tesseract  5.0.0-alpha-619-ge9db
dppoint.h
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1 /**********************************************************************
2  * File: dppoint.h
3  * Description: Simple generic dynamic programming class.
4  * Author: Ray Smith
5  * Created: Wed Mar 25 18:57:01 PDT 2009
6  *
7  * (C) Copyright 2009, Google Inc.
8  ** Licensed under the Apache License, Version 2.0 (the "License");
9  ** you may not use this file except in compliance with the License.
10  ** You may obtain a copy of the License at
11  ** http://www.apache.org/licenses/LICENSE-2.0
12  ** Unless required by applicable law or agreed to in writing, software
13  ** distributed under the License is distributed on an "AS IS" BASIS,
14  ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15  ** See the License for the specific language governing permissions and
16  ** limitations under the License.
17  *
18  **********************************************************************/
19 
20 #ifndef TESSERACT_CCSTRUCT_DPPOINT_H_
21 #define TESSERACT_CCSTRUCT_DPPOINT_H_
22 
23 #include <cstdint>
24 
25 namespace tesseract {
26 
27 // A simple class to provide a dynamic programming solution to a class of
28 // 1st-order problems in which the cost is dependent only on the current
29 // step and the best cost to that step, with a possible special case
30 // of using the variance of the steps, and only the top choice is required.
31 // Useful for problems such as finding the optimal cut points in a fixed-pitch
32 // (vertical or horizontal) situation.
33 // Skeletal Example:
34 // DPPoint* array = new DPPoint[width];
35 // for (int i = 0; i < width; i++) {
36 // array[i].AddLocalCost(cost_at_i)
37 // }
38 // DPPoint* best_end = DPPoint::Solve(..., array);
39 // while (best_end != nullptr) {
40 // int cut_index = best_end - array;
41 // best_end = best_end->best_prev();
42 // }
43 // delete [] array;
44 class DPPoint {
45  public:
46  // The cost function evaluates the total cost at this (excluding this's
47  // local_cost) and if it beats this's total_cost, then
48  // replace the appropriate values in this.
49  using CostFunc = int64_t (DPPoint::*)(const DPPoint*);
50 
51  DPPoint()
52  : local_cost_(0),
53  total_cost_(INT32_MAX),
54  total_steps_(1),
55  best_prev_(nullptr),
56  n_(0),
57  sig_x_(0),
58  sig_xsq_(0) {}
59 
60  // Solve the dynamic programming problem for the given array of points, with
61  // the given size and cost function.
62  // Steps backwards are limited to being between min_step and max_step
63  // inclusive.
64  // The return value is the tail of the best path.
65  static DPPoint* Solve(int min_step, int max_step, bool debug,
66  CostFunc cost_func, int size, DPPoint* points);
67 
68  // A CostFunc that takes the variance of step into account in the cost.
69  int64_t CostWithVariance(const DPPoint* prev);
70 
71  // Accessors.
72  int total_cost() const {
73  return total_cost_;
74  }
75  int Pathlength() const {
76  return total_steps_;
77  }
78  const DPPoint* best_prev() const {
79  return best_prev_;
80  }
81  void AddLocalCost(int new_cost) {
82  local_cost_ += new_cost;
83  }
84 
85  private:
86  // Code common to different cost functions.
87 
88  // Update the other members if the cost is lower.
89  void UpdateIfBetter(int64_t cost, int32_t steps, const DPPoint* prev,
90  int32_t n, int32_t sig_x, int64_t sig_xsq);
91 
92  int32_t local_cost_; // Cost of this point on its own.
93  int32_t total_cost_; // Sum of all costs in best path to here.
94  // During cost calculations local_cost is excluded.
95  int32_t total_steps_; // Number of steps in best path to here.
96  const DPPoint* best_prev_; // Pointer to prev point in best path from here.
97  // Information for computing the variance part of the cost.
98  int32_t n_; // Number of steps in best path to here for variance.
99  int32_t sig_x_; // Sum of step sizes for computing variance.
100  int64_t sig_xsq_; // Sum of squares of steps for computing variance.
101 };
102 
103 } // namespace tesseract.
104 
105 #endif // TESSERACT_CCSTRUCT_DPPOINT_H_
tesseract::DPPoint::DPPoint
DPPoint()
Definition: dppoint.h:82
tesseract::DPPoint::AddLocalCost
void AddLocalCost(int new_cost)
Definition: dppoint.h:112
tesseract::DPPoint
Definition: dppoint.h:59
tesseract::DPPoint::CostWithVariance
int64_t CostWithVariance(const DPPoint *prev)
Definition: dppoint.cpp:85
tesseract::DPPoint::Solve
static DPPoint * Solve(int min_step, int max_step, bool debug, CostFunc cost_func, int size, DPPoint *points)
Definition: dppoint.cpp:47
tesseract::DPPoint::CostFunc
int64_t(DPPoint::*)(const DPPoint *) CostFunc
Definition: dppoint.h:80
tesseract
Definition: baseapi.h:65
tesseract::DPPoint::best_prev
const DPPoint * best_prev() const
Definition: dppoint.h:109
tesseract::DPPoint::Pathlength
int Pathlength() const
Definition: dppoint.h:106
tesseract::DPPoint::total_cost
int total_cost() const
Definition: dppoint.h:103