LIBDMTX(3)                                                          LIBDMTX(3)

       libdmtx - Data Matrix Encoding & Decoding Library 0.7.2

       #include <dmtx.h>

       cc file.c -ldmtx

       libdmtx  is  a software library that enables programs to read and write
       Data Matrix barcodes of the modern ECC200  variety.  The  library  runs
       natively  on  several  platforms,  and can be accessed by multiple lan-
       guages using  the  libdmtx  language  wrappers.  The  utility  programs
       dmtxread  and  dmtxwrite  provide a command line interface for libdmtx,
       and serve as a good reference for developers writing their own libdmtx-
       enabled programs.

       Data  Matrix  barcodes  store  data  as a pattern of ON and OFF modules
       (often black on white) in a grid pattern that resembles a checkerboard.
       Like  other  2D  symbologies,  Data  Matrix  barcodes have a large data
       capacity compared to their traditional 1D cousins, and employ sophisti-
       cated  error  correction techniques. Data Matrix barcodes can be square
       or rectangle in shape, and offer several encodation schemes  for  opti-
       mized storage of text and/or binary data. The Data Matrix symbology was
       invented and released into the public domain by RVSI Acuity CiMatrix.

ENCODING - Generating Data Matrix Barcodes
       C/C++ programs can generate a barcode with just a few  basic  calls  to

       1. Call dmtxEncodeCreate()

       Creates  a  new  DmtxEncode structure and initializes the encoding pro-
       cess. This function must be called  before  using  the  other  encoding

       2. Call dmtxEncodeSetProp() [optional]

       Allows  you  to  control  specific aspects of the encoding behavior. If
       this function is not called, libdmtx will use the defaults set by dmtx-
       EncodeCreate()  above. The complementary function, dmtxEncodeGetProp(),
       allows you to detect the current settings.

       3. Call either dmtxEncodeDataMatrix() or dmtxEncodeDataMosaic()

       Call one of these functions to generate an image of the desired barcode
       type.  Your program is responsible for dispatching the resulting output
       to its destination, whether that means displaying it on a screen, writ-
       ing an image file, copying it elsewhere, etc...

       4. Call dmtxEncodeDestroy()

       Releases memory allocated during the encoding process.

DECODING - Reading Data Matrix Barcodes
       Barcode  reading  takes  more  steps  than  barcode  generation, mainly
       because libdmtx must find a barcode region before  it  can  decode  the
       message.  However,  this too is a relatively simple process that uses 4
       main structures:

       DmtxImage holds image properties and a pointer to pixel  data  held  by
       the calling program.

       DmtxDecode  holds  values  for controlling decode behavior and tracking
       scan progress. When scanning  a  new  image,  calling  programs  should
       always create a new DmtxDecode structure instead of reusing an old one.

       DmtxRegion defines a 4-sided region in pixel coordinates.  Regions  may
       be found in almost any orientation, and their corners won't necessarily
       form right angles. libdmtx uses this structure to store the location of
       potential barcodes, which are then returned to the calling program one-

       DmtxMessage holds the decoded message after being  extracted  from  the
       barcode  region. A successfully decoded region will produce exactly one

       Use the following functions to find and decode Data Matrix barcodes:

       1. Call dmtxImageCreate()

       Creates and initializes a new DmtxImage structure using pixel data pro-
       vided  by  the calling application. Parameters include a pointer to the
       existing pixel array, image width, height, and the pixel  packing  for-

       2. Call dmtxImageSetProp() [optional]

       Sets  image  properties  to control the pixel mapping logic. These set-
       tings allow libdmtx to understand many native in-memory image  layouts,
       thus  preventing  the  extra work of transforming and copying data to a
       one-size-fits-all format. A dmtxDecodeGetProp() function is also avail-
       able for detecting the current image properties.

       3. Call dmtxDecodeCreate()

       Creates  and  initializes a new DmtxDecode struct, which designates the
       image to be scanned and initializes the scan grid pattern.  This  func-
       tion must be called before any other scanning functions.

       4. Call dmtxDecodeSetProp() [optional]

       Sets  internal  properties  to  control decoding behavior. This feature
       allows you to optimize performance and accuracy for specific image con-
       ditions. A dmtxDecodeGetProp() function is also available.

       5. Call dmtxRegionFindNext()

       Searches  every  pixel location in a grid pattern looking for potential
       barcode regions. A DmtxRegion is returned whenever a potential  barcode
       region  is found, or if the final pixel location has been scanned. Sub-
       sequent calls to this function will resume the search where the  previ-
       ous call left off.

       6. Call either dmtxDecodeMatrixRegion() or dmtxDecodeMosaicRegion()

       Extracts  raw  data  from the barcode region and decodes the underlying

       7. Call dmtxMessageDestroy()

       Releases memory held by a DmtxMessage struct. The  complementary  func-
       tion,  dmtxMessageCreate(),  is  automatically  called by dmtxDecodeMa-
       trixRegion() and therefore is not normally used by the calling program.

       8. Call dmtxRegionDestroy()

       Releases  memory  held  by a DmtxRegion struct. The complementary func-
       tion, dmtxRegionCreate(), is automatically  called  by  dmtxRegionFind-
       Next()  (actually  dmtxRegionScanPixel()) and therefore is not normally
       used by the calling program.

       9. Call dmtxDecodeDestroy()

       Releases memory held by a DmtxDecode struct. This is the  complementary
       function to dmtxDecodeCreate().

       10. Call dmtxImageDestroy()

       Releases  memory  held by a DmtxImage struct, excluding the pixel array
       passed to dmtxImageCreate(). The calling  program  is  responsible  for
       releasing the pixel array memory, if required.

       This example program (available as simple_test.c in the source package)
       demonstrates libdmtx functionality in  both  directions:  encoding  and
       decoding.  It  creates  a Data Matrix barcode in memory, reads it back,
       and prints the decoded message. The final output message  should  match
       the original input string.

         #include <stdlib.h>
         #include <stdio.h>
         #include <string.h>
         #include <assert.h>
         #include <dmtx.h>

         main(int argc, char *argv[])
            size_t          width, height, bytesPerPixel;
            unsigned char   str[] = "30Q324343430794<OQQ";
            unsigned char  *pxl;
            DmtxEncode     *enc;
            DmtxImage      *img;
            DmtxDecode     *dec;
            DmtxRegion     *reg;
            DmtxMessage    *msg;

            fprintf(stdout, "input:  \"%s\"\n", str);

            /* 1) ENCODE a new Data Matrix barcode image (in memory only) */

            enc = dmtxEncodeCreate();
            assert(enc != NULL);
            dmtxEncodeDataMatrix(enc, strlen(str), str);

            /* 2) COPY the new image data before releasing encoding memory */

            width = dmtxImageGetProp(enc->image, DmtxPropWidth);
            height = dmtxImageGetProp(enc->image, DmtxPropHeight);
            bytesPerPixel = dmtxImageGetProp(enc->image, DmtxPropBytesPerPixel);

            pxl = (unsigned char *)malloc(width * height * bytesPerPixel);
            assert(pxl != NULL);
            memcpy(pxl, enc->image->pxl, width * height * bytesPerPixel);


            /* 3) DECODE the Data Matrix barcode from the copied image */

            img = dmtxImageCreate(pxl, width, height, DmtxPack24bppRGB);
            assert(img != NULL);

            dec = dmtxDecodeCreate(img, 1);
            assert(dec != NULL);

            reg = dmtxRegionFindNext(dec, NULL);
            if(reg != NULL) {
               msg = dmtxDecodeMatrixRegion(dec, reg, DmtxUndefined);
               if(msg != NULL) {
                  fputs("output: \"", stdout);
                  fwrite(msg->output, sizeof(unsigned char), msg->outputIdx, stdout);
                  fputs("\"\n", stdout);



       dmtxread(1), dmtxwrite(1), dmtxquery(1)

       ISO/IEC 16022:2000

       ANSI/AIM BC11 ISS

       Email bug reports to

       Copyright (C) 2008, 2009 Mike Laughton

                               September 4, 2009                    LIBDMTX(3)