src/main/java/org/apache/pdfbox/jbig2/image/ParameterizedFilter.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.pdfbox.jbig2.image;

import org.apache.pdfbox.jbig2.util.Utils;

class ParameterizedFilter {
  public ParameterizedFilter(final Filter f, final double scale) {
    filter = f;
    /*
     * find scale of filter in a space (source space) when minifying, ascale=1/scale, but when
     * magnifying, ascale=1
     */
    this.scale = f.blur * Math.max(1., 1. / scale);

    /*
     * find support radius of scaled filter if ax.supp and ay.supp are both <=.5 then we've got
     * point sampling. Point sampling is essentially a special filter whose width is fixed at one
     * source pixel.
     */
    support = Math.max(.5, this.scale * f.support);
    width = (int) Math.ceil(2. * support);
  }

  public ParameterizedFilter(final Filter f, final double scale, final double support, final int width) {
    filter = f;
    this.scale = scale;
    this.support = support;
    this.width = width;
  }

  final Filter filter;

  /* filter scale (spacing between centers in a space) */
  final double scale;

  /* scaled filter support radius */
  final double support;

  /* filter width: max number of nonzero samples */
  final int width;

  public double eval(double center, int i) {
    return filter.fWindowed((i + .5 - center) / scale);
  }

  public int minIndex(double center) {
    return Utils.floor(center - support);
  }

  public int maxIndex(double center) {
    return Utils.ceil(center + support);
  }
}