Binarizer.java

/*
 * Copyright 2009 ZXing authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.zxing;

import com.google.zxing.common.BitArray;
import com.google.zxing.common.BitMatrix;

/**
 * This class hierarchy provides a set of methods to convert luminance data to 1
 * bit data. It allows the algorithm to vary polymorphically, for example
 * allowing a very expensive thresholding technique for servers and a fast one
 * for mobile. It also permits the implementation to vary, e.g. a JNI version
 * for Android and a Java fallback version for other platforms.
 * 
 * @author dswitkin@google.com (Daniel Switkin)
 */
public abstract class Binarizer {

	private final LuminanceSource source;

	protected Binarizer(LuminanceSource source) {
		this.source = source;
	}

	public final LuminanceSource getLuminanceSource() {
		return source;
	}

	/**
	 * Converts one row of luminance data to 1 bit data. May actually do the
	 * conversion, or return cached data. Callers should assume this method is
	 * expensive and call it as seldom as possible. This method is intended for
	 * decoding 1D barcodes and may choose to apply sharpening. For callers
	 * which only examine one row of pixels at a time, the same BitArray should
	 * be reused and passed in with each call for performance. However it is
	 * legal to keep more than one row at a time if needed.
	 * 
	 * @param y
	 *            The row to fetch, which must be in [0, bitmap height)
	 * @param row
	 *            An optional preallocated array. If null or too small, it will
	 *            be ignored. If used, the Binarizer will call BitArray.clear().
	 *            Always use the returned object.
	 * @return The array of bits for this row (true means black).
	 * @throws NotFoundException
	 *             if row can't be binarized
	 */
	public abstract BitArray getBlackRow(int y, BitArray row)
			throws NotFoundException;

	/**
	 * Converts a 2D array of luminance data to 1 bit data. As above, assume
	 * this method is expensive and do not call it repeatedly. This method is
	 * intended for decoding 2D barcodes and may or may not apply sharpening.
	 * Therefore, a row from this matrix may not be identical to one fetched
	 * using getBlackRow(), so don't mix and match between them.
	 * 
	 * @return The 2D array of bits for the image (true means black).
	 * @throws NotFoundException
	 *             if image can't be binarized to make a matrix
	 */
	public abstract BitMatrix getBlackMatrix() throws NotFoundException;

	/**
	 * Creates a new object with the same type as this Binarizer implementation,
	 * but with pristine state. This is needed because Binarizer implementations
	 * may be stateful, e.g. keeping a cache of 1 bit data. See Effective Java
	 * for why we can't use Java's clone() method.
	 * 
	 * @param source
	 *            The LuminanceSource this Binarizer will operate on.
	 * @return A new concrete Binarizer implementation object.
	 */
	public abstract Binarizer createBinarizer(LuminanceSource source);

	public final int getWidth() {
		return source.getWidth();
	}

	public final int getHeight() {
		return source.getHeight();
	}

}