A Not-So-Simple Transformation

← 左為cvPyrDown()兩次的結果，
　 右為cvCanny()一次的結果。

// Example 2-5. Using cvPyrDown() to create a new image that is half the width and height of the input image
// Example 2-6. The Canny edge detector writes its output to a single channel (grayscale) image
// Example 2-7. Combining the pyramid down operator (twice) and the Canny subroutine in a simple image pipeline
// Example 2-8. Simplifying the image pipeline of Example 2-7 by making the individual stages release their intermediate memory allocations

#include "highgui.h"
#include "cv.h"

IplImage *doPyrDown( IplImage * , int );
IplImage *doCanny( IplImage * , double , double , double );

int main( int argc , char **argv )
{
　cvNamedWindow( "Input" , CV_WINDOW_AUTOSIZE );
　cvNamedWindow( "Output1" , CV_WINDOW_AUTOSIZE );
　//cvNamedWindow( "Output2" , CV_WINDOW_AUTOSIZE );
　//cvNamedWindow( "Output3" , CV_WINDOW_AUTOSIZE );

　IplImage *image = cvLoadImage( argv[1] , 0);
　IplImage *out1 = doPyrDown( image , IPL_GAUSSIAN_5x5 );
　//IplImage *out2 = doPyrDown( out1 , IPL_GAUSSIAN_5x5 );
　//IplImage *out3 = doCanny( out2 , 10 , 100 , 3 );
　out1 = doPyrDown( out1 , IPL_GAUSSIAN_5x5 );
　cvShowImage( "Input" , out1 );
　out1 = doCanny( out1 , 10 , 100 , 3 );

　//cvShowImage( "Input" , image );
　cvShowImage( "Output1" , out1 );
　//cvShowImage( "Output2" , out2 );
　//cvShowImage( "Output3" , out3 );

　cvWaitKey( 0 );

　cvReleaseImage( &image );
　cvReleaseImage( &out1 );
　//cvReleaseImage( &out2 );
　//cvReleaseImage( &out3 );

　cvDestroyWindow( "Input" );
　cvDestroyWindow( "Output1" );
　//cvDestroyWindow( "Output2" );
　//cvDestroyWindow( "Output3" );
　return 0;
}

// Example 2-5.
IplImage *doPyrDown( IplImage *in , int filter )
{
　// Best to make sure input image is divisible by two.
　//
　assert( in->width%2 == 0 && in->height%2 == 0 );

　IplImage *out = cvCreateImage( cvSize( in->width/2 , in->height/2 ) , in->depth , in->nChannels );
　cvPyrDown( in , out , filter );
　return out;
}

// Example 2-6.
IplImage *doCanny( IplImage *in , double lowThresh , double highThresh , double aperture )
{
　if( in->nChannels != 1 )
　　return 0;　// Canny only handles gray scale iamges

　IplImage *out = cvCreateImage( cvGetSize( in ) , IPL_DEPTH_8U , 1 );
　cvCanny( in , out , lowThresh , highThresh , aperture );
　return out;
}