ZBar source code analysis - img_ scanner. c | [email protected]

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One 、ZBar workflow

Through analysis ZBar Project structure , You can see ZBar The workflow of is roughly divided into 4 A step ：

（ One ） Read in images and configure parameters ;

（ Two ） Scan the read image and analyze its light and dark width flow according to the gradient change （ According to the light and dark width flow, the barcode type read into the image can be obtained , Such as ： QR code ,code93,code128 etc. ）;

（ 3、 ... and ） Analyze the pixels and their characteristics of the read image ;

（ Four ） Find the barcode format information and decode , Finally, output the recovered codeword .

Two 、Image Scanner

Image Scanner, As the name suggests, it is a functional module to scan the read image . Of this secondary analysis scanner.c It is one of the cores of this functional module . 

ZBar Realization Image Scanner The core of is mainly composed of img_scanner.c and scanner.c Two documents .

among ,img_scanner.c The core function in is zbar_scan_image(), and scanner.c The core function in is zbar_scan_y(). After simple analysis, we get ,zbar_scan_image Mainly responsible for ZBar Scanning the read in image , The function is mainly based on the set scanning density (density) Control pixel reading ( Press Z Font reading , This is also ZBar The origin of the name ),scanner.c In file zbar_scan_y() To complete the filtering , threshold , Determine the edge , Convert to width flow .

zbar_scan_image() The implementation of needs the help of zbar_scan_y() The scanning image forms the result of width flow .

3、 ... and 、img_scanner.c

This source code analysis mainly focuses on img_scanner.c Document analysis （ Main analysis zbar_scan_image() function ）.

zbar_image_scanner_create() establish （ install ） Picture scanner Image Scanner It is applied to decoding and recognition of various bar codes .

// Function implementation of creating image scanner 
zbar_image_scanner_t *zbar_image_scanner_create ()
{
    zbar_image_scanner_t *iscn = calloc(1, sizeof(zbar_image_scanner_t));
// If the creation fails , return NULL
    if(!iscn)
        return(NULL);
// Initialize the picture scanner （ Initialize the decoder and scanner in the picture scanner ）
    iscn->dcode = zbar_decoder_create();
    iscn->scn = zbar_scanner_create(iscn->dcode);
// If decoder or scanner initialization fails , return NULL
    if(!iscn->dcode || !iscn->scn) {
        zbar_image_scanner_destroy(iscn);
        return(NULL);
    }
// Apply the picture scanner to the decoder 
    zbar_decoder_set_userdata(iscn->dcode, iscn);
    zbar_decoder_set_handler(iscn->dcode, symbol_handler);

#ifdef ENABLE_QRCODE
    iscn->qr = _zbar_qr_create();
#endif
// Apply the picture scanner to the recognition of various bar codes 
    CFG(iscn, ZBAR_CFG_X_DENSITY) = 1;
    CFG(iscn, ZBAR_CFG_Y_DENSITY) = 1;
    zbar_image_scanner_set_config(iscn, 0, ZBAR_CFG_POSITION, 1);
    zbar_image_scanner_set_config(iscn, 0, ZBAR_CFG_UNCERTAINTY, 2);
    zbar_image_scanner_set_config(iscn, ZBAR_QRCODE, ZBAR_CFG_UNCERTAINTY, 0);
    zbar_image_scanner_set_config(iscn, ZBAR_CODE128, ZBAR_CFG_UNCERTAINTY, 0);
    zbar_image_scanner_set_config(iscn, ZBAR_CODE93, ZBAR_CFG_UNCERTAINTY, 0);
    zbar_image_scanner_set_config(iscn, ZBAR_CODE39, ZBAR_CFG_UNCERTAINTY, 0);
    zbar_image_scanner_set_config(iscn, ZBAR_CODABAR, ZBAR_CFG_UNCERTAINTY, 1);
    zbar_image_scanner_set_config(iscn, ZBAR_COMPOSITE, ZBAR_CFG_UNCERTAINTY, 0);
    return(iscn);
}

  When you need to uninstall Image Scanner when , Not directly free(img_scanner) Free up memory , This will directly lead to ZBar Scanner zbar_scanner、ZBar decoder zbar_decoder And all kinds of bar code recognition applications have null pointer exceptions . So we need to judge Image Scanner Usage in various components and Applications , If you are using , You need to remove Image Scanner Application , Finally, the memory can be directly released .

// Unloading of image scanner 
void zbar_image_scanner_destroy (zbar_image_scanner_t *iscn)
{
    int i;
    dump_stats(iscn);
// Determine the status of the image scanner , If it is in the application state , You cannot uninstall 
    if(iscn->syms) {
        if(iscn->syms->refcnt)
            zbar_symbol_set_ref(iscn->syms, -1);
        else
            _zbar_symbol_set_free(iscn->syms);
        iscn->syms = NULL;
    }
// Determine whether the image scanner is applied to ZBar Scanner , If it is , From ZBar Unload on the scanner 
    if(iscn->scn)
        zbar_scanner_destroy(iscn->scn);
    iscn->scn = NULL;
 Determine whether the image scanner is applied to ZBar decoder , If it is , From ZBar Uninstall on the decoder 
    if(iscn->dcode)
        zbar_decoder_destroy(iscn->dcode);
    iscn->dcode = NULL;
// Unload the picture scanner from the recognition application of various bar codes 
    for(i = 0; i < RECYCLE_BUCKETS; i++) {
        zbar_symbol_t *sym, *next;
        for(sym = iscn->recycle[i].head; sym; sym = next) {
            next = sym->next;
            _zbar_symbol_free(sym);
        }
    }
#ifdef ENABLE_QRCODE
    if(iscn->qr) {
        _zbar_qr_destroy(iscn->qr);
        iscn->qr = NULL;
    }
#endif
    free(iscn);
}

The following is true. zbar_scan_image() Analysis of some code fragments ：

zbar_scan_image() Mainly achieved Z Font scanning image density , The core idea is through scanning density (density) To control pixel reading .

The function is divided into two parts: scanning the image horizontally and vertically , The implementation logic is not much different , The code of the longitudinal scanning part is given below .

density = CFG(iscn, ZBAR_CFG_Y_DENSITY);
    if(density > 0) {
        const uint8_t *p = data;
        int x = 0, y = 0;

        int border = (((img->crop_h - 1) % density) + 1) / 2;
        if(border > img->crop_h / 2)
            border = img->crop_h / 2;
        border += img->crop_y;
        assert(border <= h);
        svg_group_start("scanner", 0, 1, 1, 0, 0);
        iscn->dy = 0;

        movedelta(img->crop_x, border);
        iscn->v = y;

        while(y < cy1) {
            int cx0 = img->crop_x;;
            zprintf(128, "img_x+: %04d,%04d @%p\n", x, y, p);
            svg_path_start("vedge", 1. / 32, 0, y + 0.5);
            iscn->dx = iscn->du = 1;
            iscn->umin = cx0;
            while(x < cx1) {
                uint8_t d = *p;
                movedelta(1, 0);
                zbar_scan_y(scn, d);
            }
            ASSERT_POS;
            quiet_border(iscn);
            svg_path_end();

            movedelta(-1, density);
            iscn->v = y;
            if(y >= cy1)
                break;

            zprintf(128, "img_x-: %04d,%04d @%p\n", x, y, p);
            svg_path_start("vedge", -1. / 32, w, y + 0.5);
            iscn->dx = iscn->du = -1;
            iscn->umin = cx1;
            while(x >= cx0) {
                uint8_t d = *p;
                movedelta(-1, 0);
                zbar_scan_y(scn, d);
            }
            ASSERT_POS;
            quiet_border(iscn);
            svg_path_end();

            movedelta(1, density);
            iscn->v = y;
        }
        svg_group_end();
    }
    iscn->dx = 0;

This part of the code mainly realizes the longitudinal scanning image density , Because the calling function relationship is complex , If you only look at the coordinates , It can be simplified to the following code ：

// First judge whether there is a setting y density 
if(ydensity > 0)
 {
     while(y < h)  
//y from 0 With ydensity Increase to h
 {
   while(x < w) 
//x First from 0 Increase to w, Re decrement back 0
   {
      x += 1;
      zbar_scan_y();
   }
   x = w - 1;
   y = y + ydensity 
//y from 0 With ydensity Increase to h
   if(y >= h)
     break;
   while(x >= 0)
//  x Begin to decline 
   {
      x -= 1;
      zbar_scan_y();
   }
   x = 0 + 1;
   y = y + ydensity;
 }
// Then judge x Directional scanning density , Empathy Z Glyph scanning 
}

 w = img->width;
 h = img->height;

In the above code w Represents the width of the image ,h Represents the height of the image , The function is called repeatedly during the loop zbar_scan_y() To complete the filtering , threshold , Determine the edge , Convert to width flow .

Draw according to the code , You can roughly get ZBar The order of scanning image pixels is roughly as follows ：

  The above is the code analysis report , If there is a mistake , Please correct me. .