zxing/csharp/pdf417/detector/Detector.cs

/*
 * 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.
 */

using System;
using System.Collections.Generic;

using ZXing.Common;
using ZXing.Common.Detector;
using System.Linq;

namespace ZXing.PDF417.Internal
{
    /// <summary>
    /// <p>Encapsulates logic that can detect a PDF417 Code in an image, even if the
    /// PDF417 Code is rotated or skewed, or partially obscured.</p>
    ///
    /// <author>SITA Lab (kevin.osullivan@sita.aero)</author>
    /// <author>dswitkin@google.com (Daniel Switkin)</author>
    /// <author> Guenther Grau (Java Core) - changed this class from an instance to static methods</author>
    /// <author> Stephen Furlani (C# Port)</author>
    /// </summary>
    public sealed class Detector
    {
        private static readonly int[] INDEXES_START_PATTERN = {0, 4, 1, 5};
        private static readonly int[] INDEXES_STOP_PATTERN = {6, 2, 7, 3};
        private static readonly int INTEGER_MATH_SHIFT = 8;
        private static readonly int PATTERN_MATCH_RESULT_SCALE_FACTOR = 1 << INTEGER_MATH_SHIFT;
        private static readonly int MAX_AVG_VARIANCE = (int)(PATTERN_MATCH_RESULT_SCALE_FACTOR * 0.42f);
        private static readonly int MAX_INDIVIDUAL_VARIANCE = (int)(PATTERN_MATCH_RESULT_SCALE_FACTOR * 0.8f);
        

        /// <summary>
        /// B S B S B S B S Bar/Space pattern
        /// 11111111 0 1 0 1 0 1 000.
        /// </summary>
        private static readonly int[] START_PATTERN = {8, 1, 1, 1, 1, 1, 1, 3};
        /// <summary>
        /// 1111111 0 1 000 1 0 1 00 1
        /// </summary>
        private static readonly int[] STOP_PATTERN = {7, 1, 1, 3, 1, 1, 1, 2, 1};
        private static readonly int MAX_PIXEL_DRIFT = 3;
        private static readonly int MAX_PATTERN_DRIFT = 5;
        /// <summary>
        /// if we set the value too low, then we don't detect the correct height of the bar if the start patterns are damaged.
        /// if we set the value too high, then we might detect the start pattern from a neighbor barcode.
        /// </summary>
        private static readonly int SKIPPED_ROW_COUNT_MAX = 25;
        /// <summary>
        /// A PDF471 barcode should have at least 3 rows, with each row being >= 3 times the module width. Therefore it should be at least
        /// 9 pixels tall. To be conservative, we use about half the size to ensure we don't miss it.
        /// </summary>
        private static readonly int ROW_STEP = 5;
        private static readonly int BARCODE_MIN_HEIGHT = 10;

        /// <summary>
        /// <p>Detects a PDF417 Code in an image. Only checks 0 and 180 degree rotations.</p>
        /// </summary>
        /// <param name="image">Image.</param>
        /// <param name="hints">Hints.</param>
        /// <param name="multiple">If set to <c>true</c> multiple.</param>
        /// <returns><see cref="PDF417DetectorResult"/> encapsulating results of detecting a PDF417 code </returns>
        public static PDF417DetectorResult Detect(BinaryBitmap image,IDictionary<DecodeHintType,object> hints, bool multiple) {
            // TODO detection improvement, tryHarder could try several different luminance thresholds/blackpoints or even 
            // different binarizers (SF: or different Skipped Row Counts/Steps?)
            //boolean tryHarder = hints != null && hints.containsKey(DecodeHintType.TRY_HARDER);
            
            BitMatrix bitMatrix = image.BlackMatrix;
            
            List<ResultPoint[]> barcodeCoordinates = Detect(multiple, bitMatrix);
            if (barcodeCoordinates.Count == 0) {
                bitMatrix.Rotate180();
                barcodeCoordinates = Detect(multiple, bitMatrix);
            }
            return new PDF417DetectorResult(bitMatrix, barcodeCoordinates);
        }
        /// <summary>
        /// Detects PDF417 codes in an image. Only checks 0 degree rotation (so rotate the matrix and check again outside of this method)
        /// </summary>
        /// <param name="multiple">multiple if true, then the image is searched for multiple codes. If false, then at most one code will be found and returned.</param>
        /// <param name="bitMatrix">bitMatrix bit matrix to detect barcodes in.</param>
        /// <returns>List of ResultPoint arrays containing the coordinates of found barcodes</returns>
        private static List<ResultPoint[]> Detect(bool multiple, BitMatrix bitMatrix) {
            List<ResultPoint[]> barcodeCoordinates = new List<ResultPoint[]>();
            int row = 0;
            int column = 0;
            bool foundBarcodeInRow = false;
            while (row < bitMatrix.Height) {
                ResultPoint[] vertices = FindVertices(bitMatrix, row, column);
                
                if (vertices[0] == null && vertices[3] == null) {
                    if (!foundBarcodeInRow) {
                        // we didn't find any barcode so that's the end of searching 
                        break;
                    }
                    // we didn't find a barcode starting at the given column and row. Try again from the first column and slightly
                    // below the lowest barcode we found so far.
                    foundBarcodeInRow = false;
                    column = 0;
                    foreach (ResultPoint[] barcodeCoordinate in barcodeCoordinates) {
                        if (barcodeCoordinate[1] != null) {
                            row = (int) Math.Max(row, barcodeCoordinate[1].Y);
                        }
                        if (barcodeCoordinate[3] != null) {
                            row = Math.Max(row, (int) barcodeCoordinate[3].Y);
                        }
                    }
                    row += ROW_STEP;
                    continue;
                }
                foundBarcodeInRow = true;
                barcodeCoordinates.Add(vertices);
                if (!multiple) {
                    break;
                }
                // if we didn't find a right row indicator column, then continue the search for the next barcode after the 
                // start pattern of the barcode just found.
                if (vertices[2] != null) {
                    column = (int) vertices[2].X;
                    row = (int) vertices[2].Y;
                } else {
                    column = (int) vertices[4].X;
                    row = (int) vertices[4].Y;
                }
            }
            return barcodeCoordinates;
        }
 
        /// <summary>
        /// Locate the vertices and the codewords area of a black blob using the Start and Stop patterns as locators.
        /// </summary>
        /// <param name="matrix">Matrix.</param>
        /// <param name="startRow">Start row.</param>
        /// <param name="startColumn">Start column.</param>
        /// <returns> an array containing the vertices:
        ///           vertices[0] x, y top left barcode
        ///           vertices[1] x, y bottom left barcode
        ///           vertices[2] x, y top right barcode
        ///           vertices[3] x, y bottom right barcode
        ///           vertices[4] x, y top left codeword area
        ///           vertices[5] x, y bottom left codeword area
        ///           vertices[6] x, y top right codeword area
        ///           vertices[7] x, y bottom right codeword area
        /// </returns>
        private static ResultPoint[] FindVertices(BitMatrix matrix, int startRow, int startColumn) {
            int height = matrix.Height;
            int width = matrix.Width;

            ResultPoint[] result = new ResultPoint[8];
            CopyToResult(result, FindRowsWithPattern(matrix, height, width, startRow, startColumn, START_PATTERN),
                         INDEXES_START_PATTERN);
            
            if (result[4] != null) {
                startColumn = (int) result[4].X;
                startRow = (int) result[4].Y;
            }
            CopyToResult(result, FindRowsWithPattern(matrix, height, width, startRow, startColumn, STOP_PATTERN),
                         INDEXES_STOP_PATTERN);
            return result;
        }

        /// <summary>
        /// Copies the temp data to the final result
        /// </summary>
        /// <param name="result">Result.</param>
        /// <param name="tmpResult">Temp result.</param>
        /// <param name="destinationIndexes">Destination indexes.</param>
        private static void CopyToResult(ResultPoint[] result, ResultPoint[] tmpResult, int[] destinationIndexes) {
            for (int i = 0; i < destinationIndexes.Length; i++) {
                result[destinationIndexes[i]] = tmpResult[i];
            }
        }

        /// <summary>
        /// Finds the rows with the given pattern.
        /// </summary>
        /// <returns>The rows with pattern.</returns>
        /// <param name="matrix">Matrix.</param>
        /// <param name="height">Height.</param>
        /// <param name="width">Width.</param>
        /// <param name="startRow">Start row.</param>
        /// <param name="startColumn">Start column.</param>
        /// <param name="pattern">Pattern.</param>
        private static ResultPoint[] FindRowsWithPattern(
            BitMatrix matrix,
            int height,
            int width,
            int startRow,
            int startColumn,
            int[] pattern) {
            ResultPoint[] result = new ResultPoint[4];
            bool found = false;
            int[] counters = new int[pattern.Length];
            for (; startRow < height; startRow += ROW_STEP) {
                int[] loc = FindGuardPattern(matrix, startColumn, startRow, width, false, pattern, counters);
                if (loc != null) {
                    while (startRow > 0) {
                        int[] previousRowLoc = FindGuardPattern(matrix, startColumn, --startRow, width, false, pattern, counters);
                        if (previousRowLoc != null) {
                            loc = previousRowLoc;
                        } else {
                            startRow++;
                            break;
                        }
                    }
                    result[0] = new ResultPoint(loc[0], startRow);
                    result[1] = new ResultPoint(loc[1], startRow);
                    found = true;
                    break;
                }
            }
            int stopRow = startRow + 1;
            // Last row of the current symbol that contains pattern
            if (found) {
                int skippedRowCount = 0;
                int[] previousRowLoc = {(int) result[0].X, (int) result[1].X};
                for (; stopRow < height; stopRow++) {
                    int[] loc = FindGuardPattern(matrix, previousRowLoc[0], stopRow, width, false, pattern, counters);
                    // a found pattern is only considered to belong to the same barcode if the start and end positions
                    // don't differ too much. Pattern drift should be not bigger than two for consecutive rows. With
                    // a higher number of skipped rows drift could be larger. To keep it simple for now, we allow a slightly
                    // larger drift and don't check for skipped rows.
                    if (loc != null &&
                        Math.Abs(previousRowLoc[0] - loc[0]) < MAX_PATTERN_DRIFT &&
                        Math.Abs(previousRowLoc[1] - loc[1]) < MAX_PATTERN_DRIFT) {
                        previousRowLoc = loc;
                        skippedRowCount = 0;
                    } else {
                        if (skippedRowCount > SKIPPED_ROW_COUNT_MAX) {
                            break;
                        } else {
                            skippedRowCount++;
                        }
                    }
                }
                stopRow -= skippedRowCount + 1;
                result[2] = new ResultPoint(previousRowLoc[0], stopRow);
                result[3] = new ResultPoint(previousRowLoc[1], stopRow);
            }
            if (stopRow - startRow < BARCODE_MIN_HEIGHT) {
                for (int i = 0; i < result.Length; i++) {
                    result[i] = null;
                }
            }
            return result;
        }

        // TODO use a lambda to do the counter set in-place?
        //private static readonly Converter<int, int> ConvertAllToZero = new Converter<int, int>(input => {return 0;});

        /// <summary>
        /// Finds the guard pattern.  Uses System.Linq.Enumerable.Repeat to fill in counters.  This might be a performance issue?
        /// </summary>
        /// <returns>start/end horizontal offset of guard pattern, as an array of two ints.</returns>
        /// <param name="matrix">matrix row of black/white values to search</param>
        /// <param name="column">column x position to start search.</param>
        /// <param name="row">row y position to start search.</param>
        /// <param name="width">width the number of pixels to search on this row.</param>
        /// <param name="whiteFirst">If set to <c>true</c> search the white patterns first.</param>
        /// <param name="pattern">pattern of counts of number of black and white pixels that are being searched for as a pattern.</param>
        /// <param name="counters">counters array of counters, as long as pattern, to re-use .</param>
        private static int[] FindGuardPattern(
            BitMatrix matrix,
            int column,
            int row,
            int width,
            bool whiteFirst,
            int[] pattern,
            int[] counters) 
        {

            counters = Enumerable.Repeat(0, counters.Length).ToArray(); // Clear out counters. (Java.Fill equiv)
            //Array.ConvertAll(counters, ConvertAllToZero);
            int patternLength = pattern.Length;
            bool isWhite = whiteFirst;
            int patternStart = column;
            int pixelDrift = 0;
            
            // if there are black pixels left of the current pixel shift to the left, but only for MAX_PIXEL_DRIFT pixels 
            while (matrix[patternStart, row] && patternStart > 0 && pixelDrift++ < MAX_PIXEL_DRIFT) {
                patternStart--;
            }
            int x = patternStart;
            int counterPosition = 0;
            for (; x < width; x++) {
                bool pixel = matrix[x, row];
                if (pixel ^ isWhite) {
                    counters[counterPosition]++;
                } else {
                    if (counterPosition == patternLength - 1) {
                        if (PatternMatchVariance(counters, pattern, MAX_INDIVIDUAL_VARIANCE) < MAX_AVG_VARIANCE) {
                            return new int[] {patternStart, x};
                        }
                        patternStart += counters[0] + counters[1];
                        Array.Copy(counters, 2, counters, 0, patternLength - 2);
                        counters[patternLength - 2] = 0;
                        counters[patternLength - 1] = 0;
                        counterPosition--;
                    } else {
                        counterPosition++;
                    }
                    counters[counterPosition] = 1;
                    isWhite = !isWhite;
                }
            }
            if (counterPosition == patternLength - 1) {
                if (PatternMatchVariance(counters, pattern, MAX_INDIVIDUAL_VARIANCE) < MAX_AVG_VARIANCE) {
                    return new int[] {patternStart, x - 1};
                }
            }
            return null;
        }
       
        /// <summary>
        /// Determines how closely a set of observed counts of runs of black/white.
        /// values matches a given target pattern. This is reported as the ratio of
        /// the total variance from the expected pattern proportions across all
        /// pattern elements, to the length of the pattern.
        /// </summary>
        /// <returns>
        /// ratio of total variance between counters and pattern compared to
        /// total pattern size, where the ratio has been multiplied by 256.
        /// So, 0 means no variance (perfect match); 256 means the total
        /// variance between counters and patterns equals the pattern length,
        /// higher values mean even more variance
        /// </returns>
        /// <param name="counters">observed counters.</param>
        /// <param name="pattern">expected pattern.</param>
        /// <param name="maxIndividualVariance">The most any counter can differ before we give up.</param>
        private static int PatternMatchVariance(int[] counters, int[] pattern, int maxIndividualVariance) {
            int numCounters = counters.Length;
            int total = 0;
            int patternLength = 0;
            for (int i = 0; i < numCounters; i++) {
                total += counters[i];
                patternLength += pattern[i];
            }
            if (total < patternLength) {
                // If we don't even have one pixel per unit of bar width, assume this
                // is too small to reliably match, so fail:
                return int.MaxValue;
            }
            // We're going to fake floating-point math in integers. We just need to use more bits.
            // Scale up patternLength so that intermediate values below like scaledCounter will have
            // more "significant digits".
            int unitBarWidth = (total << INTEGER_MATH_SHIFT) / patternLength;
            maxIndividualVariance = (maxIndividualVariance * unitBarWidth) >> INTEGER_MATH_SHIFT;
            
            int totalVariance = 0;
            for (int x = 0; x < numCounters; x++) {
                int counter = counters[x] << INTEGER_MATH_SHIFT;
                int scaledPattern = pattern[x] * unitBarWidth;
                int variance = counter > scaledPattern ? counter - scaledPattern : scaledPattern - counter;
                if (variance > maxIndividualVariance) {
                    return int.MaxValue;
                }
                totalVariance += variance;
            }
            return totalVariance / total;
        }
    }
}