在OpenCV中将图像转换为CvMat以训练神经网络

Question

I'm writing a program which uses OpenCv neural networks module along with C# and OpenCvSharp library. It must recognise the face of user, so in order to train the network, i need a set of samples. The problem is how to convert a sample image into array suitable for training. What i've got is 200x200 BitMap image, and network with 40000 input neurons, 200 hidden neurons and one output:

        CvMat layerSizes = Cv.CreateMat(3, 1, MatrixType.S32C1);
        layerSizes[0, 0] = 40000;
        layerSizes[1, 0] = 200;
        layerSizes[2, 0] = 1;
        Network = new CvANN_MLP(layerSizes,MLPActivationFunc.SigmoidSym,0.6,1);

So then I'm trying to convert BitMap image into CvMat array:

private void getTrainingMat(int cell_count, CvMat trainMAt, CvMat responses)
    {
        CvMat res = Cv.CreateMat(cell_count, 10, MatrixType.F32C1);//10 is a number of samples
        responses = Cv.CreateMat(10, 1, MatrixType.F32C1);//array of supposed outputs
        int counter = 0;
        foreach (Bitmap b in trainSet)
        {
            IplImage img = BitmapConverter.ToIplImage(b);
            Mat imgMat = new Mat(img);
            for (int i=0;i<imgMat.Height;i++)
            {
                for (int j = 0; j < imgMat.Width; j++)
                {
                    int val =imgMat.Get<int>(i, j);
                    res[counter, 0] = imgMat.Get<int>(i, j);
                }
                responses[i, 0] = 1;
            }
            trainMAt = res;
        }
    }

And then, when trying to train it, I've got this exception:

input training data should be a floating-point matrix withthe number of rows equal to the number of training samples and the number of columns equal to the size of 0-th (input) layer

Code for training:

        trainMAt = Cv.CreateMat(inp_layer_size, 10, MatrixType.F32C1);
        responses = Cv.CreateMat(inp_layer_size, 1, MatrixType.F32C1);
        getTrainingMat(inp_layer_size, trainMAt, responses);
        Network.Train(trainMAt, responses, new CvMat(),null, Parameters);

I'm new to OpenCV and I think I did something wrong in converting because of lack of understanding CvMat structure. Where is my error and is there any other way of transforming the bitmap?

Answer 1

With the number of rows equal to the number of training samples

That's 10 samples.

and the number of columns equal to the size of 0-th (input) layer

That's inp_layer_size.

trainMAt = Cv.CreateMat(10, inp_layer_size, MatrixType.F32C1);
responses = Cv.CreateMat(10, 1, MatrixType.F32C1); // 10 labels for 10 samples

I primarily do C++, so forgive me if I'm misunderstanding, but your pixel loop will need adapting in addition.

Your inner loop looks broken, as you assign to val , but never use it, and also never increment your counter.

In addition, in your outer loop assigning trainMAt = res; for every image doesn't seem like a very good idea.

I am certain you will get it to operate correctly, just keep in mind the fact that the goal is to flatten each image into a single row, so you end up with 10 rows and inp_layer_size columns.