Split image frame into 8*8 for DCT using OpenCV and C++ - c++

Question

I need to pass fullPath into method FrameTo8by8(). In FrameTo8by8(), it will split the every frame into 8*8 blocks. (E.g. My video resolution is 1280*720 = 921,600. After that 921,600 / 64(8*8) = 14,400. So there will be total of 14,400 blocks of 8*8).
VideoSplitEngine.h
class VideoSplitEngine
{
public:
static VideoCapture capture;
static Mat fullimage;
//Default constructor
VideoSplitEngine();
//Declare a virtual destructor:
virtual ~VideoSplitEngine();
//Method
Mat Start();
void FrameTo8by8() const;
string GetFilePath() const;
private:
};
VideoSplitEngine.cpp
#include "StdAfx.h"
#include "VideoSplitEngine.h"
#include "UserInfo.h"
#include "Common.h"
VideoCapture VideoSplitEngine::capture;
Mat VideoSplitEngine::fullimage;
Mat VideoSplitEngine::Start()
string VideoSplitEngine::GetFilePath() const
{
cout<< endl;
cout << "Place video in Desktop and enter file name (e.g. vid.avi):" << endl;
cout<<"----------------------------------------------------------"<< endl;
//Get user desktop file path
string fullPath;
string userProfile = getenv("userprofile"); //GetEnvironmentVariable() is to get current userprofile (e.g."C:\Users\L30807")
string path = userProfile + "\\Desktop\\";
string vid;
getline (cin, vid); //Prompt to input file name
fullPath = path + vid;
capture.open(fullPath); //Read video
cout<< endl;
return fullPath;
}
Mat VideoSplitEngine::Start()
{
while(1)
{
bool bSuccess = capture.read(fullimage); // read a new frame from video
if (!bSuccess) //if not success, break loop
{
cout << "End of video" << endl;
destroyWindow("Original Video");
break;
}
imshow("Original Video", fullimage); //show the frame in "Original Video" window
if(waitKey(30) == 27) //wait for 'esc' key press for 30 ms. If 'esc' key is pressed, break loop
{
cout << "esc key is pressed by user" << endl;
break;
}
}
return fullimage;
}
void VideoSplitEngine::FrameTo8by8() const
{
namedWindow("Original", CV_WINDOW_AUTOSIZE);
imshow("Original", fullimage);
int width = fullimage.size().width;
int height = fullimage.size().width;
cout << "Original image Width x Height is " << width << "x" << height << endl;
// Leave original alone, work on a copy
Mat dctImage = fullimage.clone();
// Step through the copied image with rectangles size 8x8
// For each block, split into planes, do dct, and merge back
// into the block. (This will affect the image from
// which the block is selected each time.)
for (int i = 0; i < height; i += 8)
{
for (int j = 0; j < width; j+= 8)
{
Mat block = dctImage(Rect(i, j, 8, 8));
vector<Mat> planes;
split(block, planes);
vector<Mat> outplanes(planes.size());
for (size_t k = 0; k < planes.size(); k++)
{
planes[k].convertTo(planes[k], CV_32FC1);
dct(planes[k], outplanes[k]);
outplanes[k].convertTo(outplanes[k], CV_8UC1);
}
merge(outplanes, block);
}
}
namedWindow("dctBlockImage");
imshow("dctBlockImage", dctImage);
waitKey(30);
}
I need help on how to split it or is there other methods to do it?

Answer 1

1.#berak is right.The prototype of function Rect() is Rect(x,y,width,height).So 'j' which refer to 'width' should be 'x'.(Actually I havn't found the prototype of Rect() from http://docs.opencv.org/2.4/index.html ,but cvRect() in the C API is cvRect(x,y,width,height).I think their prototypes maybe the same.)
2.for (int i = 0; i < height; i += 8) and for (int j = 0; j < width; j+= 8) will cause the error ""Unhandled exception at ...".By changing them to for (int i = 0; i < (height/8)*8; i += 8)andfor (int j = 0; j < (width/8)*8; j+= 8),this error will be sovled.
3.#user3743939 If you managed to sovle your problem,please post your solution to help others.
regards