/*
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* Copyright 2009 ZXing authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/*namespace com.google.zxing.common {*/
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import Binarizer from '../Binarizer';
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import BitArray from './BitArray';
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import BitMatrix from './BitMatrix';
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import NotFoundException from '../NotFoundException';
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/**
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* This Binarizer implementation uses the old ZXing global histogram approach. It is suitable
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* for low-end mobile devices which don't have enough CPU or memory to use a local thresholding
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* algorithm. However, because it picks a global black point, it cannot handle difficult shadows
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* and gradients.
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*
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* Faster mobile devices and all desktop applications should probably use HybridBinarizer instead.
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*
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* @author dswitkin@google.com (Daniel Switkin)
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* @author Sean Owen
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*/
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export default class GlobalHistogramBinarizer extends Binarizer {
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constructor(source) {
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super(source);
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this.luminances = GlobalHistogramBinarizer.EMPTY;
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this.buckets = new Int32Array(GlobalHistogramBinarizer.LUMINANCE_BUCKETS);
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}
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// Applies simple sharpening to the row data to improve performance of the 1D Readers.
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/*@Override*/
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getBlackRow(y /*int*/, row) {
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const source = this.getLuminanceSource();
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const width = source.getWidth();
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if (row === undefined || row === null || row.getSize() < width) {
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row = new BitArray(width);
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}
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else {
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row.clear();
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}
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this.initArrays(width);
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const localLuminances = source.getRow(y, this.luminances);
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const localBuckets = this.buckets;
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for (let x = 0; x < width; x++) {
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localBuckets[(localLuminances[x] & 0xff) >> GlobalHistogramBinarizer.LUMINANCE_SHIFT]++;
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}
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const blackPoint = GlobalHistogramBinarizer.estimateBlackPoint(localBuckets);
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if (width < 3) {
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// Special case for very small images
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for (let x = 0; x < width; x++) {
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if ((localLuminances[x] & 0xff) < blackPoint) {
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row.set(x);
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}
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}
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}
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else {
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let left = localLuminances[0] & 0xff;
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let center = localLuminances[1] & 0xff;
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for (let x = 1; x < width - 1; x++) {
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const right = localLuminances[x + 1] & 0xff;
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// A simple -1 4 -1 box filter with a weight of 2.
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if (((center * 4) - left - right) / 2 < blackPoint) {
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row.set(x);
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}
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left = center;
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center = right;
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}
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}
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return row;
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}
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// Does not sharpen the data, as this call is intended to only be used by 2D Readers.
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/*@Override*/
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getBlackMatrix() {
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const source = this.getLuminanceSource();
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const width = source.getWidth();
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const height = source.getHeight();
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const matrix = new BitMatrix(width, height);
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// Quickly calculates the histogram by sampling four rows from the image. This proved to be
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// more robust on the blackbox tests than sampling a diagonal as we used to do.
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this.initArrays(width);
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const localBuckets = this.buckets;
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for (let y = 1; y < 5; y++) {
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const row = Math.floor((height * y) / 5);
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const localLuminances = source.getRow(row, this.luminances);
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const right = Math.floor((width * 4) / 5);
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for (let x = Math.floor(width / 5); x < right; x++) {
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const pixel = localLuminances[x] & 0xff;
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localBuckets[pixel >> GlobalHistogramBinarizer.LUMINANCE_SHIFT]++;
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}
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}
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const blackPoint = GlobalHistogramBinarizer.estimateBlackPoint(localBuckets);
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// We delay reading the entire image luminance until the black point estimation succeeds.
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// Although we end up reading four rows twice, it is consistent with our motto of
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// "fail quickly" which is necessary for continuous scanning.
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const localLuminances = source.getMatrix();
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for (let y = 0; y < height; y++) {
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const offset = y * width;
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for (let x = 0; x < width; x++) {
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const pixel = localLuminances[offset + x] & 0xff;
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if (pixel < blackPoint) {
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matrix.set(x, y);
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}
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}
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}
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return matrix;
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}
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/*@Override*/
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createBinarizer(source) {
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return new GlobalHistogramBinarizer(source);
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}
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initArrays(luminanceSize /*int*/) {
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if (this.luminances.length < luminanceSize) {
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this.luminances = new Uint8ClampedArray(luminanceSize);
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}
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const buckets = this.buckets;
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for (let x = 0; x < GlobalHistogramBinarizer.LUMINANCE_BUCKETS; x++) {
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buckets[x] = 0;
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}
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}
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static estimateBlackPoint(buckets) {
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// Find the tallest peak in the histogram.
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const numBuckets = buckets.length;
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let maxBucketCount = 0;
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let firstPeak = 0;
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let firstPeakSize = 0;
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for (let x = 0; x < numBuckets; x++) {
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if (buckets[x] > firstPeakSize) {
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firstPeak = x;
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firstPeakSize = buckets[x];
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}
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if (buckets[x] > maxBucketCount) {
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maxBucketCount = buckets[x];
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}
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}
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// Find the second-tallest peak which is somewhat far from the tallest peak.
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let secondPeak = 0;
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let secondPeakScore = 0;
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for (let x = 0; x < numBuckets; x++) {
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const distanceToBiggest = x - firstPeak;
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// Encourage more distant second peaks by multiplying by square of distance.
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const score = buckets[x] * distanceToBiggest * distanceToBiggest;
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if (score > secondPeakScore) {
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secondPeak = x;
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secondPeakScore = score;
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}
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}
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// Make sure firstPeak corresponds to the black peak.
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if (firstPeak > secondPeak) {
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const temp = firstPeak;
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firstPeak = secondPeak;
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secondPeak = temp;
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}
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// If there is too little contrast in the image to pick a meaningful black point, throw rather
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// than waste time trying to decode the image, and risk false positives.
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if (secondPeak - firstPeak <= numBuckets / 16) {
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throw new NotFoundException();
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}
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// Find a valley between them that is low and closer to the white peak.
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let bestValley = secondPeak - 1;
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let bestValleyScore = -1;
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for (let x = secondPeak - 1; x > firstPeak; x--) {
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const fromFirst = x - firstPeak;
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const score = fromFirst * fromFirst * (secondPeak - x) * (maxBucketCount - buckets[x]);
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if (score > bestValleyScore) {
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bestValley = x;
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bestValleyScore = score;
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}
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}
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return bestValley << GlobalHistogramBinarizer.LUMINANCE_SHIFT;
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}
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}
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GlobalHistogramBinarizer.LUMINANCE_BITS = 5;
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GlobalHistogramBinarizer.LUMINANCE_SHIFT = 8 - GlobalHistogramBinarizer.LUMINANCE_BITS;
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GlobalHistogramBinarizer.LUMINANCE_BUCKETS = 1 << GlobalHistogramBinarizer.LUMINANCE_BITS;
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GlobalHistogramBinarizer.EMPTY = Uint8ClampedArray.from([0]);
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