src/main/java/org/apache/pdfbox/jbig2/image/Weighttab.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 static java.lang.Math.max;
import static java.lang.Math.min;

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

final class Weighttab
{
    final int weights[]; /* weight[i] goes with pixel at i0+i */
    final int i0, i1; /* range of samples is [i0..i1-1] */

    /*
     * make_weighttab: sample the continuous filter, scaled by ap.scale and positioned at continuous source coordinate
     * cen, for source coordinates in the range [0..len-1], writing the weights into wtab. Scale the weights so they sum
     * to WEIGHTONE, and trim leading and trailing zeros if trimzeros!=0. b is the dest coordinate (for diagnostics).
     */
    public Weighttab(ParameterizedFilter pf, int weightOne, final double center, int a0,
            final int a1, final boolean trimzeros)
    {
        // find the source coord range of this positioned filter: [i0..i1-1] and clamp to input range
        int i0 = max(pf.minIndex(center), a0);
        int i1 = min(pf.maxIndex(center), a1);

        // find scale factor sc to normalize the filter
        double den = 0;
        for (int i = i0; i <= i1; i++)
            den += pf.eval(center, i);

        // set sc so that sum of sc*func() is approximately WEIGHTONE
        final double scale = den == 0. ? weightOne : weightOne / den;

        // find range of non-zero samples
        if (trimzeros)
        {
            boolean stillzero = trimzeros;
            int lastnonzero = 0;
            for (int i = i0; i <= i1; i++)
            {
                /* evaluate the filter function at p */
                final double tr = Utils.clamp(scale * pf.eval(center, i), Short.MIN_VALUE,
                        Short.MAX_VALUE);

                final int t = (int) Math.floor(tr + .5);
                if (stillzero && t == 0)
                    i0++; /* find first nonzero */
                else
                {
                    stillzero = false;
                    if (t != 0)
                        lastnonzero = i; /* find last nonzero */
                }
            }

            i1 = max(lastnonzero, i0);
        }

        // initialize weight table of appropriate length
        weights = new int[i1 - i0 + 1];

        // compute the discrete, sampled filter coefficients
        int sum = 0;
        for (int idx = 0, i = i0; i <= i1; i++)
        {
            /* evaluate the filter function at p */
            final double tr = Utils.clamp(scale * pf.eval(center, i), Short.MIN_VALUE,
                    Short.MAX_VALUE);

            final int t = (int) Math.floor(tr + .5);
            weights[idx++] = t; /* add weight to table */
            sum += t;
        }

        if (sum == 0)
        {
            i1 = i0;
            weights[0] = weightOne;
        }
        else if (sum != weightOne)
        {
            /*
             * Fudge the center slightly to make sum=WEIGHTONE exactly. Is this the best way to normalize a discretely
             * sampled continuous filter?
             */
            int i = (int) (center + .5);
            if (i >= i1)
                i = i1 - 1;
            if (i < i0)
                i = i0;
            final int t = weightOne - sum;
            if (Resizer.debug)
                System.out.printf("[%d]+=%d ", i, t);
            weights[i - i0] += t; /* fudge center sample */
        }

        this.i0 = i0 - a0;
        this.i1 = i1 - a0;

        if (Resizer.debug)
        {
            System.out.printf("\t");
            for (int idx = 0, i = i0; i < i1; i++, idx++)
                System.out.printf("%5d ", weights[idx]);
            System.out.printf("\n");
        }
    }

}