Reads an image from a buffer in memory.
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The function reads image from the specified buffer in memory. If the buffer is too short or contains invalid data, the empty matrix will be returned.
See imread for the list of supported formats and the flags description.
Encode an image into a memory buffer.
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The function compresses the image and stores it in the memory buffer, which is resized to fit the result. See imwrite for the list of supported formats and the flags description.
Loads an image from a file.
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The function imread loads an image from the specified file and returns it. If the image can not be read (because of missing file, improper permissions, unsupported or invalid format), the function returns empty matrix ( Mat::data==NULL ).Currently, the following file formats are supported:
Note1 : The function determines type of the image by the content, not by the file extension.
Note2 : On Windows and MacOSX the shipped with OpenCV image codecs (libjpeg, libpng, libtiff and libjasper) are used by default; so OpenCV can always read JPEGs, PNGs and TIFFs. On MacOSX there is also the option to use native MacOSX image readers. But beware that currently these native image loaders give images with somewhat different pixel values, because of the embedded into MacOSX color management.
On Linux, BSD flavors and other Unix-like open-source operating systems OpenCV looks for the supplied with OS image codecs. Please, install the relevant packages (do not forget the development files, e.g. “libjpeg-dev” etc. in Debian and Ubuntu) in order to get the codec support, or turn on OPENCV_BUILD_3RDPARTY_LIBS flag in CMake.
Saves an image to a specified file.
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The function imwrite saves the image to the specified file. The image format is chosen based on the filename extension, see imread for the list of extensions. Only 8-bit (or 16-bit in the case of PNG, JPEG 2000 and TIFF) single-channel or 3-channel (with ‘BGR’ channel order) images can be saved using this function. If the format, depth or channel order is different, use Mat::convertTo , and cvtColor to convert it before saving, or use the universal XML I/O functions to save the image to XML or YAML format.
Class for video capturing from video files or cameras
class VideoCapture
{
public:
// the default constructor
VideoCapture();
// the constructor that opens video file
VideoCapture(const string& filename);
// the constructor that starts streaming from the camera
VideoCapture(int device);
// the destructor
virtual ~VideoCapture();
// opens the specified video file
virtual bool open(const string& filename);
// starts streaming from the specified camera by its id
virtual bool open(int device);
// returns true if the file was open successfully or if the camera
// has been initialized succesfully
virtual bool isOpened() const;
// closes the camera stream or the video file
// (automatically called by the destructor)
virtual void release();
// grab the next frame or a set of frames from a multi-head camera;
// returns false if there are no more frames
virtual bool grab();
// reads the frame from the specified video stream
// (non-zero channel is only valid for multi-head camera live streams)
virtual bool retrieve(Mat& image, int channel=0);
// equivalent to grab() + retrieve(image, 0);
virtual VideoCapture& operator >> (Mat& image);
// sets the specified property propId to the specified value
virtual bool set(int propId, double value);
// retrieves value of the specified property
virtual double get(int propId);
protected:
...
};
The class provides C++ video capturing API. Here is how the class can be used:
#include "cv.h"
#include "highgui.h"
using namespace cv;
int main(int, char**)
{
VideoCapture cap(0); // open the default camera
if(!cap.isOpened()) // check if we succeeded
return -1;
Mat edges;
namedWindow("edges",1);
for(;;)
{
Mat frame;
cap >> frame; // get a new frame from camera
cvtColor(frame, edges, CV_BGR2GRAY);
GaussianBlur(edges, edges, Size(7,7), 1.5, 1.5);
Canny(edges, edges, 0, 30, 3);
imshow("edges", edges);
if(waitKey(30) >= 0) break;
}
// the camera will be deinitialized automatically in VideoCapture destructor
return 0;
}
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VideoCapture constructors.
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Note that when querying a property which is unsupported by the backend used by the VideoCapture class, the value 0 is returned.
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Sets a property in the VideoCapture backend.
Video writer class
class VideoWriter
{
public:
// default constructor
VideoWriter();
// constructor that calls open
VideoWriter(const string& filename, int fourcc,
double fps, Size frameSize, bool isColor=true);
// the destructor
virtual ~VideoWriter();
// opens the file and initializes the video writer.
// filename - the output file name.
// fourcc - the codec
// fps - the number of frames per second
// frameSize - the video frame size
// isColor - specifies whether the video stream is color or grayscale
virtual bool open(const string& filename, int fourcc,
double fps, Size frameSize, bool isColor=true);
// returns true if the writer has been initialized successfully
virtual bool isOpened() const;
// writes the next video frame to the stream
virtual VideoWriter& operator << (const Mat& image);
protected:
...
};