2 * Copyright 2007 Google Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 package com.google.zxing.client.j2se;
19 import com.google.zxing.MonochromeBitmapSource;
20 import com.google.zxing.BlackPointEstimationMethod;
21 import com.google.zxing.common.BitArray;
22 import com.google.zxing.common.BlackPointEstimator;
24 import java.awt.image.BufferedImage;
27 * <p>An implementation based upon {@link BufferedImage}. This provides access to the
28 * underlying image as if it were a monochrome image. Behind the scenes, it is evaluating
29 * the luminance of the underlying image by retrieving its pixels' RGB values.</p>
31 * @author srowen@google.com (Sean Owen), Daniel Switkin (dswitkin@google.com)
33 public final class BufferedImageMonochromeBitmapSource implements MonochromeBitmapSource {
35 private final BufferedImage image;
36 private int blackPoint;
37 private BlackPointEstimationMethod lastMethod;
38 private int lastArgument;
40 private static final int LUMINANCE_BITS = 5;
41 private static final int LUMINANCE_SHIFT = 8 - LUMINANCE_BITS;
42 private static final int LUMINANCE_BUCKETS = 1 << LUMINANCE_BITS;
44 public BufferedImageMonochromeBitmapSource(BufferedImage image) {
51 public boolean isBlack(int x, int y) {
52 return computeRGBLuminance(image.getRGB(x, y)) < blackPoint;
55 public BitArray getBlackRow(int y, BitArray row, int startX, int getWidth) {
57 row = new BitArray(getWidth);
61 int[] pixelRow = image.getRGB(startX, y, getWidth, 1, null, 0, getWidth);
62 for (int i = 0; i < getWidth; i++) {
63 if (computeRGBLuminance(pixelRow[i]) < blackPoint) {
70 public int getHeight() {
71 return image.getHeight();
74 public int getWidth() {
75 return image.getWidth();
78 public void estimateBlackPoint(BlackPointEstimationMethod method, int argument) {
79 if (!method.equals(lastMethod) || argument != lastArgument) {
80 int width = image.getWidth();
81 int height = image.getHeight();
82 int[] histogram = new int[LUMINANCE_BUCKETS];
83 float biasTowardsWhite = 1.0f;
84 if (method.equals(BlackPointEstimationMethod.TWO_D_SAMPLING)) {
85 int minDimension = width < height ? width : height;
86 int startI = height == minDimension ? 0 : (height - width) >> 1;
87 int startJ = width == minDimension ? 0 : (width - height) >> 1;
88 for (int n = 0; n < minDimension; n++) {
89 int pixel = image.getRGB(startJ + n, startI + n);
90 histogram[computeRGBLuminance(pixel) >> LUMINANCE_SHIFT]++;
92 } else if (method.equals(BlackPointEstimationMethod.ROW_SAMPLING)) {
93 if (argument < 0 || argument >= height) {
94 throw new IllegalArgumentException("Row is not within the image: " + argument);
96 biasTowardsWhite = 2.0f;
97 int[] rgbArray = new int[width];
98 image.getRGB(0, argument, width, 1, rgbArray, 0, width);
99 for (int x = 0; x < width; x++) {
100 histogram[computeRGBLuminance(rgbArray[x]) >> LUMINANCE_SHIFT]++;
103 throw new IllegalArgumentException("Unknown method: " + method);
105 blackPoint = BlackPointEstimator.estimate(histogram, biasTowardsWhite) << LUMINANCE_SHIFT;
107 lastArgument = argument;
111 public BlackPointEstimationMethod getLastEstimationMethod() {
116 * Extracts luminance from a pixel from this source. By default, the source is assumed to use RGB,
117 * so this implementation computes luminance is a function of a red, green and blue components as
120 * <code>Y = 0.299R + 0.587G + 0.114B</code>
122 * where R, G, and B are values in [0,1].
124 private static int computeRGBLuminance(int pixel) {
125 // Coefficients add up to 1024 to make the divide into a fast shift
126 return (306 * ((pixel >> 16) & 0xFF) +
127 601 * ((pixel >> 8) & 0xFF) +
128 117 * (pixel & 0xFF)) >> 10;