img/CImage.h

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/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          https://www.mrpt.org/                         |
   |                                                                        |
   | Copyright (c) 2005-2020, Individual contributors, see AUTHORS file     |
   | See: https://www.mrpt.org/Authors - All rights reserved.               |
   | Released under BSD License. See: https://www.mrpt.org/License          |
   +------------------------------------------------------------------------+ */
#pragma once

#include <mrpt/core/pimpl.h>
#include <mrpt/img/CCanvas.h>
#include <mrpt/img/TCamera.h>
#include <mrpt/img/TPixelCoord.h>
#include <mrpt/math/CMatrixDynamic.h>
#include <mrpt/math/CMatrixFixed.h>
#include <mrpt/serialization/CSerializable.h>

// Forwards decls:
// clang-format off
struct _IplImage;
using IplImage = struct _IplImage;
namespace cv { class Mat; }
namespace mrpt::io { class CStream; }
// clang-format on

// Add for declaration of mexplus::from template specialization
DECLARE_MEXPLUS_FROM(mrpt::img::CImage)

namespace mrpt::img
{
enum class PixelDepth : int32_t
{
    D8U = 0,
    D8S = 1,
    D16U = 2,
    D16S = 3,
    D32S = 4,
    D32F = 5,
    D64F = 6
};

/** Interpolation methods for images.
 *  Used for OpenCV related operations with images, but also with MRPT native
 * classes.
 * \sa mrpt::img::CMappedImage, CImage::scaleImage
 * \note These are numerically compatible to cv::InterpolationFlags
 * \ingroup mrpt_img_grp
 */
enum TInterpolationMethod
{
    IMG_INTERP_NN = 0,
    IMG_INTERP_LINEAR = 1,
    IMG_INTERP_CUBIC = 2,
    IMG_INTERP_AREA = 3
};

/** For use in mrpt::img::CImage */
enum TImageChannels : uint8_t
{
    CH_GRAY = 1,
    CH_RGB = 3
};

/** For usage in one of the CImage constructors */
enum ctor_CImage_ref_or_gray
{
    FAST_REF_OR_CONVERT_TO_GRAY = 1
};

/** Define kind of copies  */
enum copy_type_t
{
    /** Shallow copy: the copied object is a reference to the original one */
    SHALLOW_COPY = 0,
    /** Deep copy: the copied object has a duplicate of all data, becoming
       independent  */
    DEEP_COPY = 1
};

/** Used in mrpt::img::CImage */
class CExceptionExternalImageNotFound : public std::runtime_error
{
   public:
    CExceptionExternalImageNotFound(const std::string& s);
};

/** A class for storing images as grayscale or RGB bitmaps.
 * I/O is supported as:
 * - Binary dump using the CSerializable interface(<< and >> operators),
 *just as most objects in MRPT. This format is not compatible with any
 *standarized image format but it is fast.
 * - Saving/loading from files of different formats (bmp,jpg,png,...) using
 *the methods CImage::loadFromFile and CImage::saveToFile. See OpenCV for the
 *list of supported formats.
 * - Importing from an XPM array (.xpm file format) using CImage::loadFromXPM()
 * - Importing TGA images. See CImage::loadTGA()
 *
 *  How to create color/grayscale images:
 *  \code
 *    CImage  img1(width, height,  CH_GRAY );  // Grayscale image (8U1C)
 *    CImage  img2(width, height,  CH_RGB );  // RGB image (8U3C)
 *  \endcode
 *
 * Additional notes:
 * - The OpenCV `cv::Mat` format is used internally for compatibility with
 * all OpenCV functions. Use CImage::asCvMat() to retrieve it. Example:
 * \code
 * CImage  img;
 * ...
 * cv::Mat m = img.asCvMat()
 * \endcode
 * - By default, all images use unsigned 8-bit storage format for pixels (on
 *each channel), but it can be changed by flags in the constructor.
 * - An **external storage mode** can be enabled by calling
 *CImage::setExternalStorage, useful for storing large collections of image
 *objects in memory while loading the image data itself only for the relevant
 *images at any time. See CImage::forceLoad() and CImage::unload().
 * - Operator = and copy ctor make shallow copies. For deep copies, see
 * CImage::makeDeepCopy() or CImage(const CImage&, copy_type_t), e.g:
 * \code
 * CImage a(20, 10, CH_GRAY);
 * // Shallow copy ctor:
 * CImage b(a, mrpt::img::SHALLOW_COPY);
 * CImage c(a, mrpt::img::DEEP_COPY);
 * \endcode
 * - If you are interested in a smart pointer to an image, use:
 * \code
 * CImage::Ptr myImg = CImage::Create(); // optional ctor arguments
 * // or:
 * CImage::Ptr myImg = std::make_shared<CImage>(...);
 *  \endcode
 * - To set a CImage from an OpenCV `cv::Mat` use
 *CImage::CImage(cv::Mat,copy_type_t).
 *
 * Some functions are implemented in MRPT with highly optimized SSE2/SSE3
 *routines, in suitable platforms and compilers. To see the list of
 * optimizations refer to \ref sse_optimizations, falling back to default OpenCV
 *methods where unavailable.
 *
 * For computer vision functions that use CImage as its image data type,
 *see mrpt::vision.
 *
 * \sa mrpt::vision, mrpt::vision::CFeatureExtractor,
 *mrpt::vision::CImagePyramid, CSerializable, CCanvas
 * \ingroup mrpt_img_grp
 */
class CImage : public mrpt::serialization::CSerializable, public CCanvas
{
    DEFINE_SERIALIZABLE(CImage, mrpt::img)

    // This must be added for declaration of MEX-related functions
    DECLARE_MEX_CONVERSION

   public:
    /** @name Constructors & destructor
        @{ */

    /** Default constructor: initialize to empty image. It's an error trying to
     * access the image in such a state (except reading the image width/height,
     * which are both zero). Either call resize(), assign from another image,
     * load from disk, deserialize from an archive, etc. to properly initialize
     * the image.
     */
    CImage();

    /** Constructor for a given image size and type.
     *  Examples:
     *   \code
     *    CImage  img1(width, height,  CH_GRAY );  // Grayscale image (8U1C)
     *    CImage  img2(width, height,  CH_RGB );  // RGB image (8U3C)
     *   \endcode
     */
    CImage(
        unsigned int width, unsigned int height,
        TImageChannels nChannels = CH_RGB);

    /** Fast constructor of a grayscale version of another image, making a
     * **shallow copy** from the original image if it already was grayscale, or
     * otherwise creating a new grayscale image and converting the original
     * image into it.
     * Example of usage:
     *   \code
     *     void my_func(const CImage &in_img) {
     *        const CImage gray_img(in_img, FAST_REF_OR_CONVERT_TO_GRAY);
     *        // We can now operate on "gray_img" being sure it's in grayscale.
     *     }
     *   \endcode
     */
    inline CImage(const CImage& other_img, ctor_CImage_ref_or_gray)
    {
        if (other_img.isColor())
        {
            *this = CImage();
            other_img.grayscale(*this);
        }
        else
        {
            // shallow copy
            *this = other_img;
        }
    }

    /** Constructor from a cv::Mat image, making or not a deep copy of the data
     */
    CImage(const cv::Mat& img, copy_type_t copy_type);

    /** Constructor from another CImage, making or not a deep copy of the data
     */
    CImage(const CImage& img, copy_type_t copy_type);

    /** @} */

    /** @name Behavior-changing global flags
        @{ */

    /** By default, when storing images through the CSerializable interface,
     * grayscale images will be ZIP compressed if they are larger than 16Kb:
     * this flag can be turn on to disable ZIP compression and gain speed versus
     * occupied space.
     *  (Default = false) */
    static void DISABLE_ZIP_COMPRESSION(bool val);
    static bool DISABLE_ZIP_COMPRESSION();

    /** By default, when storing images through the CSerializable interface, RGB
     * images are JPEG-compressed to save space. If for some reason you prefer
     * storing RAW image data, disable this feature by setting this flag to
     * true.
     *  (Default = true) */
    static void DISABLE_JPEG_COMPRESSION(bool val);
    static bool DISABLE_JPEG_COMPRESSION();

    /** Unless DISABLE_JPEG_COMPRESSION=true, this sets the JPEG quality (range
     * 1-100) of serialized RGB images.
     *  (Default = 95) */
    static void SERIALIZATION_JPEG_QUALITY(int q);
    static int SERIALIZATION_JPEG_QUALITY();

    /** @} */

    /** @name Manipulate the image contents or size, various computer-vision
       methods (image filters, undistortion, etc.)
        @{ */

    /** Resets the image to the state after a default ctor. Accessing the image
     * after will throw an exception, unless it is formerly initialized somehow:
     * loading an image from disk, calling rezize(), etc. */
    void clear();

    /** Changes the size of the image, erasing previous contents (does NOT scale
     * its current content, for that, see scaleImage).
     *  - nChannels: Can be 3 for RGB images or 1 for grayscale images.
     * \sa scaleImage
     */
    void resize(
        std::size_t width, std::size_t height, TImageChannels nChannels,
        PixelDepth depth = PixelDepth::D8U);

    PixelDepth getPixelDepth() const;

    /** Scales this image to a new size, interpolating as needed, saving the new
     * image in a different output object, or operating in-place if
     * `out_img==this`. \sa resize, rotateImage
     */
    void scaleImage(
        CImage& out_img, unsigned int width, unsigned int height,
        TInterpolationMethod interp = IMG_INTERP_CUBIC) const;

    /** Rotates the image by the given angle around the given center point, with
     * an optional scale factor.
     * \sa resize, scaleImage
     */
    void rotateImage(
        CImage& out_img, double ang, unsigned int cx, unsigned int cy,
        double scale = 1.0) const;

    /** Changes the value of the pixel (x,y).
     *  Pixel coordinates starts at the left-top corner of the image, and start
     * in (0,0).
     *  The meaning of the parameter "color" depends on the implementation: it
     * will usually
     *   be a 24bit RGB value (0x00RRGGBB), but it can also be just a 8bit gray
     * level.
     *  This method must support (x,y) values OUT of the actual image size
     * without neither
     *   raising exceptions, nor leading to memory access errors.
     * \sa at, ptr
     */
    void setPixel(int x, int y, size_t color) override;

    // See CCanvas docs
    void line(
        int x0, int y0, int x1, int y1, const mrpt::img::TColor color,
        unsigned int width = 1, TPenStyle penStyle = psSolid) override;

    // See CCanvas docs
    void drawCircle(
        int x, int y, int radius,
        const mrpt::img::TColor& color = mrpt::img::TColor(255, 255, 255),
        unsigned int width = 1) override;

    // See CCanvas docs
    void drawImage(int x, int y, const mrpt::img::CImage& img) override;

    /** Equalize the image histogram, saving the new image in the given output
     * object.  \note RGB images are first converted to HSV color space, then
     * equalized for brightness (V) */
    void equalizeHist(CImage& out_img) const;

    /** Returns a new image scaled down to half its original size
     * \exception std::exception On odd size
     * \sa scaleDouble, scaleImage, scaleHalfSmooth
     */
    inline CImage scaleHalf(TInterpolationMethod interp) const
    {
        CImage ret;
        this->scaleHalf(ret, interp);
        return ret;
    }

    /** \overload
     *  \return true if an optimized SSE2/SSE3 version could be used. */
    bool scaleHalf(CImage& out_image, TInterpolationMethod interp) const;

    /** Returns a new image scaled up to double its original size.
     * \exception std::exception On odd size
     * \sa scaleHalf, scaleImage
     */
    inline CImage scaleDouble(TInterpolationMethod interp) const
    {
        CImage ret;
        this->scaleDouble(ret, interp);
        return ret;
    }

    //! \overload
    void scaleDouble(CImage& out_image, TInterpolationMethod interp) const;

    /** Update a part of this image with the "patch" given as argument.
     * The "patch" will be "pasted" at the (col,row) coordinates of this image.
     * \exception std::exception if patch pasted on the pixel (_row, _column)
     * jut out
     * of the image.
     * \sa extract_patch
     */
    void update_patch(
        const CImage& patch, const unsigned int col, const unsigned int row);

    /** Extract a patch from this image, saveing it into "patch" (its previous
     * contents will be overwritten).
     *  The patch to extract starts at (col,row) and has the given dimensions.
     * \sa update_patch
     */
    void extract_patch(
        CImage& patch, const unsigned int col = 0, const unsigned int row = 0,
        const unsigned int width = 1, const unsigned int height = 1) const;

    /** Computes the correlation coefficient (returned as val), between two
     *images
     *  This function use grayscale images only
     *  img1, img2 must be same size
     * (by AJOGD @ DEC-2006)
     */
    float correlate(
        const CImage& img2int, int width_init = 0, int height_init = 0) const;

    /** Computes the correlation matrix between this image and another one.
     *   This implementation uses the 2D FFT for achieving reduced computation
     * time.
     * \param in_img The "patch" image, which must be equal, or smaller than
     * "this" image. This function supports gray-scale (1 channel only) images.
     * \param u_search_ini The "x" coordinate of the search window.
     * \param v_search_ini The "y" coordinate of the search window.
     * \param u_search_size The width of the search window.
     * \param v_search_size The height of the search window.
     * \param out_corr The output for the correlation matrix, which will be
     * "u_search_size" x "v_search_size"
     * \param biasThisImg This optional parameter is a fixed "bias" value to be
     * substracted to the pixels of "this" image before performing correlation.
     * \param biasInImg This optional parameter is a fixed "bias" value to be
     * substracted to the pixels of "in_img" image before performing
     * correlation. Note: By default, the search area is the whole (this) image.
     * (by JLBC @ JAN-2006)
     * \sa cross_correlation
     */
    void cross_correlation_FFT(
        const CImage& in_img, math::CMatrixFloat& out_corr,
        int u_search_ini = -1, int v_search_ini = -1, int u_search_size = -1,
        int v_search_size = -1, float biasThisImg = 0,
        float biasInImg = 0) const;

    /** Optimize the brightness range of an image without using histogram
     * Only for one channel images.
     * \sa equalizeHist
     */
    void normalize();

    /** Flips the image vertically. \sa swapRB(), flipHorizontal() */
    void flipVertical();
    /** Flips the image horizontally \sa swapRB(), flipVertical() */
    void flipHorizontal();

    /** Swaps red and blue channels. */
    void swapRB();

    /** Undistort the image according to some camera parameters, and
     * returns an output undistorted image.
     * \param out_img The output undistorted image
     * \param cameraParams The input camera params (containing the intrinsic
     * and distortion parameters of the camera)
     * \note The intrinsic parameters (fx,fy,cx,cy) of the output image are the
     * same than in the input image.
     * \sa mrpt::vision::CUndistortMap
     */
    void undistort(
        CImage& out_img, const mrpt::img::TCamera& cameraParams) const;

    /** Rectify an image (undistorts and rectification) from a stereo pair
     * according to a pair of precomputed rectification maps
     * \param mapX, mapY   [IN] The pre-computed maps of the rectification
     * (should be computed beforehand)
     * \sa mrpt::vision::CStereoRectifyMap,
     * mrpt::vision::computeStereoRectificationMaps
     */
    void rectifyImageInPlace(void* mapX, void* mapY);

    /** Filter the image with a Median filter with a window size WxW, returning
     * the filtered image in out_img. For inplace operation, set out_img to
     * this. */
    void filterMedian(CImage& out_img, int W = 3) const;

    /** Filter the image with a Gaussian filter with a window size WxH,
     * replacing "this" image by the filtered one. For inplace operation, set
     * out_img to this. */
    void filterGaussian(
        CImage& out_img, int W = 3, int H = 3, double sigma = 1.0) const;

    /** Draw onto this image the detected corners of a chessboard. The length of
     * cornerCoords must be the product of the two check_sizes.
     *
     * \param cornerCoords [IN] The pixel coordinates of all the corners.
     * \param check_size_x [IN] The number of squares, in the X direction
     * \param check_size_y [IN] The number of squares, in the Y direction
     *
     * \return false if the length of cornerCoords is inconsistent (nothing is
     * drawn then).
     *
     * \sa mrpt::vision::findChessboardCorners
     */
    bool drawChessboardCorners(
        std::vector<TPixelCoordf>& cornerCoords, unsigned int check_size_x,
        unsigned int check_size_y, unsigned int lines_width = 1,
        unsigned int circles_radius = 4);

    /** Joins two images side-by-side horizontally. Both images must have the
     * same number of rows and be of the same type (i.e. depth and color mode)
     *
     * \param im1 [IN] The first image.
     * \param im2 [IN] The other image.
     */
    void joinImagesHorz(const CImage& im1, const CImage& im2);

    /** Compute the KLT response at a given pixel (x,y) - Only for grayscale
     * images (for efficiency it avoids converting to grayscale internally).
     *  See KLT_response() for more details on the internal
     * optimizations of this method, but this graph shows a general view:
     *  <img src="KLT_response_performance_SSE2.png" >
     */
    float KLT_response(
        const unsigned int x, const unsigned int y,
        const unsigned int half_window_size) const;

    /** @} */

    /** @name Copy, move & swap operations
        @{ */
    [[deprecated("Use makeShallowCopy() instead")]] inline void
        setFromImageReadOnly(const CImage& o)
    {
        *this = o.makeShallowCopy();
    }

    /** Returns a shallow copy of the original image */
    inline CImage makeShallowCopy() const
    {
        CImage r = *this;
        return r;
    }

    /** Returns a deep copy of this image.
     * If the image is externally-stored, there is no difference with a shallow
     * copy. \sa makeShallowCopy() */
    CImage makeDeepCopy() const;

    /** Copies from another image (shallow copy), and, if it is externally
     * stored, the image file will be actually loaded into memory in "this"
     * object. \sa operator = \exception CExceptionExternalImageNotFound If the
     * external image couldn't be loaded.
     */
    void copyFromForceLoad(const CImage& o);

    /** Moves an image from another object, erasing the origin image in the
     * process.
     * \sa operator =
     */
    [[deprecated("Use a=std::move(b); instead ")]] inline void copyFastFrom(
        CImage& o)
    {
        *this = std::move(o);
    }

    /** Assigns from an image in IplImage format */
    inline void loadFromIplImage(
        const IplImage* iplImage, copy_type_t c = DEEP_COPY)
    {
        internal_fromIPL(iplImage, c);
    }

    [[deprecated(
        "Prefer a ctor from a cv::Mat instead or use loadFromIplImage() "
        "explicitly specifying the kind of copy to be done")]] inline void
        setFromIplImageReadOnly(IplImage* iplImage)
    {
        internal_fromIPL(iplImage, SHALLOW_COPY);
    }

    /** Efficiently swap of two images */
    void swap(CImage& o);

    /** @} */

    /** @name Access to image contents (OpenCV data structure, and raw pixels)
        @{ */

    /** Makes a shallow or deep copy of this image into the provided cv::Mat.
     * \sa asCvMatRef */
    void asCvMat(cv::Mat& out_img, copy_type_t copy_type) const;

    template <typename CV_MAT>
    CV_MAT asCvMat(copy_type_t copy_type) const
    {
        CV_MAT ret;
        asCvMat(ret, copy_type);
        return ret;
    }

    /** Get a reference to the internal cv::Mat, which can be resized, etc. and
     * changes will be reflected in this CImage object. */
    cv::Mat& asCvMatRef();

    /** \overload  */
    const cv::Mat& asCvMatRef() const;

    /**  Access to pixels without checking boundaries - Use normally the ()
      operator better, which checks the coordinates.
      \sa CImage::operator()
      */
    [[deprecated("Use at<>(), ptr<>() or ptrLine() instead ")]] uint8_t*
        get_unsafe(
            unsigned int col, unsigned int row, uint8_t channel = 0) const;

    /**  Access to pixels without checking boundaries, and doing a
     * reinterpret_cast<> of the data as the given type.
     *\sa The CImage::operator() which does check for coordinate limits.
     */
    template <typename T>
    const T& at(
        unsigned int col, unsigned int row, unsigned int channel = 0) const
    {
        return *reinterpret_cast<const T*>(internal_get(col, row, channel));
    }
    /** \overload Non-const case */
    template <typename T>
    T& at(unsigned int col, unsigned int row, unsigned int channel = 0)
    {
        return *reinterpret_cast<T*>(internal_get(col, row, channel));
    }

    /** Returns a pointer to a given pixel, without checking for boundaries.
     *\sa The CImage::operator() which does check for coordinate limits.
     */
    template <typename T>
    const T* ptr(
        unsigned int col, unsigned int row, unsigned int channel = 0) const
    {
        return reinterpret_cast<const T*>(internal_get(col, row, channel));
    }
    /** \overload Non-const case */
    template <typename T>
    T* ptr(unsigned int col, unsigned int row, unsigned int channel = 0)
    {
        return reinterpret_cast<T*>(internal_get(col, row, channel));
    }

    /** Returns a pointer to the first pixel of the given line.\sa ptr, at */
    template <typename T>
    const T* ptrLine(unsigned int row) const
    {
        return reinterpret_cast<const T*>(internal_get(0, row, 0));
    }
    /** \overload Non-const case */
    template <typename T>
    T* ptrLine(unsigned int row)
    {
        return reinterpret_cast<T*>(internal_get(0, row, 0));
    }

    /** Returns the contents of a given pixel at the desired channel, in float
     * format: [0,255]->[0,1]
     *   The coordinate origin is pixel(0,0)=top-left corner of the image.
     * \exception std::exception On pixel coordinates out of bounds
     * \sa operator()
     */
    float getAsFloat(
        unsigned int col, unsigned int row, unsigned int channel) const;

    /** Returns the contents of a given pixel (for gray-scale images, in color
     * images the gray scale equivalent is computed for the pixel), in float
     * format: [0,255]->[0,1]
     *   The coordinate origin is pixel(0,0)=top-left corner of the image.
     * \exception std::exception On pixel coordinates out of bounds
     * \sa operator()
     */
    float getAsFloat(unsigned int col, unsigned int row) const;

    /** Returns a pointer to a given pixel information.
     *   The coordinate origin is pixel(0,0)=top-left corner of the image.
     * \exception std::exception On pixel coordinates out of bounds
     */
    unsigned char* operator()(
        unsigned int col, unsigned int row, unsigned int channel = 0) const;

    /** @} */

    /** @name Query image properties
        @{ */

    /** Returns the width of the image in pixels \sa getSize */
    size_t getWidth() const override;
    /** Returns the height of the image in pixels \sa getSize */
    size_t getHeight() const override;

    /** Return the size of the image \sa getWidth, getHeight */
    void getSize(TImageSize& s) const;
    /** Return the size of the image \sa getWidth, getHeight */
    inline TImageSize getSize() const
    {
        TImageSize ret;
        getSize(ret);
        return ret;
    }

    /** Returns the row stride of the image: this is the number of *bytes*
     * between two consecutive rows. You can access the pointer to the first row
     * with ptrLine(0)
     * \sa getSize, as, ptr, ptrLine */
    size_t getRowStride() const;

    /** As of mrpt 2.0.0, this returns either "GRAY" or "BGR". */
    std::string getChannelsOrder() const;

    /** Return the maximum pixel value of the image, as a float value in the
     * range [0,1]
     * \sa getAsFloat */
    float getMaxAsFloat() const;

    /** Returns true if the image is RGB, false if it is grayscale */
    bool isColor() const;

    /** Returns true if the object is in the state after default constructor */
    bool isEmpty() const;

    /** Returns true (as of MRPT v2.0.0, it's fixed) */
    bool isOriginTopLeft() const;

    /** Returns the number of channels, typically 1 (GRAY) or 3 (RGB)
     * \sa isColor
     */
    TImageChannels getChannelCount() const;

    /** Returns the image as a matrix with pixel grayscale values in the range
     * [0,1]. Matrix indexes in this order: M(row,column)
     *  \param doResize If set to true (default), the output matrix will be
     * always the size of the image at output. If set to false, the matrix will
     * be enlarged to the size of the image, but it will not be cropped if it
     * has room enough (useful for FFT2D,...)
     *  \param x_min The starting "x" coordinate to extract (default=0=the
     * first column)
     *  \param y_min The starting "y" coordinate to extract (default=0=the
     * first row)
     *  \param x_max The final "x" coordinate (inclusive) to extract
     * (default=-1=the last column)
     *  \param y_max The final "y" coordinate (inclusive) to extract
     * (default=-1=the last row)
     * \param normalize_01 Normalize the image values such that they fall in the
     * range [0,1] (default: true). If set to false, the matrix will hold
     * numbers in the range [0,255]. \sa setFromMatrix
     */
    void getAsMatrix(
        mrpt::math::CMatrixFloat& outMatrix, bool doResize = true,
        int x_min = 0, int y_min = 0, int x_max = -1, int y_max = -1,
        bool normalize_01 = true) const;

    /** \overload For uint8_t matrices [0, 255]. */
    void getAsMatrix(
        mrpt::math::CMatrix_u8& outMatrix, bool doResize = true, int x_min = 0,
        int y_min = 0, int x_max = -1, int y_max = -1) const;

    /** Returns the image as RGB matrices with pixel values in the range [0,1].
     * Matrix indexes in this order: M(row,column)
     *  \param doResize If set to true (default), the output matrix will be
     * always the size of the image at output. If set to false, the matrix will
     * be enlarged to the size of the image, but it will not be cropped if it
     * has room enough (useful for FFT2D,...)
     *  \param x_min The starting "x" coordinate to extract (default=0=the
     * first column)
     *  \param y_min The starting "y" coordinate to extract (default=0=the
     * first row)
     *  \param x_max The final "x" coordinate (inclusive) to extract
     * (default=-1=the last column)
     *  \param y_max The final "y" coordinate (inclusive) to extract
     * (default=-1=the last row)
     * \sa setFromRGBMatrices
     */
    void getAsRGBMatrices(
        mrpt::math::CMatrixFloat& outMatrixR,
        mrpt::math::CMatrixFloat& outMatrixG,
        mrpt::math::CMatrixFloat& outMatrixB, bool doResize = true,
        int x_min = 0, int y_min = 0, int x_max = -1, int y_max = -1) const;

    /** \overload For uint8_t matrices [0, 255]. */
    void getAsRGBMatrices(
        mrpt::math::CMatrix_u8& outMatrixR, mrpt::math::CMatrix_u8& outMatrixG,
        mrpt::math::CMatrix_u8& outMatrixB, bool doResize = true, int x_min = 0,
        int y_min = 0, int x_max = -1, int y_max = -1) const;

    /** Returns the image as a matrix, where the image is "tiled" (repeated)
     * the required number of times to fill the entire size of the matrix on
     * input.
     */
    void getAsMatrixTiled(mrpt::math::CMatrixFloat& outMatrix) const;

    /** @} */

    /** @name External storage-mode methods
        @{  */

    /**  By using this method the image is marked as referenced to an external
     * file, which will be loaded only under demand.
     *   A CImage with external storage does not consume memory until some
     * method trying to access the image is invoked (e.g. getWidth(),
     * isColor(),...)
     *   At any moment, the image can be unloaded from memory again by invoking
     * unload.
     *   An image becomes of type "external storage" only through calling
     * setExternalStorage. This property remains after serializing the object.
     *   File names can be absolute, or relative to the
     * CImage::getImagesPathBase() directory. Filenames staring with "X:\" or
     * "/"
     * are considered absolute paths.
     *   By calling this method the current contents of the image are NOT saved
     * to that file, because this method can be also called
     *    to let the object know where to load the image in case its contents
     * are required. Thus, for saving images in this format (not when loading)
     *    the proper order of commands should be:
     *   \code
     *   img.saveToFile( fileName );
     *   img.setExternalStorage( fileName );
     *   \endcode
     *
     *   \note Modifications to the memory copy of the image are not
     * automatically saved to disk.
     *  \sa unload, isExternallyStored
     */
    void setExternalStorage(const std::string& fileName) noexcept;

    /** By default, "."  \sa setExternalStorage */
    static const std::string& getImagesPathBase();
    static void setImagesPathBase(const std::string& path);

    /** See setExternalStorage(). */
    bool isExternallyStored() const noexcept { return m_imgIsExternalStorage; }
    /** Only if isExternallyStored() returns true. \sa
     * getExternalStorageFileAbsolutePath */
    inline std::string getExternalStorageFile() const noexcept
    {
        return m_externalFile;
    }

    /** Only if isExternallyStored() returns true. \sa getExternalStorageFile */
    void getExternalStorageFileAbsolutePath(std::string& out_path) const;

    /** Only if isExternallyStored() returns true. \sa getExternalStorageFile */
    inline std::string getExternalStorageFileAbsolutePath() const
    {
        std::string tmp;
        getExternalStorageFileAbsolutePath(tmp);
        return tmp;
    }

    /** For external storage image objects only, this method makes sure the
     * image is loaded in memory. Note that usually images are loaded on-the-fly
     * on first access and there's no need to call this.
     * \unload
     */
    inline void forceLoad() const { makeSureImageIsLoaded(); }
    /** For external storage image objects only, this method unloads the image
     * from memory (or does nothing if already unloaded).
     *  It does not need to be called explicitly, unless the user wants to save
     * memory for images that will not be used often.
     *  If called for an image without the flag "external storage", it is
     * simply ignored.
     * \sa setExternalStorage, forceLoad
     */
    void unload() const noexcept;

    /** @}  */
    // ================================================================

    // ================================================================
    /** @name Set, load & save methods
        @{  */

    /** Reads the image from raw pixels buffer in memory.
     */
    void loadFromMemoryBuffer(
        unsigned int width, unsigned int height, bool color,
        unsigned char* rawpixels, bool swapRedBlue = false);

    /** Reads a color image from three raw pixels buffers in memory.
     * bytesPerRow is the number of bytes per row per channel, i.e. the row
     * increment.
     */
    void loadFromMemoryBuffer(
        unsigned int width, unsigned int height, unsigned int bytesPerRow,
        unsigned char* red, unsigned char* green, unsigned char* blue);

    /** Set the image from a matrix, interpreted as grayscale intensity values,
     *in the range [0,1] (normalized=true) or [0,255] (normalized=false)
     *  Matrix indexes are assumed to be in this order: M(row,column)
     * \sa getAsMatrix
     */
    template <typename MAT>
    void setFromMatrix(const MAT& m, bool matrix_is_normalized = true)
    {
        MRPT_START
        const unsigned int lx = m.cols();
        const unsigned int ly = m.rows();
        this->resize(lx, ly, CH_GRAY);
        if (matrix_is_normalized)
        {  // Matrix: [0,1]
            for (unsigned int y = 0; y < ly; y++)
            {
                auto* pixels = ptrLine<uint8_t>(y);
                for (unsigned int x = 0; x < lx; x++)
                    (*pixels++) = static_cast<uint8_t>(m.coeff(y, x) * 255);
            }
        }
        else
        {  // Matrix: [0,255]
            for (unsigned int y = 0; y < ly; y++)
            {
                auto* pixels = ptrLine<uint8_t>(y);
                for (unsigned int x = 0; x < lx; x++)
                    (*pixels++) = static_cast<uint8_t>(m.coeff(y, x));
            }
        }
        MRPT_END
    }

    /** Set the image from RGB matrices, given the pixels in the range [0,1]
     * (normalized=true) or [0,255] (normalized=false)
     * Matrix indexes are assumed to be in this order: M(row,column)
     * \sa getAsRGBMatrices
     */
    template <typename MAT>
    void setFromRGBMatrices(
        const MAT& r, const MAT& g, const MAT& b,
        bool matrix_is_normalized = true)
    {
        MRPT_START
        makeSureImageIsLoaded();  // For delayed loaded images stored externally
        ASSERT_((r.size() == g.size()) && (r.size() == b.size()));
        const unsigned int lx = r.cols(), ly = r.rows();
        this->resize(lx, ly, CH_RGB);

        if (matrix_is_normalized)
        {  // Matrix: [0,1]
            for (unsigned int y = 0; y < ly; y++)
            {
                auto* pixels = ptrLine<uint8_t>(y);
                for (unsigned int x = 0; x < lx; x++)
                {
                    (*pixels++) = static_cast<uint8_t>(r.coeff(y, x) * 255);
                    (*pixels++) = static_cast<uint8_t>(g.coeff(y, x) * 255);
                    (*pixels++) = static_cast<uint8_t>(b.coeff(y, x) * 255);
                }
            }
        }
        else
        {  // Matrix: [0,255]
            for (unsigned int y = 0; y < ly; y++)
            {
                auto* pixels = ptrLine<uint8_t>(y);
                for (unsigned int x = 0; x < lx; x++)
                {
                    (*pixels++) = static_cast<uint8_t>(r.coeff(y, x));
                    (*pixels++) = static_cast<uint8_t>(g.coeff(y, x));
                    (*pixels++) = static_cast<uint8_t>(b.coeff(y, x));
                }
            }
        }
        MRPT_END
    }

    /** Reads the image from a binary stream containing a binary jpeg file.
     * \exception std::exception On pixel coordinates out of bounds
     */
    void loadFromStreamAsJPEG(mrpt::io::CStream& in);

    /** Load image from a file, whose format is determined from the extension
     * (internally uses OpenCV).
     * \param fileName The file to read from.
     * \param isColor Specifies colorness of the loaded image:
     *  - if >0, the loaded image is forced to be color 3-channel image;
     *  - if 0, the loaded image is forced to be grayscale;
     *  - if <0, the loaded image will be loaded as is (with number of channels
     * depends on the file).
     * The supported formats are:
     *
     * - Windows bitmaps - BMP, DIB;
     * - JPEG files - JPEG, JPG, JPE;
     * - Portable Network Graphics - PNG;
     * - Portable image format - PBM, PGM, PPM;
     * - Sun rasters - SR, RAS;
     * - TIFF files - TIFF, TIF.
     *
     * \return False on any error
     * \sa saveToFile, setExternalStorage,loadFromXPM, loadTGA
     */
    bool loadFromFile(const std::string& fileName, int isColor = -1);

    /** Loads a TGA true-color RGBA image as two CImage objects, one for the RGB
     * channels plus a separate gray-level image with A channel.
     * \return true on success
     */
    static bool loadTGA(
        const std::string& fileName, mrpt::img::CImage& out_RGB,
        mrpt::img::CImage& out_alpha);

    /** Loads the image from an XPM array, as #include'd from a ".xpm" file.
     * \param[in] swap_rb Swaps red/blue channels from loaded image. *Seems* to
     * be always needed, so it's enabled by default.
     * \sa loadFromFile
     * \return false on any error */
    bool loadFromXPM(const char* const* xpm_array, bool swap_rb = true);

    /** Save the image to a file, whose format is determined from the extension
     * (internally uses OpenCV).
     * \param fileName The file to write to.
     *
     * The supported formats are:
     *
     * - Windows bitmaps - BMP, DIB;
     * - JPEG files - JPEG, JPG, JPE;
     * - Portable Network Graphics - PNG;
     * - Portable image format - PBM, PGM, PPM;
     * - Sun rasters - SR, RAS;
     * - TIFF files - TIFF, TIF.
     *
     * \param jpeg_quality Only for JPEG files, the quality of the compression
     * in the range [0-100]. Larger is better quality but slower.
     * \note jpeg_quality is only effective if MRPT is compiled against OpenCV
     * 1.1.0 or newer.
     * \return False on any error
     * \sa loadFromFile
     */
    bool saveToFile(const std::string& fileName, int jpeg_quality = 95) const;

    /** Save image to binary stream as a JPEG (.jpg) compressed format.
     * \exception std::exception On number of rows or cols equal to zero or
     * other errors.
     * \sa saveToJPEG
     */
    void saveToStreamAsJPEG(
        mrpt::io::CStream& out, const int jpeg_quality = 95) const;

    /** @}  */
    // ================================================================

    // ================================================================
    /** @name Color/Grayscale conversion
        @{ */

    /** Returns a grayscale version of the image, or a shallow copy of itself if
     * it is already a grayscale image.
     */
    CImage grayscale() const;

    /** \overload.
     * In-place is supported by setting `ret=*this`.
     * \return true if SSE2 version has been run (or if the image was already
     * grayscale)
     */
    bool grayscale(CImage& ret) const;

    /** Returns a color (RGB) version of the grayscale image, or a shallow copy
     * of itself if it is already a color image.
     * \sa grayscale
     */
    CImage colorImage() const;

    /** \overload.
     * In-place is supported by setting `ret=*this`. */
    void colorImage(CImage& ret) const;

    /** @} */

    /** (DEPRECATED, DO NOT USE - Kept here only to interface opencv 2.4) */
    void getAsIplImage(IplImage* dest) const;

   protected:
    /** @name Data members
        @{ */

    /** PIMPL to cv::Mat object actually holding the image */
    struct Impl;
    mrpt::pimpl<Impl> m_impl;

    /**  Set to true only when using setExternalStorage.
     * \sa setExternalStorage
     */
    mutable bool m_imgIsExternalStorage{false};

    /** The file name of a external storage image. */
    mutable std::string m_externalFile;

    /** @} */

    /** Checks if the image is of type "external storage", and if so and not
     * loaded yet, load it.
     * \exception CExceptionExternalImageNotFound */
    void makeSureImageIsLoaded() const;
    uint8_t* internal_get(int col, int row, uint8_t channel = 0) const;
    void internal_fromIPL(const IplImage* iplImage, copy_type_t c);
};  // End of class
}  // namespace mrpt::img