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Diffstat (limited to 'libraries/zxing/src/com/google/zxing/common/GlobalHistogramBinarizer.java')
-rw-r--r-- | libraries/zxing/src/com/google/zxing/common/GlobalHistogramBinarizer.java | 194 |
1 files changed, 194 insertions, 0 deletions
diff --git a/libraries/zxing/src/com/google/zxing/common/GlobalHistogramBinarizer.java b/libraries/zxing/src/com/google/zxing/common/GlobalHistogramBinarizer.java new file mode 100644 index 000000000..4fa2a887b --- /dev/null +++ b/libraries/zxing/src/com/google/zxing/common/GlobalHistogramBinarizer.java @@ -0,0 +1,194 @@ +/* + * 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.common; + +import com.google.zxing.Binarizer; +import com.google.zxing.LuminanceSource; +import com.google.zxing.NotFoundException; + +/** + * This Binarizer implementation uses the old ZXing global histogram approach. It is suitable + * for low-end mobile devices which don't have enough CPU or memory to use a local thresholding + * algorithm. However, because it picks a global black point, it cannot handle difficult shadows + * and gradients. + * + * Faster mobile devices and all desktop applications should probably use HybridBinarizer instead. + * + * @author dswitkin@google.com (Daniel Switkin) + * @author Sean Owen + */ +public class GlobalHistogramBinarizer extends Binarizer { + + private static final int LUMINANCE_BITS = 5; + private static final int LUMINANCE_SHIFT = 8 - LUMINANCE_BITS; + private static final int LUMINANCE_BUCKETS = 1 << LUMINANCE_BITS; + + private byte[] luminances = null; + private int[] buckets = null; + + public GlobalHistogramBinarizer(LuminanceSource source) { + super(source); + } + + // Applies simple sharpening to the row data to improve performance of the 1D Readers. + public BitArray getBlackRow(int y, BitArray row) throws NotFoundException { + LuminanceSource source = getLuminanceSource(); + int width = source.getWidth(); + if (row == null || row.getSize() < width) { + row = new BitArray(width); + } else { + row.clear(); + } + + initArrays(width); + byte[] localLuminances = source.getRow(y, luminances); + int[] localBuckets = buckets; + for (int x = 0; x < width; x++) { + int pixel = localLuminances[x] & 0xff; + localBuckets[pixel >> LUMINANCE_SHIFT]++; + } + int blackPoint = estimateBlackPoint(localBuckets); + + int left = localLuminances[0] & 0xff; + int center = localLuminances[1] & 0xff; + for (int x = 1; x < width - 1; x++) { + int right = localLuminances[x + 1] & 0xff; + // A simple -1 4 -1 box filter with a weight of 2. + int luminance = ((center << 2) - left - right) >> 1; + if (luminance < blackPoint) { + row.set(x); + } + left = center; + center = right; + } + return row; + } + + // Does not sharpen the data, as this call is intended to only be used by 2D Readers. + public BitMatrix getBlackMatrix() throws NotFoundException { + LuminanceSource source = getLuminanceSource(); + int width = source.getWidth(); + int height = source.getHeight(); + BitMatrix matrix = new BitMatrix(width, height); + + // Quickly calculates the histogram by sampling four rows from the image. This proved to be + // more robust on the blackbox tests than sampling a diagonal as we used to do. + initArrays(width); + int[] localBuckets = buckets; + for (int y = 1; y < 5; y++) { + int row = height * y / 5; + byte[] localLuminances = source.getRow(row, luminances); + int right = (width << 2) / 5; + for (int x = width / 5; x < right; x++) { + int pixel = localLuminances[x] & 0xff; + localBuckets[pixel >> LUMINANCE_SHIFT]++; + } + } + int blackPoint = estimateBlackPoint(localBuckets); + + // We delay reading the entire image luminance until the black point estimation succeeds. + // Although we end up reading four rows twice, it is consistent with our motto of + // "fail quickly" which is necessary for continuous scanning. + byte[] localLuminances = source.getMatrix(); + for (int y = 0; y < height; y++) { + int offset = y * width; + for (int x = 0; x< width; x++) { + int pixel = localLuminances[offset + x] & 0xff; + if (pixel < blackPoint) { + matrix.set(x, y); + } + } + } + + return matrix; + } + + public Binarizer createBinarizer(LuminanceSource source) { + return new GlobalHistogramBinarizer(source); + } + + private void initArrays(int luminanceSize) { + if (luminances == null || luminances.length < luminanceSize) { + luminances = new byte[luminanceSize]; + } + if (buckets == null) { + buckets = new int[LUMINANCE_BUCKETS]; + } else { + for (int x = 0; x < LUMINANCE_BUCKETS; x++) { + buckets[x] = 0; + } + } + } + + private static int estimateBlackPoint(int[] buckets) throws NotFoundException { + // Find the tallest peak in the histogram. + int numBuckets = buckets.length; + int maxBucketCount = 0; + int firstPeak = 0; + int firstPeakSize = 0; + for (int x = 0; x < numBuckets; x++) { + if (buckets[x] > firstPeakSize) { + firstPeak = x; + firstPeakSize = buckets[x]; + } + if (buckets[x] > maxBucketCount) { + maxBucketCount = buckets[x]; + } + } + + // Find the second-tallest peak which is somewhat far from the tallest peak. + int secondPeak = 0; + int secondPeakScore = 0; + for (int x = 0; x < numBuckets; x++) { + int distanceToBiggest = x - firstPeak; + // Encourage more distant second peaks by multiplying by square of distance. + int score = buckets[x] * distanceToBiggest * distanceToBiggest; + if (score > secondPeakScore) { + secondPeak = x; + secondPeakScore = score; + } + } + + // Make sure firstPeak corresponds to the black peak. + if (firstPeak > secondPeak) { + int temp = firstPeak; + firstPeak = secondPeak; + secondPeak = temp; + } + + // If there is too little contrast in the image to pick a meaningful black point, throw rather + // than waste time trying to decode the image, and risk false positives. + if (secondPeak - firstPeak <= numBuckets >> 4) { + throw NotFoundException.getNotFoundInstance(); + } + + // Find a valley between them that is low and closer to the white peak. + int bestValley = secondPeak - 1; + int bestValleyScore = -1; + for (int x = secondPeak - 1; x > firstPeak; x--) { + int fromFirst = x - firstPeak; + int score = fromFirst * fromFirst * (secondPeak - x) * (maxBucketCount - buckets[x]); + if (score > bestValleyScore) { + bestValley = x; + bestValleyScore = score; + } + } + + return bestValley << LUMINANCE_SHIFT; + } + +} |