mser 最大稳定极值区域(文字区域定位)算法 附完整C代码

mser 的全称:Maximally Stable Extremal Regions

第一次听说这个算法时，是来自当时部门的一个同事，

提及到他的项目用它来做文字区域的定位，对这个算法做了一些优化。

也就是中文车牌识别开源项目EasyPR的作者liuruoze,刘兄。

自那时起就有一块石头没放下，想要找个时间好好理理这个算法。

学习一些它的一些思路。

因为一般我学习算法的思路：3个做法，

第一步，编写demo示例。

第二步，进行算法移植或效果改进。

第三步，进行算法性能优化。

然后在这三个过程中，不断来回地验证，实测。

任何事情，一下子囫囵吞枣，容易呛到。

找了不少资料，mser这方面的资料还挺少。

比较不错的资料自然就是开源项目opencv以及VLFeat。

opencv用了太多依赖和封装，阅读代码非常费事。

VLFeat则友好得多。

嗯，花了点时间把mser从VLFeat抽离出来，并编写相应的测试用例。

代码注释比较详尽，写这个示例 demo 的时候，

来回翻阅官方文档无头绪，阅读代码以及注释才大致理清楚逻辑。

项目地址:https://github.com/cpuimage/mser

附完整代码:

/*
* Copyright (C) 2007-12 Andrea Vedaldi and Brian Fulkerson.
* All rights reserved.
* This file is part of the VLFeat library and is made available under
* the terms of the BSD license (see the COPYING file).
*/
#define MSER_DRIVER_VERSION 0.2

#define STB_IMAGE_STATIC
#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"
/* ref:https://github.com/nothings/stb/blob/master/stb_image.h */
#define TJE_IMPLEMENTATION
#include "tiny_jpeg.h"
/* ref:https://github.com/serge-rgb/TinyJPEG/blob/master/tiny_jpeg.h */

#include <stdlib.h>
#include <stdio.h>
/* 计时 */
#include <stdint.h>
#if   defined(__APPLE__)
#include <mach/mach_time.h>
#elif defined(_WIN32)
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#else /* __linux */
#include <time.h>
#ifndef  CLOCK_MONOTONIC  /* _RAW */
#define CLOCK_MONOTONIC CLOCK_REALTIME
#endif
#endif
static
uint64_t nanotimer()
{
    static int ever = ;
#if defined(__APPLE__)
    static mach_timebase_info_data_t frequency;
    if (!ever)
    {
        if (mach_timebase_info(&frequency) != KERN_SUCCESS)
        {
            return();
        }
        ever = ;
    }
    return;
#elif defined(_WIN32)
    static LARGE_INTEGER frequency;
    if (!ever)
    {
        QueryPerformanceFrequency(&frequency);
        ever = ;
    }
    LARGE_INTEGER t;
    QueryPerformanceCounter(&t);
    return((t.QuadPart * (uint64_t) 1e9) / frequency.QuadPart);
#else   /* __linux */
    struct timespec t;
    if (!ever)
    {
        if (clock_gettime(CLOCK_MONOTONIC, &spec) != )
        {
            return();
        }
        ever = ;
    }
    clock_gettime(CLOCK_MONOTONIC, &spec);
    return((t.tv_sec * (uint64_t) 1e9) + t.tv_nsec);
#endif
}

static double now()
{
    static uint64_t epoch = ;
    if (!epoch)
    {
        epoch = nanotimer();
    }
    return((nanotimer() - epoch) / 1e9);
};

double  calcElapsed(double start, double end)
{
    double took = -start;
    return(took + end);
}

unsigned char* loadImage(const char * filename, int * width, int * height, int * depth)
{
    unsigned char *output = stbi_load(filename, width, height, depth, );
    *depth = ;
    return(output);
}

bool saveJpeg(const char * filename, int width, int height, int depth, unsigned char* bits)
{
    if (!tje_encode_to_file(filename, width, height, depth, true, bits))
    {
        fprintf(stderr, "save JPEG fail.\n");
        return(false);
    }

    return(true);
}

/** @brief Maximum value
**
** Maximum value of the integer type ::unsigned char.
**/
#define MSER_PIX_MAXVAL 256

/** @brief MSER Filter
**
** The MSER filter computes the Maximally Stable Extremal Regions of
** an image.
**
** @sa @ref mser
**/
typedef struct _MserFilt MserFilt;

/** @brief MSER filter statistics */
typedef struct _MserStats MserStats;

/** @brief MSER filter statistics definition */
struct _MserStats
{
    int    num_extremal;           /**< number of extremal regions                                */
    int    num_unstable;           /**< number of unstable extremal regions                       */
    int    num_abs_unstable;       /**< number of regions that failed the absolute stability test */
    int    num_too_big;            /**< number of regions that failed the maximum size test       */
    int    num_too_small;          /**< number of regions that failed the minimum size test       */
    int    num_duplicates;         /**< number of regions that failed the duplicate test          */
};

/** @name Construction and Destruction
** @{
**/
MserFilt* mser_new(int ndims, int const* dims);

void mser_delete(MserFilt *f);

/** @} */

/** @name Processing
** @{
**/
void mser_process(MserFilt *f,
    unsigned char const *im);

void mser_ell_fit(MserFilt *f);

/** @} */

/** @name Retrieving data
** @{
**/
unsigned int mser_get_regions_num(MserFilt const *f);

unsigned int const* mser_get_regions(MserFilt const *f);

float const* mser_get_ell(MserFilt const *f);

unsigned int mser_get_ell_num(MserFilt const *f);

unsigned int mser_get_ell_dof(MserFilt const *f);

MserStats const* mser_get_stats(MserFilt const *f);

/** @} */

/** @name Retrieving parameters
** @{
**/
unsigned char mser_get_delta(MserFilt const *f);

float mser_get_min_area(MserFilt const *f);

float mser_get_max_area(MserFilt const *f);

float mser_get_max_variation(MserFilt const *f);

float mser_get_min_diversity(MserFilt const *f);

/** @} */

/** @name Setting parameters
** @{
**/
void mser_set_delta(MserFilt *f, unsigned char x);

void mser_set_min_area(MserFilt *f, float x);

void mser_set_max_area(MserFilt *f, float x);

void mser_set_max_variation(MserFilt *f, float x);

void mser_set_min_diversity(MserFilt *f, float x);

/** @} */

/* ====================================================================
*                                                   INLINE DEFINITIONS
* ================================================================== */

/** @internal
** @brief MSER accumulator data type
**
** This is a large integer type. It should be large enough to contain
** a number equal to the area (volume) of the image by the image
** width by the image height (for instance, if the image is a square
** of side 256, the maximum value is 256 x 256 x 256).
**/
typedef float mser_acc;

/** @internal @brief Basic region flag: null region */
#ifdef COMPILER_MSC
#define MSER_VOID_NODE ( (1ui64 << 32) - 1)
#else
#define MSER_VOID_NODE ( (1ULL << 32) - 1)
#endif

/* ----------------------------------------------------------------- */

/** @internal
** @brief MSER: basic region (declaration)
**
** Extremal regions and maximally stable extremal regions are
** instances of image regions.
**
** There is an image region for each pixel of the image. Each region
** is represented by an instance of this structure.  Regions are
** stored into an array in pixel order.
**
** Regions are arranged into a forest. MserReg::parent points to
** the parent node, or to the node itself if the node is a root.
** MserReg::parent is the index of the node in the node array
** (which therefore is also the index of the corresponding
** pixel). MserReg::height is the distance of the fartest leaf. If
** the node itself is a leaf, then MserReg::height is zero.
**
** MserReg::area is the area of the image region corresponding to
** this node.
**
** MserReg::region is the extremal region identifier. Not all
** regions are extremal regions however; if the region is NOT
** extremal, this field is set to ....
**/
struct _MserReg
{
    unsigned int    parent;         /**< points to the parent region.            */
    unsigned int    shortcut;       /**< points to a region closer to a root.    */
    unsigned int    height;         /**< region height in the forest.            */
    unsigned int    area;           /**< area of the region.                     */
};

/** @internal @brief MSER: basic region */
typedef struct _MserReg MserReg;

/* ----------------------------------------------------------------- */

/** @internal
** @brief MSER: extremal region (declaration)
**
** Extremal regions (ER) are extracted from the region forest. Each
** region is represented by an instance of this structure. The
** structures are stored into an array, in arbitrary order.
**
** ER are arranged into a tree. @a parent points to the parent ER, or
** to itself if the ER is the root.
**
** An instance of the structure represents the extremal region of the
** level set of intensity MserExtrReg::value and containing the
** pixel MserExtReg::index.
**
** MserExtrReg::area is the area of the extremal region and
** MserExtrReg::area_top is the area of the extremal region
** containing this region in the level set of intensity
** MserExtrReg::area + @c delta.
**
** MserExtrReg::variation is the relative area variation @c
** (area_top-area)/area.
**
** MserExtrReg::max_stable is a flag signaling whether this extremal
** region is also maximally stable.
**/
struct _MserExtrReg
{
    int        parent;         /**< index of the parent region                   */
    int        index;          /**< index of pivot pixel                         */
    unsigned char    value;          /**< value of pivot pixel                         */
    unsigned int    shortcut;       /**< shortcut used when building a tree           */
    unsigned int    area;           /**< area of the region                           */
    float        variation;      /**< rel. area variation                          */
    unsigned int    max_stable;     /**< max stable number (=0 if not maxstable)      */
};

/** @internal
** @brief MSER: extremal region */
typedef struct _MserExtrReg MserExtrReg;

/* ----------------------------------------------------------------- */

/** @internal
** @brief MSER filter
** @see @ref mser
**/
struct _MserFilt
{
    /** @name Image data and meta data @internal */
    /*@{*/
    int    ndims;          /**< number of dimensions                    */
    int    *dims;          /**< dimensions                              */
    int    nel;            /**< number of image elements (pixels)       */
    int    *subs;          /**< N-dimensional subscript                 */
    int    *dsubs;         /**< another subscript                       */
    int    *strides;       /**< strides to move in image data           */
                        /*@}*/

    unsigned int    *perm;  /**< pixel ordering                          */
    unsigned int    *joins; /**< sequence of join ops                    */
    int        njoins; /**< number of join ops                      */

                    /** @name Regions */
                    /*@{*/
    MserReg        *r;     /**< basic regions                           */
    MserExtrReg    *er;    /**< extremal tree                           */
    unsigned int    *mer;   /**< maximally stable extremal regions       */
    int        ner;    /**< number of extremal regions              */
    int        nmer;   /**< number of maximally stable extr. reg.   */
    int        rer;    /**< size of er buffer                       */
    int        rmer;   /**< size of mer buffer                      */
                    /*@}*/

                    /** @name Ellipsoids fitting */
                    /*@{*/
    float    *acc;           /**< moment accumulator.                    */
    float    *ell;           /**< ellipsoids list.                       */
    int    rell;           /**< size of ell buffer                     */
    int    nell;           /**< number of ellipsoids extracted         */
    int    dof;            /**< number of dof of ellipsoids.           */

                        /*@}*/

                        /** @name Configuration */
                        /*@{*/
    int    verbose;        /**< be verbose                             */
    int    delta;          /**< delta filter parameter                 */
    float    max_area;       /**< badness test parameter                 */
    float    min_area;       /**< badness test parameter                 */
    float    max_variation;  /**< badness test parameter                 */
    float    min_diversity;  /**< minimum diversity                      */
                            /*@}*/

    MserStats stats;        /** run statistic                           */
};

/* ----------------------------------------------------------------- */

/** @brief Get delta
** @param f MSER filter.
** @return value of @c delta.
**/
unsigned char
mser_get_delta(MserFilt const *f)
{
    return(f->delta);
}

/** @brief Set delta
** @param f MSER filter.
** @param x value of @c delta.
**/
void
mser_set_delta(MserFilt *f, unsigned char x)
{
    f->delta = x;
}

/* ----------------------------------------------------------------- */

/** @brief Get minimum diversity
** @param  f MSER filter.
** @return value of @c minimum diversity.
**/
float
mser_get_min_diversity(MserFilt const *f)
{
    return(f->min_diversity);
}

/** @brief Set minimum diversity
** @param f MSER filter.
** @param x value of @c minimum diversity.
**/
void
mser_set_min_diversity(MserFilt *f, float x)
{
    f->min_diversity = x;
}

/* ----------------------------------------------------------------- */

/** @brief Get statistics
** @param f MSER filter.
** @return statistics.
**/
MserStats const*
mser_get_stats(MserFilt const *f)
{
    return(&f->stats);
}

/* ----------------------------------------------------------------- */

/** @brief Get maximum region area
** @param f MSER filter.
** @return maximum region area.
**/
float
mser_get_max_area(MserFilt const *f)
{
    return(f->max_area);
}

/** @brief Set maximum region area
** @param f MSER filter.
** @param x maximum region area.
**/
void
mser_set_max_area(MserFilt *f, float x)
{
    f->max_area = x;
}

/* ----------------------------------------------------------------- */

/** @brief Get minimum region area
** @param f MSER filter.
** @return minimum region area.
**/
float
mser_get_min_area(MserFilt const *f)
{
    return(f->min_area);
}

/** @brief Set minimum region area
** @param f MSER filter.
** @param x minimum region area.
**/
void
mser_set_min_area(MserFilt *f, float x)
{
    f->min_area = x;
}

/* ----------------------------------------------------------------- */

/** @brief Get maximum region variation
** @param f MSER filter.
** @return maximum region variation.
**/
float
mser_get_max_variation(MserFilt const *f)
{
    return(f->max_variation);
}

/** @brief Set maximum region variation
** @param f MSER filter.
** @param x maximum region variation.
**/
void
mser_set_max_variation(MserFilt *f, float x)
{
    f->max_variation = x;
}

/* ----------------------------------------------------------------- */

/** @brief Get maximally stable extremal regions
** @param f MSER filter.
** @return array of MSER pivots.
**/
unsigned int const *
mser_get_regions(MserFilt const* f)
{
    return(f->mer);
}

/** @brief Get number of maximally stable extremal regions
** @param f MSER filter.
** @return number of MSERs.
**/
unsigned int
mser_get_regions_num(MserFilt const* f)
{
    return(f->nmer);
}

/* ----------------------------------------------------------------- */

/** @brief Get ellipsoids
** @param f MSER filter.
** @return ellipsoids.
**/
float const *
mser_get_ell(MserFilt const* f)
{
    return(f->ell);
}

/** @brief Get number of degrees of freedom of ellipsoids
** @param f MSER filter.
** @return number of degrees of freedom.
**/
unsigned int
mser_get_ell_dof(MserFilt const* f)
{
    return(f->dof);
}

/** @brief Get number of ellipsoids
** @param f MSER filter.
** @return number of ellipsoids
**/
unsigned int
mser_get_ell_num(MserFilt const* f)
{
    return(f->nell);
}

/*MSER */

/** -------------------------------------------------------------------
** @brief Advance N-dimensional subscript
**
** The function increments by one the subscript @a subs indexing an
** array the @a ndims dimensions @a dims.
**
** @param ndims number of dimensions.
** @param dims dimensions.
** @param subs subscript to advance.
**/

void adv(int ndims, int const *dims, int *subs)
{
    int d = ;
    while (d < ndims)
    {
        if (++subs[d] < dims[d])
            return;
        subs[d++] = ;
    }
}

/** -------------------------------------------------------------------
** @brief Climb the region forest to reach aa root
**
** The function climbs the regions forest @a r starting from the node
** @a idx to the corresponding root.
**
** To speed-up the operation, the function uses the
** MserReg::shortcut field to quickly jump to the root. After the
** root is reached, all the used shortcut are updated.
**
** @param r regions' forest.
** @param idx stating node.
** @return index of the reached root.
**/

unsigned int climb(MserReg* r, unsigned int idx)
{
    unsigned int    prev_idx = idx;
    unsigned int    next_idx;
    unsigned int    root_idx;

    /* move towards root to find it */
    while ()
    {
        /* next jump to the root */
        next_idx = r[idx].shortcut;

        /* recycle shortcut to remember how we came here */
        r[idx].shortcut = prev_idx;

        /* stop if the root is found */
        if (next_idx == idx)
            break;

        /* next guy */
        prev_idx = idx;
        idx = next_idx;
    }

    root_idx = idx;

    /* move backward to update shortcuts */
    while ()
    {
        /* get previously visited one */
        prev_idx = r[idx].shortcut;

        /* update shortcut to point to the new root */
        r[idx].shortcut = root_idx;

        /* stop if the first visited node is reached */
        if (prev_idx == idx)
            break;

        /* next guy */
        idx = prev_idx;
    }

    return(root_idx);
}

/** -------------------------------------------------------------------
** @brief Create a new MSER filter
**
** Initializes a new MSER filter for images of the specified
** dimensions. Images are @a ndims -dimensional arrays of dimensions
** @a dims.
**
** @param ndims number of dimensions.
** @param dims  dimensions.
**/

MserFilt*
mser_new(int ndims, int const* dims)
{
    MserFilt* f = (MserFilt *)calloc(sizeof(MserFilt), );

    f->ndims = ndims;
    f->dims = (int *)malloc(sizeof(int) * ndims);
    f->subs = (int *)malloc(sizeof(int) * ndims);
    f->dsubs = (int *)malloc(sizeof(int) * ndims);
    f->strides = (int *)malloc(sizeof(int) * ndims);
    /* shortcuts */
    if (f->dims != NULL && f->subs != NULL && f->dsubs != NULL && f->strides != NULL)
    {
        int k = ;

        /* copy dims to f->dims */
        memcpy(f->dims, dims, sizeof(int) * ndims);

        /* compute strides to move into the N-dimensional image array */
        f->strides[] = ;
        for (k = ; k < ndims; ++k)
        {
            f->strides[k] = f->strides[k - ] * dims[k - ];
        }

        /* total number of pixels */
        f->nel = f->strides[ndims - ] * dims[ndims - ];

        /* dof of ellipsoids */
        f->dof = ndims * (ndims + ) /  + ndims;

        /* more buffers */
        f->perm = (unsigned int *)malloc(sizeof(unsigned int) * f->nel);
        f->joins = (unsigned int *)malloc(sizeof(unsigned int) * f->nel);
        f->r = (MserReg *)malloc(sizeof(MserReg) * f->nel);

        f->er = ;
        f->rer = ;
        f->mer = ;
        f->rmer = ;
        f->ell = ;
        f->rell = ;

        /* other parameters */
        f->delta = ;
        f->max_area = 0.75f;
        f->min_area = 3.0f / f->nel;
        f->max_variation = 0.25f;
        f->min_diversity = 0.2f;
    }
    return(f);
}

/** -------------------------------------------------------------------
** @brief Delete MSER filter
**
** The function releases the MSER filter @a f and all its resources.
**
** @param f MSER filter to be deleted.
**/

void
mser_delete(MserFilt* f)
{
    if (f)
    {
        if (f->acc)
            free(f->acc);
        if (f->ell)
            free(f->ell);

        if (f->er)
            free(f->er);
        if (f->r)
            free(f->r);
        if (f->joins)
            free(f->joins);
        if (f->perm)
            free(f->perm);

        if (f->strides)
            free(f->strides);
        if (f->dsubs)
            free(f->dsubs);
        if (f->subs)
            free(f->subs);
        if (f->dims)
            free(f->dims);

        if (f->mer)
            free(f->mer);
        free(f);
    }
}

#define MAX( x, y ) ( ( (x) > (y) ) ? (x) : (y) )

/** -------------------------------------------------------------------
** @brief Process image
**
** The functions calculates the Maximally Stable Extremal Regions
** (MSERs) of image @a im using the MSER filter @a f.
**
** The filter @a f must have been initialized to be compatible with
** the dimensions of @a im.
**
** @param f MSER filter.
** @param im image data.
**/

void
mser_process(MserFilt* f, unsigned char const* im)
{
    /* shortcuts */
    unsigned int    nel = f->nel;
    unsigned int    *perm = f->perm;
    unsigned int    *joins = f->joins;
    int        ndims = f->ndims;
    int        *dims = f->dims;
    int        *subs = f->subs;
    int        *dsubs = f->dsubs;
    int        *strides = f->strides;
    MserReg        *r = f->r;
    MserExtrReg    *er = f->er;
    unsigned int    *mer = f->mer;
    int        delta = f->delta;

    int    njoins = ;
    int    ner = ;
    int    nmer = ;
    int    nbig = ;
    int    nsmall = ;
    int    nbad = ;
    int    ndup = ;

    int i, j, k;

    /* delete any previosuly computed ellipsoid */
    f->nell = ;

    /* -----------------------------------------------------------------
    *                                          Sort pixels by intensity
    * -------------------------------------------------------------- */

    {
        unsigned int buckets[MSER_PIX_MAXVAL];

        /* clear buckets */
        memset(buckets, , sizeof(unsigned int) * MSER_PIX_MAXVAL);

        /* compute bucket size (how many pixels for each intensity
        * value) */
        for (i = ; i < (int)nel; ++i)
        {
            unsigned char v = im[i];
            ++buckets[v];
        }

        /* cumulatively add bucket sizes */
        for (i = ; i < MSER_PIX_MAXVAL; ++i)
        {
            buckets[i] += buckets[i - ];
        }

        /* empty buckets computing pixel ordering */
        for (i = nel; i >= ; )
        {
            unsigned char    v = im[--i];
            unsigned int    j = --buckets[v];
            perm[j] = i;
        }
    }

    /* initialize the forest with all void nodes */
    for (i = ; i < (int)nel; ++i)
    {
        r[i].parent = MSER_VOID_NODE;
    }

    /* -----------------------------------------------------------------
    *                        Compute regions and count extremal regions
    * -------------------------------------------------------------- */

    /*
    * In the following:
    * idx    : index of the current pixel
    * val    : intensity of the current pixel
    * r_idx  : index of the root of the current pixel
    * n_idx  : index of the neighbors of the current pixel
    * nr_idx : index of the root of the neighbor of the current pixel
    */

    /* process each pixel by increasing intensity */
    for (i = ; i < (int)nel; ++i)
    {
        /* pop next node xi */
        unsigned int    idx = perm[i];
        unsigned char    val = im[idx];
        unsigned int    r_idx;

        /* add the pixel to the forest as a root for now */
        r[idx].parent = idx;
        r[idx].shortcut = idx;
        r[idx].area = ;
        r[idx].height = ;

        r_idx = idx;

        /* convert the index IDX into the subscript SUBS; also initialize
        * DSUBS to (-1,-1,...,-1) */
        {
            unsigned int temp = idx;
            for (k = ndims - ; k >= ; --k)
            {
                dsubs[k] = -;
                subs[k] = temp / strides[k];
                temp = temp % strides[k];
            }
        }

        /* examine the neighbors of the current pixel */
        while ()
        {
            unsigned int    n_idx = ;
            int        good = ;

            /*
            * Compute the neighbor subscript as NSUBS+SUB, the
            * corresponding neighbor index NINDEX and check that the
            * neighbor is within the image domain.
            */
            for (k = ; k < ndims && good; ++k)
            {
                int temp = dsubs[k] + subs[k];
                good &= ( <= temp) && (temp < dims[k]);
                n_idx += temp * strides[k];
            }

            /*
            * The neighbor should be processed if the following conditions
            * are met:
            * 1. The neighbor is within image boundaries.
            * 2. The neighbor is indeed different from the current node
            * (the opposite happens when DSUB=(0,0,...,0)).
            * 3. The neighbor is already in the forest, meaning that it has
            * already been processed.
            */
            if (good &&
                n_idx != idx &&
                r[n_idx].parent != MSER_VOID_NODE)
            {
                unsigned char    nr_val = ;
                unsigned int    nr_idx = ;
                int        hgt = r[r_idx].height;
                int        n_hgt = r[nr_idx].height;

                /*
                * Now we join the two subtrees rooted at
                * R_IDX = ROOT(  IDX)
                * NR_IDX = ROOT(N_IDX).
                * Note that R_IDX = ROOT(IDX) might change as we process more
                * neighbors, so we need keep updating it.
                */

                r_idx = climb(r, idx);
                nr_idx = climb(r, n_idx);

                /*
                * At this point we have three possibilities:
                * (A) ROOT(IDX) == ROOT(NR_IDX). In this case the two trees
                * have already been joined and we do not do anything.
                * (B) I(ROOT(IDX)) == I(ROOT(NR_IDX)). In this case the pixel
                * IDX is extending an extremal region with the same
                * intensity value. Since ROOT(NR_IDX) will NOT be an
                * extremal region of the full image, ROOT(IDX) can be
                * safely added as children of ROOT(NR_IDX) if this
                * reduces the height according to the union rank
                * heuristic.
                * (C) I(ROOT(IDX)) > I(ROOT(NR_IDX)). In this case the pixel
                * IDX is starting a new extremal region. Thus ROOT(NR_IDX)
                * WILL be an extremal region of the final image and the
                * only possibility is to add ROOT(NR_IDX) as children of
                * ROOT(IDX), which becomes parent.
                */

                if (r_idx != nr_idx) /* skip if (A) */

                {
                    nr_val = im[nr_idx];

                    if (nr_val == val && hgt < n_hgt)
                    {
                        /* ROOT(IDX) becomes the child */
                        r[r_idx].parent = nr_idx;
                        r[r_idx].shortcut = nr_idx;
                        r[nr_idx].area += r[r_idx].area;
                        r[nr_idx].height = MAX(n_hgt, hgt + );

                        joins[njoins++] = r_idx;
                    }
                    else {
                        /* cases ROOT(IDX) becomes the parent */
                        r[nr_idx].parent = r_idx;
                        r[nr_idx].shortcut = r_idx;
                        r[r_idx].area += r[nr_idx].area;
                        r[r_idx].height = MAX(hgt, n_hgt + );

                        joins[njoins++] = nr_idx;

                        /* count if extremal */
                        if (nr_val != val)
                            ++ner;
                    }       /* check b vs c */
                }               /* check a vs b or c */
            }                       /* neighbor done */

                                    /* move to next neighbor */
            k = ;
            while (++dsubs[k] > )
            {
                dsubs[k++] = -;
                if (k == ndims)
                    goto done_all_neighbors;
            }
        } /* next neighbor */
    done_all_neighbors:;
    }        /* next pixel */

             /* the last root is extremal too */
    ++ner;

    /* save back */
    f->njoins = njoins;

    f->stats.num_extremal = ner;

    /* -----------------------------------------------------------------
    *                                          Extract extremal regions
    * -------------------------------------------------------------- */

    /*
    * Extremal regions are extracted and stored into the array ER.  The
    * structure R is also updated so that .SHORTCUT indexes the
    * corresponding extremal region if any (otherwise it is set to
    * VOID).
    */

    /* make room */
    if (f->rer < ner)
    {
        if (er)
            free(er);
        f->er = er = (MserExtrReg *)malloc(sizeof(MserExtrReg) * ner);
        f->rer = ner;
    }
    ;

    /* save back */
    f->nmer = ner;

    /* count again */
    ner = ;

    /* scan all regions Xi */
    if (er != NULL)
    {
        for (i = ; i < (int)nel; ++i)
        {
            /* pop next node xi */
            unsigned int idx = perm[i];

            unsigned char    val = im[idx];
            unsigned int    p_idx = r[idx].parent;
            unsigned char    p_val = im[p_idx];

            /* is extremal ? */
            int is_extr = (p_val > val) || idx == p_idx;

            if (is_extr)
            {
                /* if so, add it */
                er[ner].index = idx;
                er[ner].parent = ner;
                er[ner].value = im[idx];
                er[ner].area = r[idx].area;

                /* link this region to this extremal region */
                r[idx].shortcut = ner;

                /* increase count */
                ++ner;
            }
            else {
                /* link this region to void */
                r[idx].shortcut = MSER_VOID_NODE;
            }
        }
    }

    /* -----------------------------------------------------------------
    *                                   Link extremal regions in a tree
    * -------------------------------------------------------------- */

    for (i = ; i < ner; ++i)
    {
        unsigned int idx = er[i].index;

        do
        {
            idx = r[idx].parent;
        } while (r[idx].shortcut == MSER_VOID_NODE);

        er[i].parent = r[idx].shortcut;
        er[i].shortcut = i;
    }

    /* -----------------------------------------------------------------
    *                            Compute variability of +DELTA branches
    * -------------------------------------------------------------- */

    /* For each extremal region Xi of value VAL we look for the biggest
    * parent that has value not greater than VAL+DELTA. This is dubbed
    * `top parent'. */

    for (i = ; i < ner; ++i)
    {
        /* Xj is the current region the region and Xj are the parents */
        int    top_val = er[i].value + delta;
        int    top = er[i].shortcut;

        /* examine all parents */
        while ()
        {
            int    next = er[top].parent;
            int    next_val = er[next].value;

            /* Break if:
            * - there is no node above the top or
            * - the next node is above the top value.
            */
            if (next == top || next_val > top_val)
                break;

            /* so next could be the top */
            top = next;
        }

        /* calculate branch variation */
        {
            int    area = er[i].area;
            int    area_top = er[top].area;
            er[i].variation = (float)(area_top - area) / area;
            er[i].max_stable = ;
        }

        /* Optimization: since extremal regions are processed by
        * increasing intensity, all next extremal regions being processed
        * have value at least equal to the one of Xi. If any of them has
        * parent the parent of Xi (this comprises the parent itself), we
        * can safely skip most intermediate node along the branch and
        * skip directly to the top to start our search. */
        {
            int    parent = er[i].parent;
            int    curr = er[parent].shortcut;
            er[parent].shortcut = MAX(top, curr);
        }
    }

    /* -----------------------------------------------------------------
    *                                  Select maximally stable branches
    * -------------------------------------------------------------- */

    nmer = ner;
    for (i = ; i < ner; ++i)
    {
        unsigned int    parent = er[i].parent;
        unsigned char    val = er[i].value;
        float        var = er[i].variation;
        unsigned char    p_val = er[parent].value;
        float        p_var = er[parent].variation;
        unsigned int    loser;

        /*
        * Notice that R_parent = R_{l+1} only if p_val = val + 1. If not,
        * this and the parent region coincide and there is nothing to do.
        */
        if (p_val > val + )
            continue;

        /* decide which one to keep and put that in loser */
        if (var < p_var)
            loser = parent;
        else loser = i;

        /* make loser NON maximally stable */
        if (er[loser].max_stable)
        {
            --nmer;
            er[loser].max_stable = ;
        }
    }

    f->stats.num_unstable = ner - nmer;

    /* -----------------------------------------------------------------
    *                                                 Further filtering
    * -------------------------------------------------------------- */

    /* It is critical for correct duplicate detection to remove regions
    * from the bottom (smallest one first).                          */
    {
        float    max_area = (float)f->max_area * nel;
        float    min_area = (float)f->min_area * nel;
        float    max_var = (float)f->max_variation;
        float    min_div = (float)f->min_diversity;

        /* scan all extremal regions (intensity value order) */
        for (i = ner - ; i >= 0L; --i)
        {
            /* process only maximally stable extremal regions */
            if (!er[i].max_stable)
                continue;

            if (er[i].variation >= max_var)
            {
                ++nbad;   goto remove;
            }
            if (er[i].area > max_area)
            {
                ++nbig;   goto remove;
            }
            if (er[i].area < min_area)
            {
                ++nsmall; goto remove;
            }

            /*
            * Remove duplicates
            */
            if (min_div < 1.0)
            {
                unsigned int    parent = er[i].parent;
                int        area, p_area;
                float        div;

                /* check all but the root mser */
                if ((int)parent != i)
                {
                    /* search for the maximally stable parent region */
                    while (!er[parent].max_stable)
                    {
                        unsigned int next = er[parent].parent;
                        if (next == parent)
                            break;
                        parent = next;
                    }

                    /* Compare with the parent region; if the current and parent
                    * regions are too similar, keep only the parent. */
                    area = er[i].area;
                    p_area = er[parent].area;
                    div = (float)(p_area - area) / (float)p_area;

                    if (div < min_div)
                    {
                        ++ndup; goto remove;
                    }
                } /* remove dups end */
            }
            continue;
        remove:
            er[i].max_stable = ;
            --nmer;
        }         /* check next region */

        f->stats.num_abs_unstable = nbad;
        f->stats.num_too_big = nbig;
        f->stats.num_too_small = nsmall;
        f->stats.num_duplicates = ndup;
    }

    /* -----------------------------------------------------------------
    *                                                   Save the result
    * -------------------------------------------------------------- */

    /* make room */
    if (f->rmer < nmer)
    {
        if (mer)
            free(mer);
        f->mer = mer = (unsigned int *)malloc(sizeof(unsigned int) * nmer);
        f->rmer = nmer;
    }

    /* save back */
    f->nmer = nmer;

    j = ;
    if (er != NULL && mer != NULL)
    {
        for (i = ; i < ner; ++i)
        {
            if (er[i].max_stable)
                mer[j++] = er[i].index;
        }
    }
}

/** -------------------------------------------------------------------
** @brief Fit ellipsoids
**
** @param f MSER filter.
**
** @sa @ref mser-ell
**/

void
mser_ell_fit(MserFilt* f)
{
    /* shortcuts */
    int        nel = f->nel;
    int        dof = f->dof;
    int        *dims = f->dims;
    int        ndims = f->ndims;
    int        *subs = f->subs;
    int        njoins = f->njoins;
    unsigned int    *joins = f->joins;
    MserReg        *r = f->r;
    unsigned int    *mer = f->mer;
    int        nmer = f->nmer;
    mser_acc    *acc = f->acc;
    mser_acc    *ell = f->ell;

    int d, index, i, j;

    /* already fit ? */
    if (f->nell == f->nmer)
        return;

    /* make room */
    if (f->rell < f->nmer)
    {
        if (f->ell)
            free(f->ell);
        f->ell = (float *)malloc(sizeof(float) * f->nmer * f->dof);
        f->rell = f->nmer;
    }

    if (f->acc == )
    {
        f->acc = (float *)malloc(sizeof(float) * f->nel);
    }

    acc = f->acc;
    ell = f->ell;

    /* -----------------------------------------------------------------
    *                                                 Integrate moments
    * -------------------------------------------------------------- */

    /* for each dof */
    for (d = ; d < f->dof; ++d)
    {
        /* start from the upper-left pixel (0,0,...,0) */
        memset(subs, , sizeof(int) * ndims);

        /* step 1: fill acc pretending that each region has only one pixel */
        if (d < ndims)
        {
            /* 1-order ................................................... */

            for (index = ; index < nel; ++index)
            {
                acc[index] = (float)subs[d];
                adv(ndims, dims, subs);
            }
        }
        else {
            /* 2-order ................................................... */

            /* map the dof d to a second order moment E[x_i x_j] */
            i = d - ndims;
            j = ;
            while (i > j)
            {
                i -= j + ;
                j++;
            }
            /* initialize acc with  x_i * x_j */
            for (index = ; index < nel; ++index)
            {
                acc[index] = (float)(subs[i] * subs[j]);
                adv(ndims, dims, subs);
            }
        }

        /* step 2: integrate */
        for (i = ; i < njoins; ++i)
        {
            unsigned int    index = joins[i];
            unsigned int    parent = r[index].parent;
            acc[parent] += acc[index];
        }

        /* step 3: save back to ellpises */
        for (i = ; i < nmer; ++i)
        {
            unsigned int idx = mer[i];
            ell[d + dof * i] = acc[idx];
        }
    } /* next dof */

      /* -----------------------------------------------------------------
      *                                           Compute central moments
      * -------------------------------------------------------------- */

    for (index = ; index < nmer; ++index)
    {
        float        *pt = ell + index * dof;
        unsigned int    idx = mer[index];
        float        area = (float)r[idx].area;

        for (d = ; d < dof; ++d)
        {
            pt[d] /= area;

            if (d >= ndims)
            {
                /* remove squared mean from moment to get variance */
                i = d - ndims;
                j = ;
                while (i > j)
                {
                    i -= j + ;
                    j++;
                }
                pt[d] -= pt[i] * pt[j];
            }
        }
    }

    /* save back */
    f->nell = nmer;
}

void drawEllipse(const float * region, int width, int height, int depth, unsigned char*  bits, const uint8_t * color)
{
    /* Centroid (mean) */
    const float    x = region[];
    const float    y = region[];

    /* Covariance matrix [a b; b c] */
    const float    a = region[];
    const float    b = region[];
    const float    c = region[];

    /* Eigenvalues of the covariance matrix */
    const float    d = a + c;
    const float    e = a - c;
    const float    f = sqrtf(4.0f * b * b + e * e);
    const float    e0 = (d + f) / 2.0f;       /* First eigenvalue */
    const float    e1 = (d - f) / 2.0f;       /* Second eigenvalue */

                                           /* Desired norm of the eigenvectors */
    const float    e0sq = sqrtf(e0);
    const float    e1sq = sqrtf(e1);

    /* Eigenvectors */
    float    v0x = e0sq;
    float    v0y = 0.0f;
    float    v1x = 0.0f;
    float    v1y = e1sq;

    if (b)
    {
        v0x = e0 - c;
        v0y = b;
        v1x = e1 - c;
        v1y = b;

        /* Normalize the eigenvectors */
        const float n0 = e0sq / sqrtf(v0x * v0x + v0y * v0y);
        v0x *= n0;
        v0y *= n0;

        const float n1 = e1sq / sqrtf(v1x * v1x + v1y * v1y);
        v1x *= n1;
        v1y *= n1;
    }

    for (float t = 0.0f; t < 2.0f * M_PI; t += 0.001f)
    {
        int    x2 = (int)(x + (cosf(t) * v0x + sinf(t) * v1x) * 2.0f + 0.5f);
        int    y2 = (int)(y + (cosf(t) * v0y + sinf(t) * v1y) * 2.0f + 0.5f);

        if ((x2 >= ) && (x2 < width) && (y2 >= ) && (y2 < height))
            for (int i = ; i < min(depth, ); ++i)
                bits[(y2 * width + x2) * depth + i] = color[i];
    }
}

/** @brief MSER driver entry point
**/
int
main(int argc, char **argv)
{
    /* algorithm parameters */
    float    delta = ;
    float    max_area = 0.5f;
    float    min_area = 0.0001f;
    float    max_variation = 0.5f;
    float    min_diversity = 0.33f;
    int    dark_on_bright = ;

    bool        err = false;
    char        err_msg[];
    int        exit_code = ;
    MserFilt    *filt = ;
    MserFilt    *filtinv = ;

    unsigned int const    *regions;
    unsigned int const    *regionsinv;
    float const        *frames;
    float const        *framesinv;
    enum { ndims =  };
    int    dims[ndims];
    int    nregions = , nregionsinv = , nframes = , nframesinv = ;
    int    i, dof;

    if (argc != )
    {
        fprintf
        (stderr,
            "Usage: %s input.jpg output.jpg\n",
            argv[]);
        return(-);
    }
    char    * inputfile = argv[];
    char    * outputfile = argv[];

    int        width;
    int        height;
    int        depth;
    unsigned char    * data = loadImage(inputfile, &width, &height, &depth);

    unsigned char *datainv = NULL;
    if (!data)
    {
        err = false;
        snprintf(err_msg, sizeof(err_msg),
            "Could not allocate enough memory.");
        goto done;
    }
    dims[] = width;
    dims[] = height;

    filt = mser_new(ndims, dims);
    filtinv = mser_new(ndims, dims);

    if (!filt || !filtinv)
    {
        snprintf(err_msg, sizeof(err_msg),
            "Could not create an MSER filter.");
        goto done;
    }

    if (delta >= )
        mser_set_delta(filt, (unsigned char)delta);
    if (max_area >= )
        mser_set_max_area(filt, max_area);
    if (min_area >= )
        mser_set_min_area(filt, min_area);
    if (max_variation >= )
        mser_set_max_variation(filt, max_variation);
    if (min_diversity >= )
        mser_set_min_diversity(filt, min_diversity);
    if (delta >= )
        mser_set_delta(filtinv, (unsigned char)delta);
    if (max_area >= )
        mser_set_max_area(filtinv, max_area);
    if (min_area >= )
        mser_set_min_area(filtinv, min_area);
    if (max_variation >= )
        mser_set_max_variation(filtinv, max_variation);
    if (min_diversity >= )
        mser_set_min_diversity(filtinv, min_diversity);

    printf("mser: parameters:\n");
    printf("mser:   delta         = %d\n", mser_get_delta(filt));
    printf("mser:   max_area      = %g\n", mser_get_max_area(filt));
    printf("mser:   min_area      = %g\n", mser_get_min_area(filt));
    printf("mser:   max_variation = %g\n", mser_get_max_variation(filt));
    printf("mser:   min_diversity = %g\n", mser_get_min_diversity(filt));

    if (dark_on_bright)
    {
        double startTime = now();
        mser_process(filt, (unsigned char *)data);
        double nProcessTime = calcElapsed(startTime, now());
        printf("Elapsed: %d ms \n ", (int)(nProcessTime * ));
        /* Save result  ----------------------------------------------- */
        nregions = mser_get_regions_num(filt);
        regions = mser_get_regions(filt);

        printf("nregions: %d \t", nregions); 

        /*
        * for (i = 0; i < nregions; ++i) {
        * printf(" %d \t", regions[i]);
        * }
        */
        mser_ell_fit(filt);

        nframes = mser_get_ell_num(filt);
        dof = mser_get_ell_dof(filt);

        printf("dof: %d \t", dof);
        printf("nframes: %d \t", nframes);
        /* Draw ellipses in the original image */
        const uint8_t colors[] = { , ,  };
        for (int x = ; x < ; ++x)
        {
            frames = mser_get_ell(filt);
            for (i = ; i < nframes; ++i)
            {
                drawEllipse(frames, width, height, depth, data, colors);
                frames += dof;
            }
        }
        saveJpeg(outputfile, width, height, depth, data);
    }
    else {
        /* allocate buffer */
        datainv = (unsigned char *)malloc(width * height * depth);
        for (i = ; i < width * height * depth; i++)
        {
            datainv[i] = ~data[i]; /* 255 - data[i] */
        }

        if (!datainv)
        {
            err = false;
            snprintf(err_msg, sizeof(err_msg),
                "Could not allocate enough memory.");
            goto done;
        }
        double startTime = now();
        mser_process(filtinv, (unsigned char *)datainv);
        double nProcessTime = calcElapsed(startTime, now());
        printf("Elapsed: %d ms \n ", (int)(nProcessTime * ));
        /* Save result  ----------------------------------------------- */
        nregionsinv = mser_get_regions_num(filtinv);
        regionsinv = mser_get_regions(filtinv);

        /*
        * for (i = 0; i < nregionsinv; ++i) {
        * printf("%d \t ", -regionsinv[i]);
        * }
        */

        mser_ell_fit(filtinv);

        nframesinv = mser_get_ell_num(filtinv);
        dof = mser_get_ell_dof(filtinv);

        const uint8_t colors[] = { , ,  };

        framesinv = mser_get_ell(filtinv);
        for (i = ; i < nframesinv; ++i)
        {
            drawEllipse(framesinv, width, height, depth, data, colors);
            framesinv += dof;
        }
        saveJpeg(outputfile, width, height, depth, data);
    }

    /* Next guy  ----------------------------------------------- */
done:
    /* release filter */
    if (filt)
    {
        mser_delete(filt);
        filt = ;
    }
    if (filtinv)
    {
        mser_delete(filtinv);
        filtinv = ;
    }

    /* release image data */
    if (data)
    {
        free(data);
        data = ;
    }
    if (datainv)
    {
        free(datainv);
        datainv = ;
    }

    /* if bad print error message */
    if (err)
    {
        fprintf
        (stderr,
            "mser: err: %s (%d)\n",
            err_msg,
            err);
        exit_code = ;
    }
    /* quit */
    return(exit_code);
}

算法有两种模式，白底黑字，白字黑底，可根据具体需求进行开关。

可参照《图片文档倾斜矫正算法 附完整c代码》中判断是否为文本图片的方式进行算法思路的改进。

效果图例：

以上，再一次抛砖引玉。

若有其他相关问题或者需求也可以邮件联系俺探讨。

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gaozhihan@vip.qq.com