content: /*
   * Copyright (C) 2011 Google Inc.
   * 
   * 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.googlecode.leptonica.android;
  
  /**
   * Image rotation and skew detection methods.
   *
   * @author alanv@google.com (Alan Viverette)
   */
  public class Skew {
      static {
          System.loadLibrary("lept");
      }
  
      // Text alignment defaults
      
      /** Default range for sweep, will detect rotation of + or - 30 degrees. */
      public final static float SWEEP_RANGE = 30.0f;
  
      /** Default sweep delta, reasonably accurate within 0.05 degrees. */
      public final static float SWEEP_DELTA = 5.0f;
  
      /** Default sweep reduction, one-eighth the size of the original image. */
      public final static int SWEEP_REDUCTION = 8;
  
      /** Default sweep reduction, one-fourth the size of the original image. */
      public final static int SEARCH_REDUCTION = 4;
  
      /** Default search minimum delta, reasonably accurate within 0.05 degrees. */
      public final static float SEARCH_MIN_DELTA = 0.01f;
  
      /** 
       * Finds and returns the skew angle using default parameters.
       * 
       * @param pixs Input pix (1 bpp).
       * @return the detected skew angle, or 0.0 on failure
       */
      public static float findSkew(Pix pixs) {
          return findSkew(pixs, SWEEP_RANGE, SWEEP_DELTA, SWEEP_REDUCTION, SEARCH_REDUCTION,
                  SEARCH_MIN_DELTA);
      }
  
      /**
       * Finds and returns the skew angle, doing first a sweep through a set of
       * equal angles, and then doing a binary search until convergence.
       * <p>
       * Notes:
       * <ol>
       * <li>In computing the differential line sum variance score, we sum the
       * result over scanlines, but we always skip:
       * <ul>
       * <li>at least one scanline
       * <li>not more than 10% of the image height
       * <li>not more than 5% of the image width
       * </ul>
       * </ol>
       *
       * @param pixs Input pix (1 bpp).
       * @param sweepRange Half the full search range, assumed about 0; in
       *            degrees.
       * @param sweepDelta Angle increment of sweep; in degrees.
       * @param sweepReduction Sweep reduction factor = 1, 2, 4 or 8.
       * @param searchReduction Binary search reduction factor = 1, 2, 4 or 8; and
       *            must not exceed redsweep.
       * @param searchMinDelta Minimum binary search increment angle; in degrees.
       * @return the detected skew angle, or 0.0 on failure
       */
      public static float findSkew(Pix pixs, float sweepRange, float sweepDelta, int sweepReduction,
              int searchReduction, float searchMinDelta) {
          if (pixs == null)
              throw new IllegalArgumentException("Source pix must be non-null");
  
          return nativeFindSkew(pixs.mNativePix, sweepRange, sweepDelta, sweepReduction,
                  searchReduction, searchMinDelta);
      }
  
      // ***************
      // * NATIVE CODE *
      // ***************
  
      private static native float nativeFindSkew(int nativePix, float sweepRange, float sweepDelta,
              int sweepReduction, int searchReduction, float searchMinDelta);
  
  }
  