--- /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.ReaderException;
+
+/**
+ * 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)
+ */
+public final class HybridBinarizer extends GlobalHistogramBinarizer {
+
+ // 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.
+ private static final int MINIMUM_DIMENSION = 40;
+
+ private BitMatrix matrix = null;
+
+ public HybridBinarizer(LuminanceSource source) {
+ super(source);
+ }
+
+ public BitMatrix getBlackMatrix() throws ReaderException {
+ binarizeEntireImage();
+ return matrix;
+ }
+
+ public Binarizer createBinarizer(LuminanceSource source) {
+ return new HybridBinarizer(source);
+ }
+
+ // 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.
+ private void binarizeEntireImage() throws ReaderException {
+ if (matrix == null) {
+ LuminanceSource source = getLuminanceSource();
+ if (source.getWidth() >= MINIMUM_DIMENSION && source.getHeight() >= MINIMUM_DIMENSION) {
+ byte[] luminances = source.getMatrix();
+ int width = source.getWidth();
+ int height = source.getHeight();
+ int subWidth = width >> 3;
+ int subHeight = height >> 3;
+ int[][] blackPoints = calculateBlackPoints(luminances, subWidth, subHeight, width);
+
+ matrix = new BitMatrix(width, height);
+ calculateThresholdForBlock(luminances, subWidth, subHeight, width, blackPoints, matrix);
+ } else {
+ // If the image is too small, fall back to the global histogram approach.
+ matrix = super.getBlackMatrix();
+ }
+ }
+ }
+
+ // For each 8x8 block in the image, calculate the average black point using a 5x5 grid
+ // of the blocks around it. Also handles the corner cases, but will ignore up to 7 pixels
+ // on the right edge and 7 pixels at the bottom of the image if the overall dimensions are not
+ // multiples of eight. In practice, leaving those pixels white does not seem to be a problem.
+ private static void calculateThresholdForBlock(byte[] luminances, int subWidth, int subHeight,
+ int stride, int[][] blackPoints, BitMatrix matrix) {
+ for (int y = 0; y < subHeight; y++) {
+ for (int x = 0; x < subWidth; x++) {
+ int left = (x > 1) ? x : 2;
+ left = (left < subWidth - 2) ? left : subWidth - 3;
+ int top = (y > 1) ? y : 2;
+ top = (top < subHeight - 2) ? top : subHeight - 3;
+ int sum = 0;
+ for (int z = -2; z <= 2; z++) {
+ sum += blackPoints[top + z][left - 2];
+ sum += blackPoints[top + z][left - 1];
+ sum += blackPoints[top + z][left];
+ sum += blackPoints[top + z][left + 1];
+ sum += blackPoints[top + z][left + 2];
+ }
+ int average = sum / 25;
+ threshold8x8Block(luminances, x << 3, y << 3, average, stride, matrix);
+ }
+ }
+ }
+
+ // Applies a single threshold to an 8x8 block of pixels.
+ private static void threshold8x8Block(byte[] luminances, int xoffset, int yoffset, int threshold,
+ int stride, BitMatrix matrix) {
+ for (int y = 0; y < 8; y++) {
+ int offset = (yoffset + y) * stride + xoffset;
+ for (int x = 0; x < 8; x++) {
+ int pixel = luminances[offset + x] & 0xff;
+ if (pixel < threshold) {
+ matrix.set(xoffset + x, yoffset + y);
+ }
+ }
+ }
+ }
+
+ // Calculates a single black point for each 8x8 block of pixels and saves it away.
+ private static int[][] calculateBlackPoints(byte[] luminances, int subWidth, int subHeight,
+ int stride) {
+ int[][] blackPoints = new int[subHeight][subWidth];
+ for (int y = 0; y < subHeight; y++) {
+ for (int x = 0; x < subWidth; x++) {
+ int sum = 0;
+ int min = 255;
+ int max = 0;
+ for (int yy = 0; yy < 8; yy++) {
+ int offset = ((y << 3) + yy) * stride + (x << 3);
+ for (int xx = 0; xx < 8; xx++) {
+ int pixel = luminances[offset + xx] & 0xff;
+ sum += pixel;
+ if (pixel < min) {
+ min = pixel;
+ }
+ if (pixel > max) {
+ max = pixel;
+ }
+ }
+ }
+
+ // If the contrast is inadequate, use half the minimum, so that this block will be
+ // treated as part of the white background, but won't drag down neighboring blocks
+ // too much.
+ int average = (max - min > 24) ? (sum >> 6) : (min >> 1);
+ blackPoints[y][x] = average;
+ }
+ }
+ return blackPoints;
+ }
+
+}
projects / zxing.git / blobdiff