2 * Copyright (C) 2008 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.android;
19 import android.graphics.Bitmap;
20 import com.google.zxing.BlackPointEstimationMethod;
21 import com.google.zxing.MonochromeBitmapSource;
22 import com.google.zxing.ReaderException;
23 import com.google.zxing.common.BitArray;
24 import com.google.zxing.common.BlackPointEstimator;
27 * This object implements MonochromeBitmapSource around an Android Bitmap. Rather than capturing an
28 * RGB image and calculating the grey value at each pixel, we ask the camera driver for YUV data and
29 * strip out the luminance channel directly. This should be faster but provides fewer bits, i.e.
32 * @author dswitkin@google.com (Daniel Switkin)
33 * @author srowen@google.com (Sean Owen)
35 final class RGBMonochromeBitmapSource implements MonochromeBitmapSource {
37 private final Bitmap image;
38 private int blackPoint;
39 private BlackPointEstimationMethod lastMethod;
40 private int lastArgument;
42 private static final int LUMINANCE_BITS = 5;
43 private static final int LUMINANCE_SHIFT = 8 - LUMINANCE_BITS;
44 private static final int LUMINANCE_BUCKETS = 1 << LUMINANCE_BITS;
46 RGBMonochromeBitmapSource(Bitmap image) {
53 public boolean isBlack(int x, int y) {
54 return computeRGBLuminance(image.getPixel(x, y)) < blackPoint;
57 public BitArray getBlackRow(int y, BitArray row, int startX, int getWidth) {
59 row = new BitArray(getWidth);
63 int[] pixelRow = new int[getWidth];
64 image.getPixels(pixelRow, 0, getWidth, startX, y, getWidth, 1);
65 for (int i = 0; i < getWidth; i++) {
66 if (computeRGBLuminance(pixelRow[i]) < blackPoint) {
73 public int getHeight() {
74 return image.height();
77 public int getWidth() {
81 public void estimateBlackPoint(BlackPointEstimationMethod method, int argument) throws ReaderException {
82 if (!method.equals(lastMethod) || argument != lastArgument) {
83 int width = image.width();
84 int height = image.height();
85 int[] histogram = new int[LUMINANCE_BUCKETS];
86 if (method.equals(BlackPointEstimationMethod.TWO_D_SAMPLING)) {
87 int minDimension = width < height ? width : height;
88 int startI = height == minDimension ? 0 : (height - width) >> 1;
89 int startJ = width == minDimension ? 0 : (width - height) >> 1;
90 for (int n = 0; n < minDimension; n++) {
91 int pixel = image.getPixel(startJ + n, startI + n);
92 histogram[computeRGBLuminance(pixel) >> LUMINANCE_SHIFT]++;
94 } else if (method.equals(BlackPointEstimationMethod.ROW_SAMPLING)) {
95 if (argument < 0 || argument >= height) {
96 throw new IllegalArgumentException("Row is not within the image: " + argument);
98 int[] pixelRow = new int[width];
99 image.getPixels(pixelRow, 0, width, 0, argument, width, 1);
100 for (int x = 0; x < width; x++) {
101 histogram[computeRGBLuminance(pixelRow[x]) >> LUMINANCE_SHIFT]++;
104 throw new IllegalArgumentException("Unknown method: " + method);
106 blackPoint = BlackPointEstimator.estimate(histogram) << LUMINANCE_SHIFT;
108 lastArgument = argument;
112 public BlackPointEstimationMethod getLastEstimationMethod() {
116 public MonochromeBitmapSource rotateCounterClockwise() {
117 throw new IllegalStateException("Rotate not supported");
120 public boolean isRotateSupported() {
125 * An optimized approximation of a more proper conversion from RGB to luminance which
126 * only uses shifts. See BufferedImageMonochromeBitmapSource for an original version.
128 private static int computeRGBLuminance(int pixel) {
129 // Instead of multiplying by 306, 601, 117, we multiply by 256, 512, 256, so that
130 // the multiplies can be implemented as shifts.
134 // return ((((pixel >> 16) & 0xFF) << 8) +
135 // (((pixel >> 8) & 0xFF) << 9) +
136 // (( pixel & 0xFF) << 8)) >> 10;
138 // That is, we're replacing the coefficients in the original with powers of two,
139 // which can be implemented as shifts, even though changing the coefficients slightly
140 // corrupts the conversion. Not significant for our purposes.
142 // But we can get even cleverer and eliminate a few shifts:
143 return (((pixel & 0x00FF0000) >> 16) +
144 ((pixel & 0x0000FF00) >> 7) +
145 ( pixel & 0x000000FF )) >> 2;