L_BarCodeReadExt

Summary

Searches for barcodes within the specified area with callback functionality.

Syntax

L_LTBAR_API L_INT L_BarCodeReadExt(pBitmap, prcSearch, ulSearchType, nUnits, ulFlags, nMultipleMaxCount, pBarCode1D, pBarCodePDF, pBarCodeColor, ppBarCodeData, pfnCallback, pUserData, uStructSize)

Parameters

pBITMAPHANDLE pBitmap

Pointer to the bitmap handle referencing the bitmap that holds the image data.

RECT * prcSearch

Pointer to the rectangle that contains the search area for the barcodes. Pass NULL to search the whole image. If this parameter is NULL and the image does not have a region, the entire image will be searched. If this parameter is NULL and the image does have a region, only the region will be searched.

L_UINT32 ulSearchType

Type of barcode for which to search. You can combine values when appropriate among the same group values, by using a bitwise OR ( | ). Possible values are:

Linear Barcode:

Patch Code Barcodes:

Postal barcodes:

4 State barcode symbols:

GS1 Databar (formerly RSS14) Stacked barcode symbols:

PDF Barcodes:

MicroPDF417 Barcodes:

QR Barcodes:

Data Matrix Barcode:

Aztec Barcode:

Maxi Barcode:

MicroQR Barcode:

Other barcode symbol:

L_INT nUnits

Unit of measure. Possible values are:

L_UINT32 ulFlags

Processing options. You can combine values when appropriate, by using a bitwise OR ( | ). The following values are used only when you want to search for linear barcodes. Pass 0 to get the default. Possible values are:

L_INT nMultipleMaxCount

Specifies the maximum number of barcodes to search. Pass 0 to read all barcodes in a specified search area.

pBARCODE1D pBarCode1D

Pointer to the BARCODE1D structure. Pass NULL to use the default structure or if you don't want to search for linear barcodes.

pBARCODEREADPDF pBarCodePDF

Pointer to the BARCODEREADPDF structure. Pass NULL to use the default structure or if you don't want to search for PDF barcodes.

pBARCODECOLOR pBarCodeColor

Pointer to the BARCODECOLOR structure. Pass NULL to search for barcode using the default colors.

pBARCODEDATA * ppBarCodeData

Address of the pointer to the BARCODEDATA structure, the function will automatically allocate an array of BARCODEDATA structures using the total number of barcodes found.

BARCODEREADCALLBACK pfnCallback

Optional callback function to be called when a barcode symbolgoy is decoded correctly. If you do not provide callback function, use NULL as the value of this parameter. If you do provide callback function, use the function pointer as the value of this parameter. The callback function must adhere to the function prototype described in BARCODEREADCALLBACK Function.

L_VOID * pUserData

Void pointer that you can use to pass one or more additional parameters that the help callback function needs. To use this feature, assign a value to a variable or create a structure that contains as many fields as you need. Then, in this parameter, pass the address of the variable or structure, casting it to L_VOID *. The callback function, which receives the address in its own pUserData parameter, can cast it to a pointer of the appropriate data type to access your variable or structure. If the additional parameters are not needed, you can pass NULL in this parameter.

L_UINT uStructSize

Size of BARCODEDATA structure in bytes. Use the sizeof operator to calculate this value.

Returns

Comments

This function supports all bitmaps currently supported by LEADTOOLS.

Use this function to recognize barcode data.

NOTE: RSS14 has been renamed as GS1 Databar. All references to RSS 14 now refer to GS1 Databar.

To determine if a barcode element is duplicated or not, use L_BarCodeIsDuplicated function. If the barcode is duplicated, you can get it using L_BarCodeGetDuplicated and to get the next duplicated barcode use L_BarCodeGetNextDuplicated.

If you know the index of a duplicated barcode, you can get the first duplicate of that barcode using L_BarCodeGetFirstDuplicated.

Since the function allocates storage to hold a Barcode array, you must free this storage by calling L_BarCodeFree.

When the BARCODE_USECOLORS flag is set this function will use the pBarCodeColor parameter. Otherwise, the function will ignore it and use the default colors of black for bars and white for spaces.

Using colors does not apply for 1-bit per pixel images.

The BARCODE_USECOLORS is used with all barcode kinds.

The BARCODE_RETURNCHECK flag is used only when reading linear barcodes.

The smallest Data Matrix symbol size is 40 pixels by 40 pixels. It can be read using BARCODE_DM_READ_SMALL since this enables the reading of Data Matrix symbols that are between 20 to 40 pixels in size.

The Linear barcodes are not supported in UNICODE.

When reading barcodes from poor quality images, use BARCODE_APPLY_PREPROCESSING to enable image segmentation and advanced image preprocessing during barcode recognition.

When reading 2D barcodes, LEADTOOLS can perform internal auto preprocessing using BARCODE_DOUBLE_PASS on the image and try again if the engine cannot detect the barcode required. But this may take extra processing which will increase the barcode detection time.  Hence, it is not recommended to always have it enabled except in certain situations:

• The application is reading barcodes of this type exclusively. For example, a dedicated PDF417 reader. Here, always reading the barcode is more important than recognition speed.

• The application uses barcode detection on a server. In this case, the time spent on the actual barcode detection is most probably less than the time required to send the image to the server and get the results back due to network latency. Thus, it makes sense to turn this feature on in this situation.

• The images provided have a small resolution (DPI) or are known to come from a source that does not always provide clean images. For example, a Fax machine or a Scanner. Enabling double pass here ensures that you can read the barcodes regardless of the quality of the input image.

The LEADTOOLS Barcode Demo leaves the option disabled by default.

When calling the L_BarCodeRead function with the BARCODE_RETURN_FOUR_POINTS flag set, the BARCODEDATA.rcBarLocation member will be updated with the coordinates of the four corners of the barcode rather than the coordinates of the bounding rectangle. These coordinates are encoded values and must be decoded before they can be used. The following example shows how to decode the four-point corner values:

POINT p1, p2, p3, p4; 
int nStartX = BarCodeData.rcBarLocation.left; 
int nStartY = BarCodeData.rcBarLocation.top; 
int nWidth = BarCodeData.rcBarLocation.right - nStartX; 
int nHeight = BarCodeData.rcBarLocation.bottom - nStartY; 
p1.x = (nStartX & 0xffff); 
p1.y = (nStartX >> 16); 
p2.x = (nStartY & 0xffff); 
p2.y = (nStartY >> 16); 
p3.x = (nWidth & 0xffff); 
p3.y = (nWidth >> 16); 
p4.x = (nHeight & 0xffff); 
p4.y = (nHeight >> 16); 

Reading Linear Barcodes (1D)

A barcode is composed of start mark, data, and end mark. Reading barcodes from left to right (passing BARCODE_DIR_LEFT_TO_RIGHT value to the nDirection member) or from right to left (passing BARCODE_DIR_RIGHT_TO_LEFT value to the nDirection member) will produce the same result in most cases, because the barcode reader engine recognizes the start and end marks, and handles the data accordingly.

For example, if BARCODE_DIR_LEFT_TO_RIGHT is passed and the user reads barcodes from left to right (the barcode is not rotated), the engine will recognize the start mark first, then the data, and finally the end mark.

But if the user reads barcodes from right to left (the barcode is rotated 180 degrees), the engine will first recognize the end mark, then read the (reverse-order) data, and then recognize the start mark. In this case, the engine will flip the data to normal (start/data/end) order.

Sample for BARCODE_RETURN_FOUR_POINTS

pBARCODEDATA barData; 
int nStartX, nStartY, nWidth, nHeight; 
POINT p1, p2, p3, p4; 
// Call L_BarCodeRead(&); 
nStartX = barData[0].rcBarLocation.left; 
nStartY = barData[0].rcBarLocation.top; 
nWidth = barData[0].rcBarLocation.right - nStartX; 
nHeight = barData[0].rcBarLocation.bottom - nStartY; 
p1.x = (nStartX & 0xffff); 
p1.y = (nStartX >> 16); 
p2.x = (nStartY & 0xffff); 
p2.y = (nStartY >> 16); 
p3.x = (nWidth & 0xffff); 
p3.y = (nWidth >> 16); 
p4.x = (nHeight & 0xffff); 
p4.y = (nHeight >> 16); 

For a table containing information useful when writing 1D barcode data, refer to Writing Linear 1D Barcodes.

QR stores up to 2335 ASCII characters in one barcode symbol.

DataMatrix stores up to 2218 ASCII characters in one barcode symbol.

PDF417 stores up to 1,850 ASCII characters in one barcode symbol.

MicroPDF stores up to 366 ASCII characters in one barcode symbol.

Required DLLs and Libraries

• LTBAR
• For a listing of the exact DLLs and Libraries needed, based on the toolkit version, refer to Files To Be Included With Your Application

Platforms

Win32, x64, Linux.

See Also

Functions

• L_BarCodeFree
• L_BarCodeIsDuplicated
• L_BarCodeGetDuplicated
• L_BarCodeGetNextDuplicated
• L_BarCodeVersionInfo
• L_BarCodeGetFirstDuplicated
• L_BarCodeWrite

Topics

• Programming with LEADTOOLS Barcode
• BarCode C API Function Groups