--- /dev/null
+/*
+ * 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 static final byte[] EMPTY = new byte[0];
+
+ private byte[] luminances;
+ private final int[] buckets;
+
+ public GlobalHistogramBinarizer(LuminanceSource source) {
+ super(source);
+ luminances = EMPTY;
+ buckets = new int[LUMINANCE_BUCKETS];
+ }
+
+ // Applies simple sharpening to the row data to improve performance of the 1D Readers.
+ @Override
+ 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.
+ @Override
+ 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;
+ }
+
+ @Override
+ public Binarizer createBinarizer(LuminanceSource source) {
+ return new GlobalHistogramBinarizer(source);
+ }
+
+ private void initArrays(int luminanceSize) {
+ if (luminances.length < luminanceSize) {
+ luminances = new byte[luminanceSize];
+ }
+ 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;
+ }
+
+}
projects / ~andy / freeotp / blobdiff