Scan multiple barcodes with zxing.net

Question

My aim is to detect multiple datamatrices on a larger image like this (the four big):

Based on several code samples, I made a small test program:

Bitmap image = getImage();

DataMatrixReader reader = new DataMatrixReader();
GenericMultipleBarcodeReader genericReader = new genericMultipleBarcodeReader(reader);
Dictionary<DecodeHintType, object> hints = new Dictionary<DecodeHintType,object>();
hints.Add(DecodeHintType.TRY_HARDER, true);

BitmapLuminanceSource source = new BitmapLuminanceSource(image);
HybridBinarizer binarizer = new HybridBinarizer(source);
BinaryBitmap binaryBitmap = new BinaryBitmap(binarizer);
Result[] results = genericReader.decodeMultiple(binaryBitmap,hints);

show(results);

It could'nt detect any code on the large image.

But it can detect the code, when its cropped like that:

After that I merged two generated data matrices, and it failed too:

Last I ran two more test with slightly cropped images, both failed:

So it seems this library is not robust at all, or maybe I use it wrong.

Any idea how to improve my results? (including other libraries and preprocessing)

Answer 1

It can't be said that the library is not robust but there are two key factors affecting you here:

• Zxing's data-matrix detection algorithm assumes that the barcode is centered. Or more precisely, that the center of the image is inside the data-matrix.
• Zxing's multiple reader specially fails when barcodes are grid-aligned.

My recommendation is to implement your own MultipleBarcodeReader taking into account what I've mentioned.

A naive approach could be to take sample images centered over a grid of points spaced so every data-matrix (no matter its position within the image) contain at least one of the points inside. You just have to make sure to exclude duplicated codes.