C++ OpenCV SVM Predict Not Working - c++

Question

Trying to create a functional SVM. I have 114 training images, 60 Positive/54 Negative, and 386 testing images for the SVM to predict against.
I read in the training image features to float like this:
trainingDataFloat[i][0] = trainFeatures.rows;
trainingDataFloat[i][1] = trainFeatures.cols;
And the same for the testing images too:
testDataFloat[i][0] = testFeatures.rows;
testDataFloat[i][2] = testFeatures.cols;
Then, using Micka's answer to this question, I turn the testDataFloat into a 1 Dimensional Array, and feed it to a Mat like this so to predict on the SVM:
float* testData1D = (float*)testDataFloat;
Mat testDataMat1D(height*width, 1, CV_32FC1, testData1D);
float testPredict = SVMmodel.predict(testDataMat1D);
Once this was all in place, there is the Debug Error of:
Sizes of input arguments do not match (the sample size is different from what has been used for training) in cvPreparePredictData
Looking at this post I found (Thanks to berak) that:
"all images (used in training & prediction) have to be the same size"
So I included a re-size function that would re-size the images to be all square at whatever size you wished (100x100, 200x200, 1000, 1000 etc.)
Run it again with the images re-sized to a new directory that the program now loads the images in from, and I get the exact same error as before of:
Sizes of input arguments do not match (the sample size is different from what has been used for training) in cvPreparePredictData
I just have no idea anymore on what to do. Why is it still throwing that error?
EDIT
I changed
Mat testDataMat1D(TestDFheight*TestDFwidth, 1, CV_32FC1, testData1D);
to
Mat testDataMat1D(1, TestDFheight*TestDFwidth, CV_32FC1, testData1D);
and placed the .predict inside the loop that the features are given to the float so that each image is given to the .predict individually because of this question. With the to int swapped so that .cols = 1 and .rows = TestDFheight*TestDFwidth the program seems to actually run, but then stops on image 160 (.exe has stopped working)... So that's a new concern.
EDIT 2
Added a simple
std::cout << testPredict;
To view the determined output of the SVM, and it seems to be positively matching everything until Image 160, where it stops running:

Answer 1

Please check your training and test feature vector.
I'm assuming your feature data is some form of cv::Mat containing features on each row.
In which case you want your training matrix to be a concatenation of each feature matrix from each image.
These line doesn't look right:
trainingDataFloat[i][0] = trainFeatures.rows;
trainingDataFloat[i][1] = trainFeatures.cols;
This is setting an element of a 2d matrix to the number of rows and columns in trainFeatures. This has nothing to do with the actual data that is in the trainFeatures matrix.
What are you trying to detect? If each image is a positive and negative example, then are you trying to detect something in an image? What are your features?
If you're trying to detect an object in the image on a per image basis, then you need a feature vector describing the whole image in one vector. In which case you'd do something like this with your training data:
int N; // Set to number of images you plan on using for training
int feature_size; // Set to the number of features extracted in each image. Should be constant across all images.
cv::Mat X = cv::Mat::zeros(N, feature_size, CV_32F); // Feature matrix
cv::Mat Y = cv::Mat::zeros(N, 1, CV_32F); // Label vector
// Now use a for loop to copy data into X and Y, Y = +1 for positive examples and -1 for negative examples
for(int i = 0; i < trainImages.size(); ++i)
{
X.row(i) = trainImages[i].features; // Where features is a cv::Mat row vector of size N of the extracted features
Y.row(i) = trainImages[i].isPositive ? 1:-1;
}
// Now train your cv::SVM on X and Y.