Introduction
A recent stab at grabbing images from the Flea2 camera using APIs from the FlyCapture2 SDK by Point Gray Research (PGR). Additionally, the camera was to be used in “Format 7 mode”, so that we may grab partial regions of the complete image.
This application builds on the AsynchTriggerEx C++ example provided by PGR, so that the user can grab images from the camera either by way of software triggers, or from an external hardware triggers.
Using Format7 mode to grab partial images
The Format7ImageSettings data structure is modified in order to set the desired output image size, pixel formats etc. Standard FlyCapture API calls are used to perform all necessary camera actions: connect to camera, disconnect from camera, start image capturing, retrieve image buffers etc. When the using the default equipment setup, the input images obtained are grayscales of 24 x 480 pixels consisting of an array of dark gray spots against a lighter shade of gray background.
Converting FlyCapture images into OpenCV images
In the image grabbing loop, FlyCapture2-obtained images are converted into OpenCV-compatible images by copying the pixel data from one to the other:
memcpy( img->imageData,
image.GetData(),
data_size );
Thresholding the grayscale image into binary (black & white)
The OpenCV grayscale image is then thresholded to produce a black and white (binary) image, from which we can use for things like detecting the number and location of the spots. Depending on the equipment used and lighting arrangement, some experimentation is probably needed to come up with an optimal threshold value.
cvThreshold( img, // source_img,
img_bw, // destination image
140, // threhold val.
255, // max. val
CV_THRESH_BINARY ); // binary type );
Original FlyCapture grayscale image, set to a Format 7 partial image (24 x 480 pixels) and converted to OpenCV format:
Thresholded to a black and white (binary) image:
Full code listing:
// CameraTest.cpp : Defines entry point for console application.
#include "stdafx.h"
#include "FlyCapture2.h"
#include <cv.h>
#include <highgui.h>
// Disable C4996 warnings
#pragma warning(disable: 4996)
#define SOFTWARE_TRIGGER_CAMERA
using namespace FlyCapture2;
const int col_size = 24;
const int row_size = 480;
const int data_size = row_size * col_size;
// Forward declarations
bool CheckSoftwareTriggerPresence( Camera* pCam );
bool PollForTriggerReady( Camera* pCam );
bool FireSoftwareTrigger( Camera* pCam );
void PrintError( Error error );
void ReleaseImage( IplImage* pimg,
IplImage* pimg_bw,
CvMemStorage* pstorage );
void GrabImages( Camera* pcam,
IplImage* pimg,
IplImage* pimg_bw,
CvMemStorage* pstorage,
int cnt );
// Main Control Loop
int _tmain(int argc, _TCHAR* argv[])
{
Camera cam;
CameraInfo camInfo;
Error error;
BusManager busMgr;
PGRGuid guid;
Format7PacketInfo fmt7PacketInfo;
Format7ImageSettings fmt7ImageSettings;
CvMemStorage* storage = NULL;
IplImage* img = NULL;
IplImage* img_bw = NULL;
TriggerMode triggerMode;
// Create OpenCV structs for grayscale image
img = cvCreateImage( cvSize( col_size, row_size ),
IPL_DEPTH_8U,
1 );
img_bw = cvCloneImage( img );
storage = cvCreateMemStorage( 0 );
// Get Flea2 camera
error = busMgr.GetCameraFromIndex( 0, &guid );
if ( error != PGRERROR_OK )
{
PrintError( error );
return -1;
}
// Connect to the camera
error = cam.Connect( &guid );
if ( error != PGRERROR_OK )
{
PrintError( error );
return -1;
}
// Get camera information
error = cam.GetCameraInfo(&camInfo);
if ( error != PGRERROR_OK )
{
PrintError( error );
return -1;
}
#ifndef SOFTWARE_TRIGGER_CAMERA
// Check for external trigger support
TriggerModeInfo triggerModeInfo;
error = cam.GetTriggerModeInfo( &triggerModeInfo ;
if ( error != PGRERROR_OK )
{
PrintError( error );
return -1;
}
if ( triggerModeInfo.present != true )
{
printf( "Camera doesn't support external trigger!\n" );
return -1;
}
#endif
// Get current trigger settings
error = cam.GetTriggerMode( &triggerMode );
if ( error != PGRERROR_OK )
{
PrintError( error );
return -1;
}
// Set camera to trigger mode 0
triggerMode.onOff = true;
triggerMode.mode = 0;
triggerMode.parameter = 0;
#ifdef SOFTWARE_TRIGGER_CAMERA
// A source of 7 means software trigger
triggerMode.source = 7;
#else
// Triggering the camera externally using source 0.
triggerMode.source = 0;
#endif
// Set camera triggering mode
error = cam.SetTriggerMode( &triggerMode );
if ( error != PGRERROR_OK )
{
PrintError( error );
return -1;
}
// Power on the camera
const unsigned int k_cameraPower = 0x610;
const unsigned int k_powerVal = 0x80000000;
error = cam.WriteRegister( k_cameraPower, k_powerVal );
if ( error != PGRERROR_OK )
{
PrintError( error );
return -1;
}
// Poll to ensure camera is ready
bool retVal = PollForTriggerReady( &cam );
if( !retVal )
{
PrintError( error );
return -1;
}
// Set camera configuration: region of 24 x 480 pixels
// greyscale image mode
fmt7ImageSettings.width = col_size;
fmt7ImageSettings.height = row_size;
fmt7ImageSettings.mode = MODE_0;
fmt7ImageSettings.offsetX = 312;
fmt7ImageSettings.offsetY = 0;
fmt7ImageSettings.pixelFormat = PIXEL_FORMAT_MONO8;
// Validate Format 7 settings
bool valid;
error = cam.ValidateFormat7Settings( &fmt7ImageSettings,
&valid,
&fmt7PacketInfo );
unsigned int num_bytes =
fmt7PacketInfo.recommendedBytesPerPacket;
// Set Format 7 (partial image mode) settings
error = cam.SetFormat7Configuration( &fmt7ImageSettings,
num_bytes );
if ( error != PGRERROR_OK)
{
PrintError( error );
return -1;
}
// Start capturing images
error = cam.StartCapture();
if ( error != PGRERROR_OK )
{
PrintError( error );
return -1;
}
#ifdef SOFTWARE_TRIGGER_CAMERA
if ( !CheckSoftwareTriggerPresence( &cam ) )
{
printf( "SOFT_ASYNC_TRIGGER not implemented on "
"this camera! Stopping application\n" );
return -1;
}
#else
printf( "Trigger the camera by sending a trigger pulse"
" to GPIO%d.\n",
triggerMode.source );
#endif
error = cam.StartCapture();
// Warm up - necessary to get decent images.
// See Flea2 Technical Ref.: camera will typically not
// send first 2 images acquired after power-up
// It may therefore take several (n) images to get
// satisfactory image, where n is undefined
for ( int i = 0; i < 30; i++ )
{
// Check that the trigger is ready
PollForTriggerReady( &cam );
// Fire software trigger
FireSoftwareTrigger( &cam );
Image im;
// Retrieve image before starting main loop
Error error = cam.RetrieveBuffer( &im );
if ( error != PGRERROR_OK )
{
PrintError( error );
return -1;
}
}
#ifdef SOFTWARE_TRIGGER_CAMERA
if ( !CheckSoftwareTriggerPresence( &cam ) )
{
printf( "SOFT_ASYNC_TRIGGER not implemented on this"
" camera! Stopping application\n");
return -1;
}
#else
printf( "Trigger camera by sending trigger pulse to"
" GPIO%d.\n",
triggerMode.source );
#endif
// Grab images acc. to number of hw/sw trigger events
for ( int i = 0; i < 25; i++ )
{
GrabImages( &cam, img, img_bw, storage, i );
}
// Turn trigger mode off.
triggerMode.onOff = false;
error = cam.SetTriggerMode( &triggerMode );
if ( error != PGRERROR_OK )
{
PrintError( error );
return -1;
}
printf( "\nFinished grabbing images\n" );
// Stop capturing images error = cam.StopCapture();
if ( error != PGRERROR_OK )
{
PrintError( error );
return -1;
}
// Disconnect the camera
error = cam.Disconnect();
if ( error != PGRERROR_OK )
{
PrintError( error );
return -1;
}
ReleaseImage( img, img_bw, storage);
return 0;
}
// Print error trace
void PrintError( Error error )
{
error.PrintErrorTrace();
}
// Check for the presence of software trigger
bool CheckSoftwareTriggerPresence( Camera* pCam )
{
const unsigned int k_triggerInq = 0x530;
Error error;
unsigned int regVal = 0;
error = pCam->ReadRegister( k_triggerInq, ®Val );
if ( error != PGRERROR_OK )
{
// TODO
}
if( ( regVal & 0x10000 ) != 0x10000 )
{
return false;
}
return true;
}
// Start polling for trigger ready
bool PollForTriggerReady( Camera* pCam )
{
const unsigned int k_softwareTrigger = 0x62C;
Error error;
unsigned int regVal = 0;
do
{
error = pCam->ReadRegister( k_softwareTrigger,
regVal );
if ( error != PGRERROR_OK )
{
// TODO
}
} while ( (regVal >> 31) != 0 );
return true;
}
// Launch the software trigger event
bool FireSoftwareTrigger( Camera* pCam )
{
const unsigned int k_softwareTrigger = 0x62C;
const unsigned int k_fireVal = 0x80000000;
Error error;
error = pCam->WriteRegister( k_softwareTrigger,
k_fireVal );
if ( error != PGRERROR_OK )
{
// TODO
}
return true;
}
// Tidy up memory allocated for images etc
void ReleaseImage( IplImage* pimg,
IplImage* pimg_bw,
CvMemStorage* pstorage )
{
cvReleaseImage( &pimg );
cvReleaseImage( &pimg_bw );
cvClearMemStorage( pstorage );
}
// Grab camera grayscale image and convert into
// an OpenCV image
void GrabImages( Camera* pcam,
IplImage* pimg,
IplImage* pimg_bw,
CvMemStorage* pstorage,
int cnt )
{
Image image;
#ifdef SOFTWARE_TRIGGER_CAMERA
// Check that the trigger is ready
PollForTriggerReady( pcam );
printf( "Press Enter to initiate software trigger.\n" );
getchar();
// Fire software trigger
bool retVal = FireSoftwareTrigger( pcam );
if ( !retVal )
{
// TODO.
}
#endif
// Retrieve image before starting main loop
Error error = pcam->RetrieveBuffer( &image );
if ( error != PGRERROR_OK )
{
// TODO.
}
// Copy FlyCapture2 image into OpenCV struct
memcpy( pimg->imageData,
image.GetData(),
data_size );
// Save the bitmap to file
cvSaveImage( "orig.bmp", pimg );
// Threshold to convert image into binary (B&W)
cvThreshold( pimg, // source image
pimg_bw, // destination image
145, // threhold val.
255, // max. val
CV_THRESH_BINARY ); // binary type );
// Save the bitmap to file
char buffer[ 20 ];
sprintf( buffer, "%d", cnt );
std::string mess = "B_W.bmp_";
mess.append( buffer );
mess.append( ".bmp" );
cvSaveImage( mess.c_str(), pimg_bw );
// Find connected components using OpenCV
// for black spots against a white background
CvSeq* seq;
int num_blobs = cvFindContours( pimg_bw,
pstorage,
&seq,
sizeof( CvContour ),
CV_RETR_LIST,
CV_CHAIN_APPROX_NONE,
cvPoint( 0, 0 ) ) - 1;
}
Other posts related to image detection
Tracking Coloured Objects in Video using OpenCV
Displaying AVI Video using OpenCV
Analyzing FlyCapture2 Images obtained from Flea2 Cameras
OpenCV Detection of Dark Objects Against Light Backgrounds
Getting Started with OpenCV in Visual Studio
Object Detection Using the OpenCV / cvBlobsLib Libraries
