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);
    }
}