prior_box_layer.cpp

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#include "../precomp.hpp"
#include "layers_common.hpp"
#include <float.h>
#include <algorithm>
#include <cmath>

namespace cv
{
namespace dnn
{

class PriorBoxLayerImpl : public PriorBoxLayer
{
public:
    bool getParameterDict(const LayerParams &params,
                          const std::string &parameterName,
                          DictValue& result)
    {
        if (!params.has(parameterName))
        {
            return false;
        }

        result = params.get(parameterName);
        return true;
    }

    template<typename T>
    T getParameter(const LayerParams &params,
                   const std::string &parameterName,
                   const size_t &idx=0,
                   const bool required=true,
                   const T& defaultValue=T())
    {
        DictValue dictValue;
        bool success = getParameterDict(params, parameterName, dictValue);
        if(!success)
        {
            if(required)
            {
                std::string message = _layerName;
                message += " layer parameter does not contain ";
                message += parameterName;
                message += " parameter.";
                CV_Error(Error::StsBadArg, message);
            }
            else
            {
                return defaultValue;
            }
        }
        return dictValue.get<T>(idx);
    }

    void getAspectRatios(const LayerParams &params)
    {
        DictValue aspectRatioParameter;
        bool aspectRatioRetieved = getParameterDict(params, "aspect_ratio", aspectRatioParameter);
        CV_Assert(aspectRatioRetieved);

        for (int i = 0; i < aspectRatioParameter.size(); ++i)
        {
            float aspectRatio = aspectRatioParameter.get<float>(i);
            bool alreadyExists = false;

            for (size_t j = 0; j < _aspectRatios.size(); ++j)
            {
                if (fabs(aspectRatio - _aspectRatios[j]) < 1e-6)
                {
                    alreadyExists = true;
                    break;
                }
            }
            if (!alreadyExists)
            {
                _aspectRatios.push_back(aspectRatio);
                if (_flip)
                {
                    _aspectRatios.push_back(1./aspectRatio);
                }
            }
        }
    }

    void getVariance(const LayerParams &params)
    {
        DictValue varianceParameter;
        bool varianceParameterRetrieved = getParameterDict(params, "variance", varianceParameter);
        CV_Assert(varianceParameterRetrieved);

        int varianceSize = varianceParameter.size();
        if (varianceSize > 1)
        {
            // Must and only provide 4 variance.
            CV_Assert(varianceSize == 4);

            for (int i = 0; i < varianceSize; ++i)
            {
                float variance = varianceParameter.get<float>(i);
                CV_Assert(variance > 0);
                _variance.push_back(variance);
            }
        }
        else
        {
            if (varianceSize == 1)
            {
                float variance = varianceParameter.get<float>(0);
                CV_Assert(variance > 0);
                _variance.push_back(variance);
            }
            else
            {
                // Set default to 0.1.
                _variance.push_back(0.1f);
            }
        }
    }

    PriorBoxLayerImpl(const LayerParams &params)
    {
        setParamsFrom(params);
        _minSize = getParameter<unsigned>(params, "min_size");
        CV_Assert(_minSize > 0);

        _flip = getParameter<bool>(params, "flip");
        _clip = getParameter<bool>(params, "clip");

        _aspectRatios.clear();
        _aspectRatios.push_back(1.);

        getAspectRatios(params);
        getVariance(params);

        _numPriors = _aspectRatios.size();

        _maxSize = -1;
        if (params.has("max_size"))
        {
            _maxSize = params.get("max_size").get<float>(0);
            CV_Assert(_maxSize > _minSize);

            _numPriors += 1;
        }
    }

    void allocate(const std::vector<Mat*> &inputs, std::vector<Mat> &outputs)
    {
        CV_Assert(inputs.size() == 2);

        _layerWidth = inputs[0]->size[3];
        _layerHeight = inputs[0]->size[2];

        _imageWidth = inputs[1]->size[3];
        _imageHeight = inputs[1]->size[2];

        _stepX = static_cast<float>(_imageWidth) / _layerWidth;
        _stepY = static_cast<float>(_imageHeight) / _layerHeight;

        // Since all images in a batch has same height and width, we only need to
        // generate one set of priors which can be shared across all images.
        int outNum = 1;
        // 2 channels. First channel stores the mean of each prior coordinate.
        // Second channel stores the variance of each prior coordinate.
        int outChannels = 2;
        _outChannelSize = _layerHeight * _layerWidth * _numPriors * 4;

        int outsz[] = { outNum, outChannels, (int)_outChannelSize };
        outputs[0].create(3, outsz, CV_32F);
    }

    void forward(std::vector<Mat*> &inputs, std::vector<Mat> &outputs)
    {
        (void)inputs; // to suppress unused parameter warning

        float* outputPtr = outputs[0].ptr<float>();

        // first prior: aspect_ratio = 1, size = min_size
        int idx = 0;
        for (size_t h = 0; h < _layerHeight; ++h)
        {
            for (size_t w = 0; w < _layerWidth; ++w)
            {
                _boxWidth = _boxHeight = _minSize;

                float center_x = (w + 0.5) * _stepX;
                float center_y = (h + 0.5) * _stepY;
                // xmin
                outputPtr[idx++] = (center_x - _boxWidth / 2.) / _imageWidth;
                // ymin
                outputPtr[idx++] = (center_y - _boxHeight / 2.) / _imageHeight;
                // xmax
                outputPtr[idx++] = (center_x + _boxWidth / 2.) / _imageWidth;
                // ymax
                outputPtr[idx++] = (center_y + _boxHeight / 2.) / _imageHeight;

                if (_maxSize > 0)
                {
                    // second prior: aspect_ratio = 1, size = sqrt(min_size * max_size)
                    _boxWidth = _boxHeight = sqrt(_minSize * _maxSize);
                    // xmin
                    outputPtr[idx++] = (center_x - _boxWidth / 2.) / _imageWidth;
                    // ymin
                    outputPtr[idx++] = (center_y - _boxHeight / 2.) / _imageHeight;
                    // xmax
                    outputPtr[idx++] = (center_x + _boxWidth / 2.) / _imageWidth;
                    // ymax
                    outputPtr[idx++] = (center_y + _boxHeight / 2.) / _imageHeight;
                }

                // rest of priors
                for (size_t r = 0; r < _aspectRatios.size(); ++r)
                {
                    float ar = _aspectRatios[r];
                    if (fabs(ar - 1.) < 1e-6)
                    {
                        continue;
                    }
                    _boxWidth = _minSize * sqrt(ar);
                    _boxHeight = _minSize / sqrt(ar);
                    // xmin
                    outputPtr[idx++] = (center_x - _boxWidth / 2.) / _imageWidth;
                    // ymin
                    outputPtr[idx++] = (center_y - _boxHeight / 2.) / _imageHeight;
                    // xmax
                    outputPtr[idx++] = (center_x + _boxWidth / 2.) / _imageWidth;
                    // ymax
                    outputPtr[idx++] = (center_y + _boxHeight / 2.) / _imageHeight;
                }
            }
        }
        // clip the prior's coordidate such that it is within [0, 1]
        if (_clip)
        {
            for (size_t d = 0; d < _outChannelSize; ++d)
            {
                outputPtr[d] = std::min<float>(std::max<float>(outputPtr[d], 0.), 1.);
            }
        }
        // set the variance.
        outputPtr = outputs[0].ptr<float>(0, 1);
        if(_variance.size() == 1)
        {
            Mat secondChannel(outputs[0].size[2], outputs[0].size[3], CV_32F, outputPtr);
            secondChannel.setTo(Scalar(_variance[0]));
        }
        else
        {
            int count = 0;
            for (size_t h = 0; h < _layerHeight; ++h)
            {
                for (size_t w = 0; w < _layerWidth; ++w)
                {
                    for (size_t i = 0; i < _numPriors; ++i)
                    {
                        for (int j = 0; j < 4; ++j)
                        {
                            outputPtr[count] = _variance[j];
                            ++count;
                        }
                    }
                }
            }
        }
    }

    size_t _layerWidth;
    size_t _layerHeight;

    size_t _imageWidth;
    size_t _imageHeight;

    size_t _outChannelSize;

    float _stepX;
    float _stepY;

    float _minSize;
    float _maxSize;

    float _boxWidth;
    float _boxHeight;

    std::vector<float> _aspectRatios;
    std::vector<float> _variance;

    bool _flip;
    bool _clip;

    size_t _numPriors;

    static const size_t _numAxes = 4;
    static const std::string _layerName;
};

const std::string PriorBoxLayerImpl::_layerName = std::string("PriorBox");

Ptr<PriorBoxLayer> PriorBoxLayer::create(const LayerParams &params)
{
    return Ptr<PriorBoxLayer>(new PriorBoxLayerImpl(params));
}

}
}