目标检测数据库 PASCAL 格式的 Ground Truth 的解析函数

最近在做一个目标检测算法，训练时用到了 bootstrap 策略，于是我将 PASCAL 的 Ground Truth 格式的读取函数从 Matlab 改写为 C++。PASCAL 的标注格式为：

# PASCAL Annotation Version 1.00

Image filename : "对应图片路径"
Image size (X x Y x C) : 宽 x 高 x 3
Database : "数据库名称"
Objects with ground truth : 1 { "PASperson" }

# Note that there might be other objects in the image
# for which ground truth data has not been provided.

# Top left pixel co-ordinates : (0, 0)

# Details for object 1 ("PASperson")
# Center point -- not available in other PASCAL databases -- refers
# to person head center
Original label for object 1 "PASperson" : "UprightPerson"
Center point on object 1 "PASperson" (X, Y) : (257, 187)
Bounding box for object 1 "PASperson" (Xmin, Ymin) - (Xmax, Ymax) : (195, 154) - (297, 468)

 我写的函数如下：

#include "stdio.h"

#include "string.h"

#include "stdlib.h"



// object bounding rect

struct GtRect {

    int x_min; int y_min;

    int x_max; int y_max; 

};



// ground truth of one image

struct GtRecord {

    char* image_name;

    GtRect* objs;

    int obj_num; int height;

    int width; int channels;

};



// return true if c is in char set s

int _is_chars(char c, const char* s, int n)

{

    for (int i = 0; i != n; ++i) {

        if (s[i] == c) {

            return 1;

        }

    }

    return 0;

}



void _trim_l(char* inout, const char* s)

{

    int len = strlen(inout);

    int s_len = strlen(s);

    int i = 0;

    for (;i != len; ++i) {

        if (!_is_chars(inout[i], s, s_len)) {

            break;

        }

    }

    int d = i;

    int new_len = len - d;

    for (i = 0; i != new_len; ++i) {

        inout[i] = inout[i + d];

    }

    inout[new_len] = '\0';

}



void _trim_r(char* inout, const char* s)

{

    int len = strlen(inout);

    int s_len = strlen(s);

    int i = len - 1;

    for (;i != -1; --i) {

        if (!_is_chars(inout[i], s, s_len)) {

            break;

        }

    }

    inout[i + 1] = '\0';

}



inline void _trim_lr(char* inout, const char* s)

{

    _trim_l(inout, s);

    _trim_r(inout, s);

}



// read ground truth (pascal format)

//************************************

// Name:  gt_pascal_read

// Returns:   GtRecord

// const char * path    :    groundtruth file path

//************************************

GtRecord gt_pascal_read(const char* path)

{

    GtRecord ret = {0, 0, 0, 0, 0, 0};

    FILE* f;

    fopen_s(&f, path, "r");

    int obj_num = 0;

    int len = 0;

    GtRect rct;

    while (fgets(BUF1, 5000, f) != 0) {

        int match_type = _match_attr(BUF1);

        switch (match_type) {

        case 0:

            // read image filename

            sscanf_s(BUF1, _GT_ATTR[0], BUF2, 500);

            _trim_lr(BUF2, "\n\" ");

            len = strlen(BUF2);

            ret.image_name = (char*)malloc(len + 1);

            memcpy(ret.image_name, BUF2, len + 1);

            break;

        case 1:

            // read image size, channel

            sscanf_s(BUF1, _GT_ATTR[1], &ret.width, &ret.height,

                &ret.channels);

            break;

        case 2:

            // ignore database name

            break;

        case 3:

            sscanf_s(BUF1, _GT_ATTR[3], &rct.x_min,

                &rct.y_min, &rct.x_max, &rct.y_max);

            OBJ_BUF[obj_num++] = rct;

            break;

        case 4:

            // ignore polygon

        case 5:

            // ignore pixel map

        case 6:    

            // ignore label    

            break;

        }

    }

    fclose(f);

    ret.obj_num = obj_num;

    if (obj_num > 0) {

        ret.objs = (GtRect*)malloc(sizeof(GtRect) * obj_num);

        memcpy(ret.objs, OBJ_BUF, obj_num * sizeof(GtRect));

    }

    return ret;

}



// release pascal ground truth

//************************************

// Name:  gt_pascal_release

// Returns:   void

// GtRecord * r

//************************************

void gt_pascal_release(GtRecord* r)

{

    free(r->image_name);

    free(r->objs);

    r->image_name = 0;

    r->objs = 0;

    r->width = 0;

    r->height = 0;

    r->channels = 0;

    r->obj_num = 0;

}

gt_pascal_read 函数忽略了 groundtruth 文件中的一些属性，例如数据库名称等，如果要加回，可以在函数的几个空的 case 中添加即可。PASCAL 官方提供了几个有用的 Matlab 脚本用于读取和生成这样的 groundtruth 文件，在算法开发的过程中要多利用这样的工具。