src/test/java/org/apache/commons/imaging/formats/jpeg/decoder/DctTest.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.commons.imaging.formats.jpeg.decoder;

import junit.framework.TestCase;

public class DctTest extends TestCase
{
    public void testVectors() throws Exception
    {
        float[] originalData = new float[8];
        for (int i = 0; i < 8; i++)
        {
            originalData[i] = i;
        }

        float[] transformed = REFERENCE_forwardDCT(originalData);
        float[] reversed = REFERENCE_inverseDCT(transformed);
        for (int i = 0; i < 8; i++)
        {
            assertEquals("Reference transforms broken, at x=" + i, originalData[i], reversed[i], 0.001);
        }

        float[] data = originalData.clone();
        Dct.forwardDCT8(data);
        Dct.scaleQuantizationVector(data);
        for (int i = 0; i < 8; i++)
        {
            assertEquals("Forward transform broken, at x=" + i, data[i], transformed[i], 0.001);
        }
        
        Dct.scaleDequantizationVector(data);
        Dct.inverseDCT8(data);
        for (int i = 0; i < 8; i++)
        {
            assertEquals("Inverse transform broken, at x=" + i, data[i], originalData[i], 0.001);
        }
    }

    public void testMatrices() throws Exception
    {
        float[] originalData = new float[8 * 8];
        float[][] originalData8x8 = new float[8][8];
        for (int y = 0; y < 8; y++)
        {
            for (int x = 0; x < 8; x++)
            {
                float value = 8 * y + x;
                originalData8x8[y][x] = value;
                originalData[8 * y + x] = value;
            }
        }

        float[][] transformed8x8 = REFERENCE_forwardDCT(originalData8x8);
        float[][] reversed8x8 = REFERENCE_inverseDCT(transformed8x8);
        for (int y = 0; y < 8; y++)
        {
            for (int x = 0; x < 8; x++)
            {
                assertEquals("Reference transforms broken, at x=" + x + ",y=" + y, originalData8x8[y][x], reversed8x8[y][x], 0.001);
            }
        }

        float[] data = originalData.clone();
        Dct.forwardDCT8x8(data);
        Dct.scaleQuantizationMatrix(data);
        for (int y = 0; y < 8; y++)
        {
            for (int x = 0; x < 8; x++)
            {
                assertEquals("Forward transform broken, at x=" + x + ",y=" + y, transformed8x8[y][x], data[8 * y + x], 0.001);
            }
        }

        Dct.scaleDequantizationMatrix(data);
        Dct.inverseDCT8x8(data);
        for (int y = 0; y < 8; y++)
        {
            for (int x = 0; x < 8; x++)
            {
                assertEquals("Inverse transform broken, at x=" + x + ",y=" + y, originalData8x8[y][x], data[8 * y + x], 0.001);
            }
        }
    }


    private static float[][] REFERENCE_inverseDCT(float[][] matrix)
    {
        float[][] ret = new float[8][8];
        for (int y = 0; y < 8; y++)
        {
            for (int x = 0; x < 8; x++)
            {
                float sum = 0;
                for (int u = 0; u < 8; u++)
                {
                    for (int v = 0; v < 8; v++)
                    {
                        float cu = (u == 0) ? ((float) (1.0 / Math.sqrt(2))) : 1;
                        float cv = (v == 0) ? ((float) (1.0 / Math.sqrt(2))) : 1;
                        sum += cu * cv * matrix[v][u] *
                                Math.cos((2 * x + 1) * u * Math.PI / 16) *
                                Math.cos((2 * y + 1) * v * Math.PI / 16);
                    }
                }
                ret[y][x] = 0.25f * sum;
            }
        }
        return ret;
    }

    private static float[] REFERENCE_inverseDCT(float[] vector)
    {
        float[] ret = new float[8];
        for (int x = 0; x < 8; x++)
        {
            float sum = 0;
            for (int u = 0; u < 8; u++)
            {
                float cu = (u == 0) ? ((float) (1.0 / Math.sqrt(2))) : 1;
                sum += cu * vector[u] *
                        Math.cos((2 * x + 1) * u * Math.PI / 16);
            }
            ret[x] = 0.5f * sum;
        }
        return ret;
    }

    private static float[][] REFERENCE_forwardDCT(float[][] matrix)
    {
        float[][] ret = new float[8][8];
        for (int u = 0; u < 8; u++)
        {
            for (int v = 0; v < 8; v++)
            {
                float sum = 0;
                float cu = (u == 0) ? ((float) (1.0 / Math.sqrt(2))) : 1;
                float cv = (v == 0) ? ((float) (1.0 / Math.sqrt(2))) : 1;
                for (int x = 0; x < 8; x++)
                {
                    for (int y = 0; y < 8; y++)
                    {
                        sum += matrix[y][x] *
                                Math.cos((2 * x + 1) * u * Math.PI / 16) *
                                Math.cos((2 * y + 1) * v * Math.PI / 16);
                    }
                }
                ret[v][u] = 0.25f * cu * cv * sum;
            }
        }
        return ret;
    }

    private static float[] REFERENCE_forwardDCT(float[] vector)
    {
        float[] ret = new float[8];
        for (int u = 0; u < 8; u++)
        {
            float sum = 0;
            float cu = (u == 0) ? ((float) (1.0 / Math.sqrt(2))) : 1;
            for (int x = 0; x < 8; x++)
            {
                sum += vector[x] *
                        Math.cos((2 * x + 1) * u * Math.PI / 16);
            }
            ret[u] = 0.5f * cu * sum;
        }
        return ret;
    }
}