opencv background substraction - opencv

I have an image of the background scene and an image of the same scene with objects in front. Now I want to create a mask of the object in the foreground with background substraction. Both images are RGB.
I have already created the following code:
cv::Mat diff;
diff.create(orgImage.dims, orgImage.size, CV_8UC3);
diff = abs(orgImage-refImage);
cv::Mat mask(diff.rows, diff.cols, CV_8U, cv::Scalar(0,0,0));
//mask = (diff > 10);
for (int j=0; j<diff.rows; j++) {
// get the address of row j
//uchar* dataIn= diff.ptr<uchar>(j);
//uchar* dataOut= mask.ptr<uchar>(j);
for (int i=0; i<diff.cols; i++) {
if(diff.at<cv::Vec3b>(j,i)[0] > 30 || diff.at<cv::Vec3b>(j,i)[1] > 30 || diff.at<cv::Vec3b>(j,i)[2] > 30)
mask.at<uchar>(j,i) = 255;
}
}
I dont know if I am doing this right?

Have a look at the inRange function from OpenCV. This will allow you to set multiple thresholds at the same time for a 3 channel image.
So, to create the mask you were looking for, do the following:
inRange(diff, Scalar(30, 30, 30), Scalar(255, 255, 255), mask);
This should also be faster than trying to access each pixel yourself.
EDIT : If skin detection is what you are trying to do, I would first do skin detection, and then afterwards do background subtraction to remove the background. Otherwise, your skin detector will have to take into account the intensity shift caused by the subtraction.
Check out my other answer, about good techniques for skin detection.
EDIT :
Is this any faster?
int main(int argc, char* argv[])
{
Mat fg = imread("fg.jpg");
Mat bg = imread("bg.jpg");
cvtColor(fg, fg, CV_RGB2YCrCb);
cvtColor(bg, bg, CV_RGB2YCrCb);
Mat distance = Mat::zeros(fg.size(), CV_32F);
vector<Mat> fgChannels;
split(fg, fgChannels);
vector<Mat> bgChannels;
split(bg, bgChannels);
for(size_t i = 0; i < fgChannels.size(); i++)
{
Mat temp = abs(fgChannels[i] - bgChannels[i]);
temp.convertTo(temp, CV_32F);
distance = distance + temp;
}
Mat mask;
threshold(distance, mask, 35, 255, THRESH_BINARY);
Mat kernel5x5 = getStructuringElement(MORPH_RECT, Size(5, 5));
morphologyEx(mask, mask, MORPH_OPEN, kernel5x5);
imshow("fg", fg);
imshow("bg", bg);
imshow("mask", mask);
waitKey();
return 0;
}
This code produces this mask based on your input imagery:
Finally, here is what I get using my simple thresholding method:
Mat diff = fgYcc - bgYcc;
vector<Mat> diffChannels;
split(diff, diffChannels);
// only operating on luminance for background subtraction...
threshold(diffChannels[0], bgfgMask, 1, 255.0, THRESH_BINARY_INV);
Mat kernel5x5 = getStructuringElement(MORPH_RECT, Size(5, 5));
morphologyEx(bgfgMask, bgfgMask, MORPH_OPEN, kernel5x5);
This produce the following mask:

I think when I'm doing it like this I get the right results: (in the YCrCb colorspace) but accessing each px is slow so I need to find another algorithm
cv::Mat mask(image.rows, image.cols, CV_8U, cv::Scalar(0,0,0));
cv::Mat_<cv::Vec3b>::const_iterator itImage= image.begin<cv::Vec3b>();
cv::Mat_<cv::Vec3b>::const_iterator itend= image.end<cv::Vec3b>();
cv::Mat_<cv::Vec3b>::iterator itRef= refRoi.begin<cv::Vec3b>();
cv::Mat_<uchar>::iterator itMask= mask.begin<uchar>();
for ( ; itImage!= itend; ++itImage, ++itRef, ++itMask) {
int distance = abs((*itImage)[0]-(*itRef)[0])+
abs((*itImage)[1]-(*itRef)[1])+
abs((*itImage)[2]-(*itRef)[2]);
if(distance < 30)
*itMask = 0;
else
*itMask = 255;
}

Related

object detection of various shapes in opencv

I have an image and want to detect various objects at a time using opencv methods.
I have tried detecting one object using contouring and using the area to filter other counters. But I need to detect other objects too but they vary in area and length.
Can anyone help me to use any methods for detecting it.
This is the original image:
this is the code that I have tried for detection:
int main()
{
Mat msrc = imread("Task6_Resources/Scratch.jpg", 1);
Mat src = imread("Task6_Resources/Scratch.jpg", 0);
Mat imgblur;
GaussianBlur(src, imgblur, Size(13,13), 0);
cv::Ptr<cv::CLAHE> clahe = cv::createCLAHE();
clahe->setClipLimit(8);
cv::Mat gcimg;
clahe->apply(imgblur, gcimg);
Mat thresh;
threshold(gcimg, thresh, 55, 255, THRESH_BINARY_INV);
Mat th_mina = minareafilter(thresh, 195); //function used to filter small and large blobs
Mat th_maxa = maxareafilter(th_mina, 393);
Mat imdilate;
dilate(th_maxa, imdilate, getStructuringElement(MORPH_RECT, Size(3, 1)), Point(-1, -1), 7);
int largest_area = 0;
int largest_contour_index = 0;
Rect bounding_rect;
vector<vector<Point>> contours;
vector<Vec4i> hierarchy;
findContours(imdilate, contours, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE);
cout << "Number of contours" << contours.size() << endl;
//Largest contour according to area
for (int i = 0; i < contours.size(); i++){
double a = contourArea(contours[i], false);
if (a > largest_area) {
largest_area = a;
largest_contour_index = i;
bounding_rect = boundingRect(contours[i]);
}
}
for (int c = 0; c < contours.size(); c++){
printf(" * Contour[%d] Area OpenCV: %.2f - Length: %.2f \n",
c,contourArea(contours[c]), arcLength(contours[c], true));
}
rectangle(msrc, bounding_rect, Scalar(0, 255, 0), 2, 8, 0);
imshow("largest contour", msrc);
waitKey(0);
destroyAllWindows();
return 0;
}
This is the image on which I am applying contouring
After the code I am able to detect the green box using largest area in contouring, but I need to detect those red boxes too. (only the region of red boxes)
The problem is here I cannot apply again area parameter to filter the contours as some other contours have same area as the resultant contour.
The image result required:

OpenCV: Retrieving color of the center of a contour

Im trying to detect the colour of a set of shapes in a black image using OpenCV, for which I use Canny detection. However the color output always comes back as black.
std::vector<std::pair<cv::Point, cv::Vec3b> > Asteroids::DetectPoints(const cv::Mat &image)
{
cv::Mat imageGray;
cv::cvtColor( image, imageGray, CV_BGR2GRAY );
cv::threshold(imageGray, imageGray, 1, 255, cv::THRESH_BINARY);
cv::Mat canny_output;
std::vector<std::vector<cv::Point> > contours;
std::vector<cv::Vec4i> hierarchy;
int thresh = 10;
// Detect edges using canny
cv::Canny( imageGray, canny_output, thresh, thresh*2, 3 );
// Find contours
cv::findContours( canny_output, contours, hierarchy, CV_RETR_LIST, CV_CHAIN_APPROX_NONE, cv::Point(0, 0) );
std::vector<std::pair<cv::Point, cv::Vec3b> > points;
for(unsigned int i = 0; i < contours.size(); i++ )
{
cv::Rect rect = cv::boundingRect(contours[i]);
std::pair<cv::Point, cv::Vec3b> posColor;
posColor.first = cv::Point( rect.tl().x + (rect.size().width / 2), rect.tl().y + (rect.size().height / 2));
posColor.second = image.at<cv::Vec3b>( posColor.first.x, posColor.first.y );
//Dont add teh entry to the list if one with the same color and position is already pressent,
//The contour detection sometimes returns duplicates
bool isInList = false;
for(unsigned int j = 0; j < points.size(); j++)
if(points[j].first == posColor.first && points[j].second == posColor.second)
isInList = true;
if(!isInList)
points.push_back( posColor );
}
return points;
}
I know it has to be an issue with the positions or something along those lines, but I cant figure out what
I might be wrong, but off the top of my head :
Shouldn't this read
posColor.second = image.at<cv::Vec3b>(posColor.first.y, posColor.first.x);
and not the other way around like you did it ?
Matrix notation, not cartesian notation ?

Image Sharpening Using Laplacian Filter

I was trying to sharpening on some standard image from Gonzalez books. Below are some code that I have tried but it doesn't get closer to the results of the sharpened image.
cvSmooth(grayImg, grayImg, CV_GAUSSIAN, 3, 0, 0, 0);
IplImage* laplaceImg = cvCreateImage(cvGetSize(oriImg), IPL_DEPTH_16S, 1);
IplImage* abs_laplaceImg = cvCreateImage(cvGetSize(oriImg), IPL_DEPTH_8U, 1);
cvLaplace(grayImg, laplaceImg, 3);
cvConvertScaleAbs(laplaceImg, abs_laplaceImg, 1, 0);
IplImage* dstImg = cvCreateImage(cvGetSize(oriImg), IPL_DEPTH_8U, 1);
cvAdd(abs_laplaceImg, grayImg, dstImg, NULL);
Before Sharpening
My Sharpening Result
Desired Result
Absolute Laplace
I think the problem is that you are blurring the image before take the 2nd derivate.
Here is the working code with the C++ API (I'm using Opencv 2.4.3). I tried also with MATLAB and the result is the same.
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <iostream>
using namespace cv;
using namespace std;
int main(int /*argc*/, char** /*argv*/) {
Mat img, imgLaplacian, imgResult;
//------------------------------------------------------------------------------------------- test, first of all
// now do it by hand
img = (Mat_<uchar>(4,4) << 0,1,2,3,4,5,6,7,8,9,0,11,12,13,14,15);
// first, the good result
Laplacian(img, imgLaplacian, CV_8UC1);
cout << "let opencv do it" << endl;
cout << imgLaplacian << endl;
Mat kernel = (Mat_<float>(3,3) <<
0, 1, 0,
1, -4, 1,
0, 1, 0);
int window_size = 3;
// now, reaaallly by hand
// note that, for avoiding padding, the result image will be smaller than the original one.
Mat frame, frame32;
Rect roi;
imgLaplacian = Mat::zeros(img.size(), CV_32F);
for(int y=0; y<img.rows-window_size/2-1; y++) {
for(int x=0; x<img.cols-window_size/2-1; x++) {
roi = Rect(x,y, window_size, window_size);
frame = img(roi);
frame.convertTo(frame, CV_32F);
frame = frame.mul(kernel);
float v = sum(frame)[0];
imgLaplacian.at<float>(y,x) = v;
}
}
imgLaplacian.convertTo(imgLaplacian, CV_8U);
cout << "dudee" << imgLaplacian << endl;
// a little bit less "by hand"..
// using cv::filter2D
filter2D(img, imgLaplacian, -1, kernel);
cout << imgLaplacian << endl;
//------------------------------------------------------------------------------------------- real stuffs now
img = imread("moon.jpg", 0); // load grayscale image
// ok, now try different kernel
kernel = (Mat_<float>(3,3) <<
1, 1, 1,
1, -8, 1,
1, 1, 1); // another approximation of second derivate, more stronger
// do the laplacian filtering as it is
// well, we need to convert everything in something more deeper then CV_8U
// because the kernel has some negative values,
// and we can expect in general to have a Laplacian image with negative values
// BUT a 8bits unsigned int (the one we are working with) can contain values from 0 to 255
// so the possible negative number will be truncated
filter2D(img, imgLaplacian, CV_32F, kernel);
img.convertTo(img, CV_32F);
imgResult = img - imgLaplacian;
// convert back to 8bits gray scale
imgResult.convertTo(imgResult, CV_8U);
imgLaplacian.convertTo(imgLaplacian, CV_8U);
namedWindow("laplacian", CV_WINDOW_AUTOSIZE);
imshow( "laplacian", imgLaplacian );
namedWindow("result", CV_WINDOW_AUTOSIZE);
imshow( "result", imgResult );
while( true ) {
char c = (char)waitKey(10);
if( c == 27 ) { break; }
}
return 0;
}
Have fun!
I think the main problem lies in the fact that you do img + laplace, while img - laplace would give better results. I remember that img - 2*laplace was best, but I cannot find where I read that, probably in one of the books I read in university.
You need to do img - laplace instead of img + laplace.
laplace: f(x,y) = f(x-1,y+1) + f(x-1,y-1) + f(x,y+1) + f(x+1,y) - 4*f(x,y)
So, if you see subtract laplace from the original image you would see that the minus sign in front of 4*f(x,y) gets negated and this term becomes positive.
You could also have kernel with -5 in the center pixel instead of -4 to make the laplacian a one-step process instead of getting the getting the laplace and doing img - laplace Why? Try deriving that yourself.
This would be the final kernel.
Mat kernel = (Mat_(3,3) <<
-1, 0, -1,
0, -5, 0,
-1, 0, -1);
It is indeed a well-known result in image processing that if you subtract its Laplacian from an image, the image edges are amplified giving a sharper image.
Laplacian Filter Kernel algorithm: sharpened_pixel = 5 * current – left – right – up – down
enter image description here
So the Code will look like these:
void sharpen(const Mat& img, Mat& result)
{
result.create(img.size(), img.type());
//Processing the inner edge of the pixel point, the image of the outer edge of the pixel should be additional processing
for (int row = 1; row < img.rows-1; row++)
{
//Front row pixel
const uchar* previous = img.ptr<const uchar>(row-1);
//Current line to be processed
const uchar* current = img.ptr<const uchar>(row);
//new row
const uchar* next = img.ptr<const uchar>(row+1);
uchar *output = result.ptr<uchar>(row);
int ch = img.channels();
int starts = ch;
int ends = (img.cols - 1) * ch;
for (int col = starts; col < ends; col++)
{
//The traversing pointer of the output image is synchronized with the current row, and each channel value of each pixel in each row is given a increment, because the channel number of the image is to be taken into account.
*output++ = saturate_cast<uchar>(5 * current[col] - current[col-ch] - current[col+ch] - previous[col] - next[col]);
}
} //end loop
//Processing boundary, the peripheral pixel is set to 0
result.row(0).setTo(Scalar::all(0));
result.row(result.rows-1).setTo(Scalar::all(0));
result.col(0).setTo(Scalar::all(0));
result.col(result.cols-1).setTo(Scalar::all(0));
}
int main()
{
Mat lena = imread("lena.jpg");
Mat sharpenedLena;
ggicci::sharpen(lena, sharpenedLena);
imshow("lena", lena);
imshow("sharpened lena", sharpenedLena);
cvWaitKey();
return 0;
}
If you are a lazier. Have fun with the following.
int main()
{
Mat lena = imread("lena.jpg");
Mat sharpenedLena;
Mat kernel = (Mat_<float>(3, 3) << 0, -1, 0, -1, 4, -1, 0, -1, 0);
cv::filter2D(lena, sharpenedLena, lena.depth(), kernel);
imshow("lena", lena);
imshow("sharpened lena", sharpenedLena);
cvWaitKey();
return 0;
}
And the result like these.enter image description here

Read HSV value of pixel in opencv

how would you go about reading the pixel value in HSV format rather than RGB? The code below reads the pixel value of the circles' centers in RGB format. Is there much difference when it comes to reading value in HSV?
int main(int argc, char** argv)
{
//load image from directory
IplImage* img = cvLoadImage("C:\\Users\\Nathan\\Desktop\\SnookerPic.png");
IplImage* gray = cvCreateImage(cvGetSize(img), IPL_DEPTH_8U, 1);
CvMemStorage* storage = cvCreateMemStorage(0);
//covert to grayscale
cvCvtColor(img, gray, CV_BGR2GRAY);
// This is done so as to prevent a lot of false circles from being detected
cvSmooth(gray, gray, CV_GAUSSIAN, 7, 7);
IplImage* canny = cvCreateImage(cvGetSize(img),IPL_DEPTH_8U,1);
IplImage* rgbcanny = cvCreateImage(cvGetSize(img),IPL_DEPTH_8U,3);
cvCanny(gray, canny, 50, 100, 3);
//detect circles
CvSeq* circles = cvHoughCircles(gray, storage, CV_HOUGH_GRADIENT, 1, 35.0, 75, 60,0,0);
cvCvtColor(canny, rgbcanny, CV_GRAY2BGR);
//draw all detected circles
for (int i = 0; i < circles->total; i++)
{
// round the floats to an int
float* p = (float*)cvGetSeqElem(circles, i);
cv::Point center(cvRound(p[0]), cvRound(p[1]));
int radius = cvRound(p[2]);
//uchar* ptr;
//ptr = cvPtr2D(img, center.y, center.x, NULL);
//printf("B: %d G: %d R: %d\n", ptr[0],ptr[1],ptr[2]);
CvScalar s;
s = cvGet2D(img,center.y, center.x);//colour of circle
printf("B: %f G: %f R: %f\n",s.val[0],s.val[1],s.val[2]);
// draw the circle center
cvCircle(img, center, 3, CV_RGB(0,255,0), -1, 8, 0 );
// draw the circle outline
cvCircle(img, center, radius+1, CV_RGB(0,0,255), 2, 8, 0 );
//display coordinates
printf("x: %d y: %d r: %d\n",center.x,center.y, radius);
}
//create window
//cvNamedWindow("circles", 1);
cvNamedWindow("SnookerImage", 1);
//show image in window
//cvShowImage("circles", rgbcanny);
cvShowImage("SnookerImage", img);
cvSaveImage("out.png", img);
//cvDestroyWindow("SnookerImage");
//cvDestroyWindow("circles");
//cvReleaseMemStorage("storage");
cvWaitKey(0);
return 0;
}
If you use the C++ interface, you can use
cv::cvtColor(img, img, CV_BGR2HSV);
See the documentation for cvtColor for more information.
Update:
Reading and writing pixels the slow way (assuming that the HSV values are stored as a cv::Vec3b (doc))
cv::Vec3b pixel = image.at<cv::Vec3b>(0,0); // read pixel (0,0) (make copy)
pixel[0] = 0; // H
pixel[1] = 0; // S
pixel[2] = 0; // V
image.at<cv::Vec3b>(0,0) = pixel; // write pixel (0,0) (copy pixel back to image)
Using the image.at<...>(x, y) (doc, scroll down a lot) notation is quite slow, if you want to manipulate every pixel. There is an article in the documentation on how to access the pixels faster. You can apply the iterator method also like this:
cv::MatIterator_<cv::Vec3b> it = image.begin<cv::Vec3b>(),
it_end = image.end<cv::Vec3b>();
for(; it != it_end; ++it)
{
// work with pixel in here, e.g.:
cv::Vec3b& pixel = *it; // reference to pixel in image
pixel[0] = 0; // changes pixel in image
}

Getting black and white intensity values from a histogram

I am trying to get black and white histogram data from a color image. However the current setup I have with my histogram only shows me color data I'm sure that it's something that I have to modify in my current math setup.
// Current setup on how to render histogram data to the screen with hist being the calculated histogram
histimg = Mat::zeros(200, 320, CV_8UC3)
int binW = histimg.cols / 16;
Mat buf(1, 16, CV_8UC3);
for( int i = 0; i < 16; i++ )
{
buf.at<Vec3b>(i) = Vec3b(saturate_cast<uchar>(i*180./16), 255, 255);
}
cvtColor(buf, buf, CV_HSV2BGR);
for( int i = 0; i < 16; i++ )
{
int val = saturate_cast<int>(hist.at<float>(i)*histimg.rows/255);
rectangle( histimg, Point(i*binW,histimg.rows),
Point((i+1)*binW,histimg.rows - val),
Scalar(buf.at<Vec3b>(i)), -1, 8 );
}
Thanks in advance for any advice.
Here are two methods:
Create whiteCount and blackCount variables. Iterate through all the pixels and increment whiteCount if the pixel is (255, 255, 255) and increment blackCount if the pixel is (0, 0, 0).
Convert the image to grayscale, create a histogram and look at the first and last bins.

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