2 * Copyright 2007 ZXing authors
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 package com.google.zxing.common;
19 import com.google.zxing.NotFoundException;
22 * Implementations of this class can, given locations of finder patterns for a QR code in an
23 * image, sample the right points in the image to reconstruct the QR code, accounting for
24 * perspective distortion. It is abstracted since it is relatively expensive and should be allowed
25 * to take advantage of platform-specific optimized implementations, like Sun's Java Advanced
26 * Imaging library, but which may not be available in other environments such as J2ME, and vice
29 * The implementation used can be controlled by calling {@link #setGridSampler(GridSampler)}
30 * with an instance of a class which implements this interface.
34 public abstract class GridSampler {
36 private static GridSampler gridSampler = new DefaultGridSampler();
39 * Sets the implementation of {@link GridSampler} used by the library. One global
40 * instance is stored, which may sound problematic. But, the implementation provided
41 * ought to be appropriate for the entire platform, and all uses of this library
42 * in the whole lifetime of the JVM. For instance, an Android activity can swap in
43 * an implementation that takes advantage of native platform libraries.
45 * @param newGridSampler The platform-specific object to install.
47 public static void setGridSampler(GridSampler newGridSampler) {
48 if (newGridSampler == null) {
49 throw new IllegalArgumentException();
51 gridSampler = newGridSampler;
55 * @return the current implementation of {@link GridSampler}
57 public static GridSampler getInstance() {
62 * <p>Samples an image for a square matrix of bits of the given dimension. This is used to extract
63 * the black/white modules of a 2D barcode like a QR Code found in an image. Because this barcode
64 * may be rotated or perspective-distorted, the caller supplies four points in the source image
65 * that define known points in the barcode, so that the image may be sampled appropriately.</p>
67 * <p>The last eight "from" parameters are four X/Y coordinate pairs of locations of points in
68 * the image that define some significant points in the image to be sample. For example,
69 * these may be the location of finder pattern in a QR Code.</p>
71 * <p>The first eight "to" parameters are four X/Y coordinate pairs measured in the destination
72 * {@link BitMatrix}, from the top left, where the known points in the image given by the "from"
73 * parameters map to.</p>
75 * <p>These 16 parameters define the transformation needed to sample the image.</p>
77 * @param image image to sample
78 * @param dimension width/height of {@link BitMatrix} to sample from image
79 * @return {@link BitMatrix} representing a grid of points sampled from the image within a region
80 * defined by the "from" parameters
81 * @throws NotFoundException if image can't be sampled, for example, if the transformation defined
82 * by the given points is invalid or results in sampling outside the image boundaries
84 public abstract BitMatrix sampleGrid(BitMatrix image,
86 float p1ToX, float p1ToY,
87 float p2ToX, float p2ToY,
88 float p3ToX, float p3ToY,
89 float p4ToX, float p4ToY,
90 float p1FromX, float p1FromY,
91 float p2FromX, float p2FromY,
92 float p3FromX, float p3FromY,
93 float p4FromX, float p4FromY) throws NotFoundException;
95 public BitMatrix sampleGrid(BitMatrix image,
97 PerspectiveTransform transform) throws NotFoundException {
98 throw new IllegalStateException(); // Can't use UnsupportedOperationException
103 * <p>Checks a set of points that have been transformed to sample points on an image against
104 * the image's dimensions to see if the point are even within the image.</p>
106 * <p>This method will actually "nudge" the endpoints back onto the image if they are found to be
107 * barely (less than 1 pixel) off the image. This accounts for imperfect detection of finder
108 * patterns in an image where the QR Code runs all the way to the image border.</p>
110 * <p>For efficiency, the method will check points from either end of the line until one is found
111 * to be within the image. Because the set of points are assumed to be linear, this is valid.</p>
113 * @param image image into which the points should map
114 * @param points actual points in x1,y1,...,xn,yn form
115 * @throws NotFoundException if an endpoint is lies outside the image boundaries
117 protected static void checkAndNudgePoints(BitMatrix image, float[] points)
118 throws NotFoundException {
119 int width = image.getWidth();
120 int height = image.getHeight();
121 // Check and nudge points from start until we see some that are OK:
122 boolean nudged = true;
123 for (int offset = 0; offset < points.length && nudged; offset += 2) {
124 int x = (int) points[offset];
125 int y = (int) points[offset + 1];
126 if (x < -1 || x > width || y < -1 || y > height) {
127 throw NotFoundException.getNotFoundInstance();
131 points[offset] = 0.0f;
133 } else if (x == width) {
134 points[offset] = width - 1;
138 points[offset + 1] = 0.0f;
140 } else if (y == height) {
141 points[offset + 1] = height - 1;
145 // Check and nudge points from end:
147 for (int offset = points.length - 2; offset >= 0 && nudged; offset -= 2) {
148 int x = (int) points[offset];
149 int y = (int) points[offset + 1];
150 if (x < -1 || x > width || y < -1 || y > height) {
151 throw NotFoundException.getNotFoundInstance();
155 points[offset] = 0.0f;
157 } else if (x == width) {
158 points[offset] = width - 1;
162 points[offset + 1] = 0.0f;
164 } else if (y == height) {
165 points[offset + 1] = height - 1;