@zxing/library
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TypeScript port of ZXing multi-format 1D/2D barcode image processing library.
225 lines (224 loc) • 11.8 kB
JavaScript
;
/*
* 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.
*/
var __extends = (this && this.__extends) || (function () {
var extendStatics = function (d, b) {
extendStatics = Object.setPrototypeOf ||
({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||
function (d, b) { for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p]; };
return extendStatics(d, b);
};
return function (d, b) {
extendStatics(d, b);
function __() { this.constructor = d; }
d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
};
})();
Object.defineProperty(exports, "__esModule", { value: true });
var GlobalHistogramBinarizer_1 = require("./GlobalHistogramBinarizer");
var BitMatrix_1 = require("./BitMatrix");
/**
* This class implements a local thresholding algorithm, which while slower than the
* GlobalHistogramBinarizer, is fairly efficient for what it does. It is designed for
* high frequency images of barcodes with black data on white backgrounds. For this application,
* it does a much better job than a global blackpoint with severe shadows and gradients.
* However it tends to produce artifacts on lower frequency images and is therefore not
* a good general purpose binarizer for uses outside ZXing.
*
* This class extends GlobalHistogramBinarizer, using the older histogram approach for 1D readers,
* and the newer local approach for 2D readers. 1D decoding using a per-row histogram is already
* inherently local, and only fails for horizontal gradients. We can revisit that problem later,
* but for now it was not a win to use local blocks for 1D.
*
* This Binarizer is the default for the unit tests and the recommended class for library users.
*
* @author dswitkin@google.com (Daniel Switkin)
*/
var HybridBinarizer = /** @class */ (function (_super) {
__extends(HybridBinarizer, _super);
function HybridBinarizer(source) {
var _this = _super.call(this, source) || this;
_this.matrix = null;
return _this;
}
/**
* Calculates the final BitMatrix once for all requests. This could be called once from the
* constructor instead, but there are some advantages to doing it lazily, such as making
* profiling easier, and not doing heavy lifting when callers don't expect it.
*/
/*@Override*/
HybridBinarizer.prototype.getBlackMatrix = function () {
if (this.matrix !== null) {
return this.matrix;
}
var source = this.getLuminanceSource();
var width = source.getWidth();
var height = source.getHeight();
if (width >= HybridBinarizer.MINIMUM_DIMENSION && height >= HybridBinarizer.MINIMUM_DIMENSION) {
var luminances = source.getMatrix();
var subWidth = width >> HybridBinarizer.BLOCK_SIZE_POWER;
if ((width & HybridBinarizer.BLOCK_SIZE_MASK) !== 0) {
subWidth++;
}
var subHeight = height >> HybridBinarizer.BLOCK_SIZE_POWER;
if ((height & HybridBinarizer.BLOCK_SIZE_MASK) !== 0) {
subHeight++;
}
var blackPoints = HybridBinarizer.calculateBlackPoints(luminances, subWidth, subHeight, width, height);
var newMatrix = new BitMatrix_1.default(width, height);
HybridBinarizer.calculateThresholdForBlock(luminances, subWidth, subHeight, width, height, blackPoints, newMatrix);
this.matrix = newMatrix;
}
else {
// If the image is too small, fall back to the global histogram approach.
this.matrix = _super.prototype.getBlackMatrix.call(this);
}
return this.matrix;
};
/*@Override*/
HybridBinarizer.prototype.createBinarizer = function (source) {
return new HybridBinarizer(source);
};
/**
* For each block in the image, calculate the average black point using a 5x5 grid
* of the blocks around it. Also handles the corner cases (fractional blocks are computed based
* on the last pixels in the row/column which are also used in the previous block).
*/
HybridBinarizer.calculateThresholdForBlock = function (luminances, subWidth /*int*/, subHeight /*int*/, width /*int*/, height /*int*/, blackPoints, matrix) {
var maxYOffset = height - HybridBinarizer.BLOCK_SIZE;
var maxXOffset = width - HybridBinarizer.BLOCK_SIZE;
for (var y = 0; y < subHeight; y++) {
var yoffset = y << HybridBinarizer.BLOCK_SIZE_POWER;
if (yoffset > maxYOffset) {
yoffset = maxYOffset;
}
var top_1 = HybridBinarizer.cap(y, 2, subHeight - 3);
for (var x = 0; x < subWidth; x++) {
var xoffset = x << HybridBinarizer.BLOCK_SIZE_POWER;
if (xoffset > maxXOffset) {
xoffset = maxXOffset;
}
var left = HybridBinarizer.cap(x, 2, subWidth - 3);
var sum = 0;
for (var z = -2; z <= 2; z++) {
var blackRow = blackPoints[top_1 + z];
sum += blackRow[left - 2] + blackRow[left - 1] + blackRow[left] + blackRow[left + 1] + blackRow[left + 2];
}
var average = sum / 25;
HybridBinarizer.thresholdBlock(luminances, xoffset, yoffset, average, width, matrix);
}
}
};
HybridBinarizer.cap = function (value /*int*/, min /*int*/, max /*int*/) {
return value < min ? min : value > max ? max : value;
};
/**
* Applies a single threshold to a block of pixels.
*/
HybridBinarizer.thresholdBlock = function (luminances, xoffset /*int*/, yoffset /*int*/, threshold /*int*/, stride /*int*/, matrix) {
for (var y = 0, offset = yoffset * stride + xoffset; y < HybridBinarizer.BLOCK_SIZE; y++, offset += stride) {
for (var x = 0; x < HybridBinarizer.BLOCK_SIZE; x++) {
// Comparison needs to be <= so that black == 0 pixels are black even if the threshold is 0.
if ((luminances[offset + x] & 0xFF) <= threshold) {
matrix.set(xoffset + x, yoffset + y);
}
}
}
};
/**
* Calculates a single black point for each block of pixels and saves it away.
* See the following thread for a discussion of this algorithm:
* http://groups.google.com/group/zxing/browse_thread/thread/d06efa2c35a7ddc0
*/
HybridBinarizer.calculateBlackPoints = function (luminances, subWidth /*int*/, subHeight /*int*/, width /*int*/, height /*int*/) {
var maxYOffset = height - HybridBinarizer.BLOCK_SIZE;
var maxXOffset = width - HybridBinarizer.BLOCK_SIZE;
// tslint:disable-next-line:whitespace
var blackPoints = new Array(subHeight); // subWidth
for (var y = 0; y < subHeight; y++) {
blackPoints[y] = new Int32Array(subWidth);
var yoffset = y << HybridBinarizer.BLOCK_SIZE_POWER;
if (yoffset > maxYOffset) {
yoffset = maxYOffset;
}
for (var x = 0; x < subWidth; x++) {
var xoffset = x << HybridBinarizer.BLOCK_SIZE_POWER;
if (xoffset > maxXOffset) {
xoffset = maxXOffset;
}
var sum = 0;
var min = 0xFF;
var max = 0;
for (var yy = 0, offset = yoffset * width + xoffset; yy < HybridBinarizer.BLOCK_SIZE; yy++, offset += width) {
for (var xx = 0; xx < HybridBinarizer.BLOCK_SIZE; xx++) {
var pixel = luminances[offset + xx] & 0xFF;
sum += pixel;
// still looking for good contrast
if (pixel < min) {
min = pixel;
}
if (pixel > max) {
max = pixel;
}
}
// short-circuit min/max tests once dynamic range is met
if (max - min > HybridBinarizer.MIN_DYNAMIC_RANGE) {
// finish the rest of the rows quickly
for (yy++, offset += width; yy < HybridBinarizer.BLOCK_SIZE; yy++, offset += width) {
for (var xx = 0; xx < HybridBinarizer.BLOCK_SIZE; xx++) {
sum += luminances[offset + xx] & 0xFF;
}
}
}
}
// The default estimate is the average of the values in the block.
var average = sum >> (HybridBinarizer.BLOCK_SIZE_POWER * 2);
if (max - min <= HybridBinarizer.MIN_DYNAMIC_RANGE) {
// If variation within the block is low, assume this is a block with only light or only
// dark pixels. In that case we do not want to use the average, as it would divide this
// low contrast area into black and white pixels, essentially creating data out of noise.
//
// The default assumption is that the block is light/background. Since no estimate for
// the level of dark pixels exists locally, use half the min for the block.
average = min / 2;
if (y > 0 && x > 0) {
// Correct the "white background" assumption for blocks that have neighbors by comparing
// the pixels in this block to the previously calculated black points. This is based on
// the fact that dark barcode symbology is always surrounded by some amount of light
// background for which reasonable black point estimates were made. The bp estimated at
// the boundaries is used for the interior.
// The (min < bp) is arbitrary but works better than other heuristics that were tried.
var averageNeighborBlackPoint = (blackPoints[y - 1][x] + (2 * blackPoints[y][x - 1]) + blackPoints[y - 1][x - 1]) / 4;
if (min < averageNeighborBlackPoint) {
average = averageNeighborBlackPoint;
}
}
}
blackPoints[y][x] = average;
}
}
return blackPoints;
};
// This class uses 5x5 blocks to compute local luminance, where each block is 8x8 pixels.
// So this is the smallest dimension in each axis we can accept.
HybridBinarizer.BLOCK_SIZE_POWER = 3;
HybridBinarizer.BLOCK_SIZE = 1 << HybridBinarizer.BLOCK_SIZE_POWER; // ...0100...00
HybridBinarizer.BLOCK_SIZE_MASK = HybridBinarizer.BLOCK_SIZE - 1; // ...0011...11
HybridBinarizer.MINIMUM_DIMENSION = HybridBinarizer.BLOCK_SIZE * 5;
HybridBinarizer.MIN_DYNAMIC_RANGE = 24;
return HybridBinarizer;
}(GlobalHistogramBinarizer_1.default));
exports.default = HybridBinarizer;