haader/haader.h

#ifndef HAADER_ILUCF4Z0
#define HAADER_ILUCF4Z0

#include <vector>
#include <iostream>

#include "image.h"

namespace haader {
    class ResponseFunction {
        friend class InverseResponseFunction;
        public:
            // Returns a pixel value (0-255) given the logarithm of a luminance value.
            int lookup(double value) const;

            // Write the lookup table in CSV-format to the given stream
            void to_csv_stream(std::ostream &stream) const;

        private:
            // minimum log of luminance value
            double m_min_value;

            // maximum log of luminance value
            double m_max_value;

            // Precomputed value:
            // 1.0 / (m_max_value - m_min_value)
            double m_recip_range;

            // Response function is implemented as a lookup table of with 256 values
            std::vector<int> m_lookup_table;
    };

    class InverseResponseFunction {
        friend class HdrImageStack;
        public:

            // Return logarithm of luminance given a pixel value (0-255)
            double lookup(int index) const;

            // The inverse of the lookup function:
            //   y == lookup(x)  ->  x == inverse_lookup(y)
            // O(n) complexity, proportional to size of lookup table.
            int inverse_lookup(double value) const;

            // Construct a ResponseFunction object that allows efficient O(1) inverse_lookup.
            // bins: Size of the lookup table for the response function
            ResponseFunction to_response_function(int bins=1024);

            // Write the lookup table in CSV-format to the given stream
            void to_csv_stream(std::ostream &stream) const;

        private:

            // Returns true if a monotonically increasing lookup table without missing values
            // can be constructed.
            bool repair();

            // Remove missing values by linear interpolation of neighboring values
            void fill_zeros();

            // Apply binomial low pass filter
            void low_pass_filter();

            // Returns true if values are monotonically increasing
            bool is_monotonic();

            // Inverse response function is implemented as a lookup table with 256 values
            std::vector<double> m_lookup_table;
    };

    // High Dynamic Range Image.
    // Stores the logarithm of the scene luminance for each pixel/channel in a high resolution.
    class HdrImage {
        friend class HdrImageStack;

        public:
            HdrImage();

            // Construct low dynamic range image with the logarithm of the scene luminance.
            Image get_log_image();

            // Construct low dynamic range image by a simulated exposure with a given response function.
            // exposure_time: Exposure time in seconds
            // compression:
            //   A value > 1.0 will compress the luminace values and give more contrast.
            //   A value < 1.0 will reduce the contrast but lower the risk of
            //     under-/overexposure in parts of the image.
            Image expose(double exposure_time, const ResponseFunction &rf, double compression=1.0);

        private:
            // Pixel values (logarithm of scene luminance). The channels are interleaved (RGBRGBRGB...).
            std::vector<double> m_image_data;

            // Width in pixels
            unsigned int m_width;

            // Height in pixels
            unsigned int m_height;

            // Number of channels (usually 3 for RGB images)
            unsigned int m_components;
    };

    // A stack of images/photographs of the same scene, with the same resolution but different exposure times.
    class HdrImageStack {
        public:
            HdrImageStack();

            // Read images from the given array of file paths
            bool read_from_files(char * const* file_paths, int number_of_paths);

            // Add an image from the given file path
            bool add_from_file_path(const char* file_path);

            bool get_average_image(Image &output);
            bool get_average_image_slow(Image &output);

            // Approximate the inverse response function from samples of random pixel locations.
            // num_samples: Number of samples
            // Returns true if a well-formed inverse response function could be found.
            bool get_inverse_response_function(InverseResponseFunction &output, unsigned int num_samples);

            // Return a HDR-image given an inverse response function
            HdrImage get_hdr_image(const InverseResponseFunction &invRespFunc);

        private:
            // Sort the images by exposure time
            void sort_by_exposure();

            // The images
            std::vector<Image> m_images;
    };

}

#endif // HAADER_ILUCF4Z0