I have a Kernel filter that I generated and I want to apply it to my image but I could not get a right result by doing this:
Actually I can use a different method as well since I am not to familiar with opencv I need help thanks.
channel[c] is the read image;
int size = 5; // Gaussian filter box side size
double gauss[5][5];
int sidestp = (size - 1) / 2;
// I have a function to generate the gaussiankernel filter
float sum = 0;
for (int x = 1; x < channels[c].cols - 1; x++){
for (int y = 1; y < channels[c].rows - 1; y++){
for (int i = -size; i <= size; i++){
for (int j = -sidestp; j <= sidestp; j++){
sum = sum + gauss[i + sidestp][j + sidestp] * channels[c].at<uchar>(x - i, y - j);
}
}
result.at<uchar>(y, x) = sum;
}
}
OpenCV has an inbuilt function filter2D that does this convolution for you.
You need to provide your source and destination images, along with the custom kernel (as a Mat), and a few more arguments. See this if it still bothers you.
Just to add to the previous answer, since you are performing Gaussian blur, you can use the OpenCV GaussianBlur (Check here). Unlike filter2D, you can use the standard deviations as input parameter.
Related
I want to create a 1D plot from an image. Then I want to determine the maxima and their distances to each other in c++.
I am looking for some tips on how I could approach this.
I load the image as cv::Mat. In opencv I have searched, but only found the histogram function, which is wrong. I want to get a cross section of the image - from left to right.
does anyone have an idea ?
Well I have the following picture:
From this I want to create a 1D plot like in the following picture (I created the plot in ImageJ).
Here you can see the maxima (I could refine it with "smooth").
I want to determine the positions of these maxima and then the distances between them.
I have to get to the 1D plot somehow. I suppose I can get to the maxima with a derivation?
++++++++++ UPDATE ++++++++++
Now i wrote this to get an 1D Plot:
cv::Mat img= cv::imread(imgFile.toStdString(), cv::IMREAD_ANYDEPTH | cv::IMREAD_COLOR);
cv::cvtColor(img, img, cv::COLOR_BGR2GRAY);
uint8_t* data = img.data;
int width = img.cols;
int height = img.rows;
int stride = img.step;
std::vector<double> vPlot(width, 0);
for (int i = 0; i < height; i++) {
for (int j = 0; j < width; j++) {
uint8_t val = data[ i * stride + j];
vPlot[j]=vPlot[j] + val;
}
}
std::ofstream file;
file.open("path\\plot.csv");
for(int i = 0; i < vPlot.size(); i++){
file << vPlot[i];
file << ";";
}
file.close();
When i plot this in excel i got this:
Thats looks not so smooth as in ImageJ. Did i something wrong?
I need it like in the Plot of ImageJ - more smooth.
ok I got it:
for (int i = 0; i < vPlot.size(); i++) {
vPlot[i] = vPlot[i] / height;
}
Ok but i don't know how to get the maxima an distances.
When i have the local maxima (i don't know how), i can calculate the distance between them with the index of the vetcor elements.
Has anybody an idea to get the local Maxima out of the vector, that I plot above ?
Now o wrote this to find the maxima:
// find maxima
std::vector<int> idxMax;
int flag = 0;
for(int i = 1; i < avg.size(); i++){
double diff = avg[i] - avg[i-1];
if(diff < 0){
if(flag>0){
idxMax.push_back(i);
flag = -1;
}
}
if(diff >= 0){
if(flag<=0){
flag = 1;
}
}
}
But more maxima are found than wanted. The length of the vector varies and also the number of peaks. These can be close together or far away. They are also not always the same height, as can be seen in the picture
I'm currently trying to display an audio spectrum using FFTW3 and SFML. I've followed the directions found here and looked at numerous references on FFT and spectrums and FFTW yet somehow my bars are almost all aligned to the left like below. Another issue I'm having is I can't find information on what the scale of the FFT output is. Currently I'm dividing it by 64 yet it still reaches beyond that occasionally. And further still I have found no information on why the output of the from FFTW has to be the same size as the input. So my questions are:
Why is the majority of my spectrum aligned to the left unlike the image below mine?
Why isn't the output between 0.0 and 1.0?
Why is the input sample count related to the fft output count?
What I get:
What I'm looking for:
const int bufferSize = 256 * 8;
void init() {
sampleCount = (int)buffer.getSampleCount();
channelCount = (int)buffer.getChannelCount();
for (int i = 0; i < bufferSize; i++) {
window.push_back(0.54f - 0.46f * cos(2.0f * GMath::PI * (float)i / (float)bufferSize));
}
plan = fftwf_plan_dft_1d(bufferSize, signal, results, FFTW_FORWARD, FFTW_ESTIMATE);
}
void update() {
int mark = (int)(sound.getPlayingOffset().asSeconds() * sampleRate);
for (int i = 0; i < bufferSize; i++) {
float s = 0.0f;
if (i + mark < sampleCount) {
s = (float)buffer.getSamples()[(i + mark) * channelCount] / (float)SHRT_MAX * window[i];
}
signal[i][0] = s;
signal[i][1] = 0.0f;
}
}
void draw() {
int inc = bufferSize / 2 / size.x;
int y = size.y - 1;
int max = size.y;
for (int i = 0; i < size.x; i ++) {
float total = 0.0f;
for (int j = 0; j < inc; j++) {
int index = i * inc + j;
total += std::sqrt(results[index][0] * results[index][0] + results[index][1] * results[index][1]);
}
total /= (float)(inc * 64);
Rectangle2I rect = Rectangle2I(i, y, 1, -(int)(total * max)).absRect();
g->setPixel(rect, Pixel(254, toColor(BLACK, GREEN)));
}
}
All of your questions are related to the FFT theory. Study the properties of FFT from any standard text/reference book and you will be able to answer your questions all by yourself only.
The least you can start from is here:
https://en.wikipedia.org/wiki/Fast_Fourier_transform.
Many FFT implementations are energy preserving. That means the scale of the output is linearly related to the scale and/or size of the input.
An FFT is a DFT is a square matrix transform. So the number of outputs will always be equal to the number of inputs (or half that by ignoring the redundant complex conjugate half given strictly real input), unless some outputs are thrown away. If not, it's not an FFT. If you want less outputs, there are ways to downsample the FFT output or post process it in other ways.
I wrote a program that loads, saves, and performs the fft and ifft on black and white png images. After much debugging headache, I finally got some coherent output only to find that it distorted the original image.
input:
fft:
ifft:
As far as I have tested, the pixel data in each array is stored and converted correctly. Pixels are stored in two arrays, 'data' which contains the b/w value of each pixel and 'complex_data' which is twice as long as 'data' and stores real b/w value and imaginary parts of each pixel in alternating indices. My fft algorithm operates on an array structured like 'complex_data'. After code to read commands from the user, here's the code in question:
if (cmd == "fft")
{
if (height > width) size = height;
else size = width;
N = (int)pow(2.0, ceil(log((double)size)/log(2.0)));
temp_data = (double*) malloc(sizeof(double) * width * 2); //array to hold each row of the image for processing in FFT()
for (i = 0; i < (int) height; i++)
{
for (j = 0; j < (int) width; j++)
{
temp_data[j*2] = complex_data[(i*width*2)+(j*2)];
temp_data[j*2+1] = complex_data[(i*width*2)+(j*2)+1];
}
FFT(temp_data, N, 1);
for (j = 0; j < (int) width; j++)
{
complex_data[(i*width*2)+(j*2)] = temp_data[j*2];
complex_data[(i*width*2)+(j*2)+1] = temp_data[j*2+1];
}
}
transpose(complex_data, width, height); //tested
free(temp_data);
temp_data = (double*) malloc(sizeof(double) * height * 2);
for (i = 0; i < (int) width; i++)
{
for (j = 0; j < (int) height; j++)
{
temp_data[j*2] = complex_data[(i*height*2)+(j*2)];
temp_data[j*2+1] = complex_data[(i*height*2)+(j*2)+1];
}
FFT(temp_data, N, 1);
for (j = 0; j < (int) height; j++)
{
complex_data[(i*height*2)+(j*2)] = temp_data[j*2];
complex_data[(i*height*2)+(j*2)+1] = temp_data[j*2+1];
}
}
transpose(complex_data, height, width);
free(temp_data);
free(data);
data = complex_to_real(complex_data, image.size()/4); //tested
image = bw_data_to_vector(data, image.size()/4); //tested
cout << "*** fft success ***" << endl << endl;
void FFT(double* data, unsigned long nn, int f_or_b){ // f_or_b is 1 for fft, -1 for ifft
unsigned long n, mmax, m, j, istep, i;
double wtemp, w_real, wp_real, wp_imaginary, w_imaginary, theta;
double temp_real, temp_imaginary;
// reverse-binary reindexing to separate even and odd indices
// and to allow us to compute the FFT in place
n = nn<<1;
j = 1;
for (i = 1; i < n; i += 2) {
if (j > i) {
swap(data[j-1], data[i-1]);
swap(data[j], data[i]);
}
m = nn;
while (m >= 2 && j > m) {
j -= m;
m >>= 1;
}
j += m;
};
// here begins the Danielson-Lanczos section
mmax = 2;
while (n > mmax) {
istep = mmax<<1;
theta = f_or_b * (2 * M_PI/mmax);
wtemp = sin(0.5 * theta);
wp_real = -2.0 * wtemp * wtemp;
wp_imaginary = sin(theta);
w_real = 1.0;
w_imaginary = 0.0;
for (m = 1; m < mmax; m += 2) {
for (i = m; i <= n; i += istep) {
j = i + mmax;
temp_real = w_real * data[j-1] - w_imaginary * data[j];
temp_imaginary = w_real * data[j] + w_imaginary * data[j-1];
data[j-1] = data[i-1] - temp_real;
data[j] = data[i] - temp_imaginary;
data[i-1] += temp_real;
data[i] += temp_imaginary;
}
wtemp = w_real;
w_real += w_real * wp_real - w_imaginary * wp_imaginary;
w_imaginary += w_imaginary * wp_real + wtemp * wp_imaginary;
}
mmax=istep;
}}
My ifft is the same only with the f_or_b set to -1 instead of 1. My program calls FFT() on each row, transposes the image, calls FFT() on each row again, then transposes back. Is there maybe an error with my indexing?
Not an actual answer as this question is Debug only so some hints instead:
your results are really bad
it should look like this:
first line is the actual DFFT result
Re,Im,Power is amplified by a constant otherwise you would see a black image
the last image is IDFFT of the original not amplified Re,IM result
the second line is the same but the DFFT result is wrapped by half size of image in booth x,y to match the common results in most DIP/CV texts
As you can see if you IDFFT back the wrapped results the result is not correct (checker board mask)
You have just single image as DFFT result
is it power spectrum?
or you forget to include imaginary part? to view only or perhaps also to computation somewhere as well?
is your 1D **DFFT working?**
for real data the result should be symmetric
check the links from my comment and compare the results for some sample 1D array
debug/repair your 1D FFT first and only then move to the next level
do not forget to test Real and complex data ...
your IDFFT looks BW (no gray) saturated
so did you amplify the DFFT results to see the image and used that for IDFFT instead of the original DFFT result?
also check if you do not round to integers somewhere along the computation
beware of (I)DFFT overflows/underflows
If your image pixel intensities are big and the resolution of image too then your computation could loss precision. Newer saw this in images but if your image is HDR then it is possible. This is a common problem with convolution computed by DFFT for big polynomials.
Thank you everyone for your opinions. All that stuff about memory corruption, while it makes a point, is not the root of the problem. The sizes of data I'm mallocing are not overly large, and I am freeing them in the right places. I had a lot of practice with this while learning c. The problem was not the fft algorithm either, nor even my 2D implementation of it.
All I missed was the scaling by 1/(M*N) at the very end of my ifft code. Because the image is 512x512, I needed to scale my ifft output by 1/(512*512). Also, my fft looks like white noise because the pixel data was not rescaled to fit between 0 and 255.
Suggest you look at the article http://www.yolinux.com/TUTORIALS/C++MemoryCorruptionAndMemoryLeaks.html
Christophe has a good point but he is wrong about it not being related to the problem because it seems that in modern times using malloc instead of new()/free() does not initialise memory or select best data type which would result in all problems listed below:-
Possibly causes are:
Sign of a number changing somewhere, I have seen similar issues when a platform invoke has been used on a dll and a value is passed by value instead of reference. It is caused by memory not necessarily being empty so when your image data enters it will have boolean maths performed on its values. I would suggest that you make sure memory is empty before you put your image data there.
Memory rotating right (ROR in assembly langauge) or left (ROL) . This will occur if data types are being used which do not necessarily match, eg. a signed value entering an unsigned data type or if the number of bits is different in one variable to another.
Data being lost due to an unsigned value entering a signed variable. Outcomes are 1 bit being lost because it will be used to determine negative or positive, or at extremes if twos complement takes place the number will become inverted in meaning, look for twos complement on wikipedia.
Also see how memory should be cleared/assigned before use. http://www.cprogramming.com/tutorial/memory_debugging_parallel_inspector.html
How would I do a matrix multiplication in cpp format that would after be compiled into a mex file?
My normal matrix multiplication in a Matlab script is as follow:
cMatrix = (1 / r) * pfMatrix * wcMatrix; %here pfMatrix is 2x3 and wcMatrix is 3x8
% Hence cMatrix is 2x8
% r is a scalar
The pfMatrix, wcMatrix and r are declared correctly in the cpp file and they have the same values as in the script. However cMatrix doesn't give me the same results. Here the implementation of the Matrix multiplication in the cpp :
int i, n, j;
for (i = 0; i<1; i++)
{
for (n = 0; n<7; n++)
{
for (j = 0; j<2; j++)
{
d->cMatrix[i][n] += (d->pfMatrix[i][j]) * (d->wcMatrix[j][n]);
}
d->cMatrix[i][n] = (1 / d->r) * d->cMatrix[i][n];
}
}
Edit:
I modified the loop following Ben Voigt answer. The results in cMatrix are still not identical to the one calculated from the Matlab script.
For example :
pfMatrix = [7937.91049469652,0,512;0,7933.81033431703,384];
wcMatrix = [-0.880633810389421,-1.04063381038942,-1.04063381038942,-0.880633810389421,-0.815633810389421,-1.10563381038942,-1.10563381038942,-0.815633810389421;-0.125,-0.125,0.125,0.125,-0.29,-0.29,0.29,0.29;100,100,100,100,100,100,100,100];
r = 100;
In this case, cMatrix(1,1) is :
(pfMatrix(1,1)*wcMatrix(1,1) + pfMatrix(1,2)*wcMatrix(2,1) + pfMatrix(1,3)*wcMatrix(3,1)) / r = 442.09
However, with the mex file the equivalent result is 959.
Edit #2:
I found the error in an element of pfMatrix that was not declared correctly (missing a division by 2). So the answer of Ben Voigt is working correctly. However, there is still a slight difference between the two results (Matlab script gives 442 and the mex gives 447, could it be a results of different data type?).
Edit #3:
Found the error and it was not related with the matrix multiplication loop.
Using your result matrix as scratch space is not a great idea. The compiler has to worry about aliasing, which means it can't optimize.
Try an explicit working variable, which also provides a convenient place to zero it:
for (int i = 0; i < 2; ++i) {
for (int n = 0; n < 8; ++n) {
double accum = 0.0;
for (int j = 0; j < 3; ++j) {
accum += (d->pfMatrix[i][j]) * (d->wcMatrix[j][n]);
}
d->cMatrix[i][n] = accum / d->r;
}
}
Your ranges were also wrong, which I've fixed.
(Also note that good performance on large matrices requires banding to get good cache behavior, however that shouldn't be an issue on a product of this size.)
A multiplication between matrices must be in this way: A[m][n] * B[n][p] = R[m][p].
The conditions that you wrote in the for loops are not correct and doesn't respect the matrix dimensions.
Look also at the Eigen libraries, which are open-source and provide a simple way to do the matrix multiplications.
I am working on a project using OpenCV. I need to precisely crop out some objects from HD photos.
I'm using a quad tree to cut my photos in pieces and then I calculate the homogeneity of each quad to determine if a piece of the object is in the quad.
I apply some filters as Canny with different thresholds depending on the homogeneity of the quad.
I hope this description is understandable.
This algorithm works for certain kinds of objects but I'm stuck with some others.
Here some example of my problems: I would like a way to flatten my contours.
The first screenshot is a after using the canny filter and a floodfill. The second is the final mask result.
http://pastebin.com/91Pgrd2D
To achieve this result, I use cvFindContours() so I have the contours but I can't find a way to handle them like I want.
Maybe you could use some kind of an average filter to approximate the curve and then use AproxPoly with a small gradient to smooth it.
Here is a similar method:
void AverageFilter(CvSeq * contour, int buff_length)
{
int n = contour->total, i, j;
if (n > buff_length)
{
CvPoint2D32f* pnt;
float* sampleX = new float[buff_length];
float* sampleY = new float[buff_length];
pnt = (CvPoint2D32f*)cvGetSeqElem(contour, 0);
for (i = 0; i < buff_length; i++)
{
if (i >= buff_length / 2)
{
pnt = (CvPoint2D32f*)cvGetSeqElem(contour, i + 1 - buff_length / 2 );
}
sampleX[i] = pnt->x;
sampleY[i] = pnt->y;
}
float sumX = 0, sumY = 0;
for (i = 1; i < n; i++)
{
pnt = (CvPoint2D32f*)cvGetSeqElem(contour, i);
for (j = 0; j < buff_length; j++)
{
sumX += sampleX[j];
sumY += sampleY[j];
}
pnt->x = sumX / buff_length;
pnt->y = sumY / buff_length;
for (j = 0; j < buff_length - 1; j++)
{
sampleX[j] = sampleX[j+1];
sampleY[j] = sampleY[j+1];
}
if (i <= (n - buff_length / 2))
{
pnt = (CvPoint2D32f*)cvGetSeqElem(contour, i + buff_length / 2 + 1);
sampleX[buff_length - 1] = pnt->x;
sampleY[buff_length - 1] = pnt->y;
}
sumX = 0;
sumY = 0;
}
delete[] sampleX;
delete[] sampleY;
}
}
You give it the contour and the size of the buffer of points that you want to do the average on.
If you think the contour is too thick because some of the averaged points are bundled together too close, then that's where Aproxpoly comes in because it reduces the number of points.
But choose an appropriate gradient so you don't make it too edgy.
srcSeq = cvApproxPoly(srcSeq,sizeof(CvContour),storage, CV_POLY_APPROX_DP, x, 1);
Play around with 'x' to see how you get better results.