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Java example source code file (MnistImageFile.java)

This example Java source code file (MnistImageFile.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

ioexception, mnistdbfile, mnistimagefile, override, string

The MnistImageFile.java Java example source code

/*
 *
 *  * Copyright 2015 Skymind,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 org.deeplearning4j.datasets.mnist;


import java.io.FileNotFoundException;
import java.io.IOException;


/**
 * 
 * MNIST database image file. Contains additional header information for the
 * number of rows and columns per each entry.
 * 
 */
public class MnistImageFile extends MnistDbFile {
    private int rows;
    private int cols;

    /**
     * Creates new MNIST database image file ready for reading.
     * 
     * @param name
     *            the system-dependent filename
     * @param mode
     *            the access mode
     * @throws IOException
     * @throws FileNotFoundException
     */
    public MnistImageFile(String name, String mode) throws  IOException {
        super(name, mode);

        // read header information
        rows = readInt();
        cols = readInt();
    }

    /**
     * Reads the image at the current position.
     * 
     * @return matrix representing the image
     * @throws IOException
     */
    public int[][] readImage() throws IOException {
        int[][] dat = new int[getRows()][getCols()];
        for (int i = 0; i < getCols(); i++) {
            for (int j = 0; j < getRows(); j++) {
                dat[i][j] = readUnsignedByte();
            }
        }
        return dat;
    }

    /** Read the specified number of images from the current position, to a byte[nImages][rows*cols]
     * Note that MNIST data set is stored as unsigned bytes; this method returns signed bytes without conversion
     * (i.e., same bits, but requires conversion before use)
     * @param nImages Number of images
     */
    public byte[][] readImagesUnsafe(int nImages) throws IOException{
        byte[][] out = new byte[nImages][0];
        for( int i=0; i<nImages; i++){
            out[i] = new byte[rows*cols];
            read(out[i]);
        }
        return out;
    }

    /**
     * Move the cursor to the next image.
     * 
     * @throws IOException
     */
    public void nextImage() throws IOException {
        super.next();
    }

    /**
     * Move the cursor to the previous image.
     * 
     * @throws IOException
     */
    public void prevImage() throws IOException {
        super.prev();
    }

    @Override
    protected int getMagicNumber() {
        return 2051;
    }

    /**
     * Number of rows per image.
     * 
     * @return int
     */
    public int getRows() {
        return rows;
    }

    /**
     * Number of columns per image.
     * 
     * @return int
     */
    public int getCols() {
        return cols;
    }

    @Override
    public int getEntryLength() {
        return cols * rows;
    }

    @Override
    public int getHeaderSize() {
        return super.getHeaderSize() + 8; // to more integers - rows and columns
    }
}

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