(i = 0; i < imgSize.width ; i ++)
{
  // 取得第(i,j) pixel 的 R、G、B值
  B = image_rawdata[(j * imgSize.width + i) * 3 + 2];
  G = image_rawdata[(j * imgSize.width + i) * 3 + 1];
  R = image_rawdata[(j * imgSize.width + i) * 3 + 0];
}

參考資料：
OpenCV DIY手冊

OpenCV相關函式與資料結構

這一個是在opencv上很常用的資料結構

資料結構都放在/usr/include/opencv/cxtypes.h

/****************************************************************************************\
*                                  Image type (IplImage)                                 *
\****************************************************************************************/

#ifndef HAVE_IPL

/*
 * The following definitions (until #endif)
 * is an extract from IPL headers.
 * Copyright (c) 1995 Intel Corporation.
 */
#define IPL_DEPTH_SIGN 0x80000000

#define IPL_DEPTH_1U     1
#define IPL_DEPTH_8U     8
#define IPL_DEPTH_16U   16
#define IPL_DEPTH_32F   32

#define IPL_DEPTH_8S  (IPL_DEPTH_SIGN| 8)
#define IPL_DEPTH_16S (IPL_DEPTH_SIGN|16)
#define IPL_DEPTH_32S (IPL_DEPTH_SIGN|32)

#define IPL_DATA_ORDER_PIXEL  0
#define IPL_DATA_ORDER_PLANE  1

#define IPL_ORIGIN_TL 0
#define IPL_ORIGIN_BL 1

#define IPL_ALIGN_4BYTES   4
#define IPL_ALIGN_8BYTES   8
#define IPL_ALIGN_16BYTES 16
#define IPL_ALIGN_32BYTES 32

#define IPL_ALIGN_DWORD   IPL_ALIGN_4BYTES
#define IPL_ALIGN_QWORD   IPL_ALIGN_8BYTES

#define IPL_BORDER_CONSTANT   0
#define IPL_BORDER_REPLICATE  1
#define IPL_BORDER_REFLECT    2
#define IPL_BORDER_WRAP       3

typedef struct _IplImage
{
    int  nSize;         /* sizeof(IplImage) */
    int  ID;            /* version (=0)*/
    int  nChannels;     /* Most of OpenCV functions support 1,2,3 or 4 channels */
    int  alphaChannel;  /* ignored by OpenCV */
    int  depth;         /* pixel depth in bits: IPL_DEPTH_8U, IPL_DEPTH_8S, IPL_DEPTH_16S,
                           IPL_DEPTH_32S, IPL_DEPTH_32F and IPL_DEPTH_64F are supported */
    char colorModel[4]; /* ignored by OpenCV */
    char channelSeq[4]; /* ditto */
    int  dataOrder;     /* 0 - interleaved color channels, 1 - separate color channels.
                           cvCreateImage can only create interleaved images */
    int  origin;        /* 0 - top-left origin,
                           1 - bottom-left origin (Windows bitmaps style) */
    int  align;         /* Alignment of image rows (4 or 8).
                           OpenCV ignores it and uses widthStep instead */
    int  width;         /* image width in pixels */
    int  height;        /* image height in pixels */
    struct _IplROI *roi;/* image ROI. if NULL, the whole image is selected */
    struct _IplImage *maskROI; /* must be NULL */
    void  *imageId;     /* ditto */
    struct _IplTileInfo *tileInfo; /* ditto */
    int  imageSize;     /* image data size in bytes
                           (==image->height*image->widthStep
                           in case of interleaved data)*/
    char *imageData;  /* pointer to aligned image data */
    int  widthStep;   /* size of aligned image row in bytes */
    int  BorderMode[4]; /* ignored by OpenCV */
    int  BorderConst[4]; /* ditto */
    char *imageDataOrigin; /* pointer to very origin of image data
                              (not necessarily aligned) -
                              needed for correct deallocation */
}
IplImage;

函式都放在/usr/include/opencv/cxcore.h中

/* Returns width and height of array in elements */
(CvSize) cvGetSize( const CvArr* arr );

/usr/include/opencv/highgui.h

/* start capturing frames from camera: index = camera_index + domain_offset (CV_CAP_*) */
(CvCapture*) cvCreateCameraCapture( int index );

/* Returns width and height of array in elements */
CVAPI(CvSize) cvGetSize( const CvArr* arr );

/usr/include/opencv/cxtypes.h
// CvArr就是void
typedef void CvArr;

/* Retrieves raw data of CvMat, IplImage or CvMatND. In the latter case the function raises an error if the array can not be represented as a matrix */
把IplImage轉換成uchar資料陣列
(void) cvGetRawData( const CvArr* arr, uchar** data, int* step CV_DEFAULT(NULL), CvSize* roi_size CV_DEFAULT(NULL));
(void) cvGetImageRawData( const CvArr* arr, uchar** data, int* step CV_DEFAULT(NULL), CvSize* roi_size CV_DEFAULT(NULL));

OpenCV

example01
讀取圖片
main.c

#include <stdio.h>
#include <cv.h>
#include <highgui.h>

int main()
{
    char FileName[10]="rain.jpg";
    IplImage *Image1 = cvLoadImage(FileName,1);
    cvNamedWindow("Show Image",0);
    cvResizeWindow("Show Image",300,400);
    cvShowImage("Show Image",Image1);
    cvWaitKey(0);
    cvDestroyWindow("Show Image");
    cvReleaseImage(&Image1);
}

編譯方式
$ gcc `pkg-config opencv --libs --cflags` main.c -o main

example02
讀取webcam
main.c

#include <cv.h>
#include <highgui.h>
#include <stdio.h>

int main()
{
    CvCapture *capture;
    IplImage *frame;
    capture =cvCaptureFromCAM(0) ;
    cvNamedWindow("Webcam",0);
    while(1)
    {
        frame = cvQueryFrame(capture);
        cvShowImage("Webcam",frame);
        if(cvWaitKey(10)>=0)
        {
              break;
        }
    }
    cvReleaseCapture(&capture);
    cvDestroyWindow("Webcam");
}

編譯方式
$ gcc `pkg-config opencv --libs --cflags` main.c -o main

參考資料：
OpenCV中文網站
HighGUI Reference Manual
opencv教學網頁
HighGUI參考手冊
Introduction to programming with OpenCV

其它資料：
cvGetRawData()的奇怪問題
ArtificialWistom: OpenCV
opencv編程入門4