Calculates the final BitMatrix once for all requests. This could be called once from the constructor instead, but there are some advantages to doing it lazily, such as making profiling easier, and not doing heavy lifting when callers don't expect it.
Calculates a single black point for each block of pixels and saves it away. See the following thread for a discussion of this algorithm: http://groups.google.com/group/zxing/browse_thread/thread/d06efa2c35a7ddc0
For each block in the image, calculate the average black point using a 5x5 grid of the blocks around it. Also handles the corner cases (fractional blocks are computed based on the last pixels in the row/column which are also used in the previous block).
Applies a single threshold to a block of pixels.
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This class implements a local thresholding algorithm, which while slower than the GlobalHistogramBinarizer, is fairly efficient for what it does. It is designed for high frequency images of barcodes with black data on white backgrounds. For this application, it does a much better job than a global blackpoint with severe shadows and gradients. However it tends to produce artifacts on lower frequency images and is therefore not a good general purpose binarizer for uses outside ZXing.
This class extends GlobalHistogramBinarizer, using the older histogram approach for 1D readers, and the newer local approach for 2D readers. 1D decoding using a per-row histogram is already inherently local, and only fails for horizontal gradients. We can revisit that problem later, but for now it was not a win to use local blocks for 1D.
This Binarizer is the default for the unit tests and the recommended class for library users.
dswitkin@google.com (Daniel Switkin)