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Java library for reading and writing FITS files. FITS, the Flexible Image Transport System, is the format commonly used in the archiving and transport of astronomical data.
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package nom.tam.image.compression.tile.mask;

/*
 * #%L
 * nom.tam FITS library
 * %%
 * Copyright (C) 1996 - 2024 nom-tam-fits
 * %%
 * This is free and unencumbered software released into the public domain.
 *
 * Anyone is free to copy, modify, publish, use, compile, sell, or
 * distribute this software, either in source code form or as a compiled
 * binary, for any purpose, commercial or non-commercial, and by any
 * means.
 *
 * In jurisdictions that recognize copyright laws, the author or authors
 * of this software dedicate any and all copyright interest in the
 * software to the public domain. We make this dedication for the benefit
 * of the public at large and to the detriment of our heirs and
 * successors. We intend this dedication to be an overt act of
 * relinquishment in perpetuity of all present and future rights to this
 * software under copyright law.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 * #L%
 */

import java.nio.ByteBuffer;

import nom.tam.fits.compression.algorithm.api.ICompressorControl;
import nom.tam.image.tile.operation.buffer.TileBuffer;

/**
 * (for internal use) Base support for blank (null) in
 * compressed images. In regular images specific values (such as
 * {@link Double#NaN} or a specific integer value) may be used to indicate
 * missing data. However, because of e.g. quantization or lossy compression,
 * these specific values may not be recovered exactly when compressing /
 * decompressing images. Hence, there is a need to demark null
 * values differently in copmressed images. This class provides support for that
 * purpose.
 */
public class AbstractNullPixelMask {

    private static final byte[] EMPTY_BYTE_ARRAY = new byte[0];

    /** Byte value signifying invalid / null data */
    protected static final byte NULL_INDICATOR = (byte) 1;

    private final TileBuffer tileBuffer;

    private final int tileIndex;

    private final long nullValue;

    private ByteBuffer mask;

    private final ICompressorControl compressorControl;

    /**
     * Creates a new pixel mask got a given image tile and designated null
     * value.
     * 
     * @param tileBuffer
     *            the buffer containing the tile data
     * @param tileIndex
     *            the tile index
     * @param nullValue
     *            the integer value representing null or invalid
     *            data
     * @param compressorControl
     *            The class managing the compression
     * @throws IllegalStateException
     *             if the compressorControl argument is null
     */
    protected AbstractNullPixelMask(TileBuffer tileBuffer, int tileIndex, long nullValue, ICompressorControl compressorControl) throws IllegalStateException {
        this.tileBuffer = tileBuffer;
        this.tileIndex = tileIndex;
        this.nullValue = nullValue;
        this.compressorControl = compressorControl;
        if (this.compressorControl == null) {
            throw new IllegalStateException("Compression algorithm for the null pixel mask not available");
        }
    }

    /**
     * Returns a byte array containing the mask
     * 
     * @return the byte array containing the pixel mask for the tile.
     * @deprecated (for internal use) Visibility may be reduced to
     *             package level in the future.
     */
    public byte[] getMaskBytes() {
        if (mask == null) {
            return EMPTY_BYTE_ARRAY;
        }
        int size = mask.position();
        byte[] result = new byte[size];
        mask.rewind();
        mask.get(result);
        return result;
    }

    /**
     * Sets data for a new mask as a flattened buffer of data.
     * 
     * @param mask
     *            the buffer containing the mask data in flattened format.
     */
    public void setMask(ByteBuffer mask) {
        this.mask = mask;
    }

    /**
     * Returns the object that manages the compression, and which therefore
     * handles the masking
     * 
     * @return the object that manages the compression.
     */
    protected ICompressorControl getCompressorControl() {
        return compressorControl;
    }

    /**
     * Returns the mask data as a buffer in flattened format.
     * 
     * @return the buffer containing the mask data in flattened format.
     */
    protected ByteBuffer getMask() {
        return mask;
    }

    /**
     * Returns the value that represents a null or an undefined
     * data point.
     * 
     * @return the value that demarks an undefined datum.
     */
    protected long getNullValue() {
        return nullValue;
    }

    /**
     * Returns the buffer that holds data for an image tile.
     * 
     * @return the buffer that holds data for a single image tile.
     */
    protected TileBuffer getTileBuffer() {
        return tileBuffer;
    }

    /**
     * Return the tile index for the image tile that is processed.
     * 
     * @return the image tile index
     */
    protected int getTileIndex() {
        return tileIndex;
    }

    /**
     * Creates an internal buffer for holding the mask data, for the specified
     * number of points.
     * 
     * @param remaining
     *            the number of points the mask should accomodate.
     * @return the internal buffer that may store the mask data for the
     *         specified number of data points.
     */
    protected ByteBuffer initializedMask(int remaining) {
        if (mask == null) {
            mask = ByteBuffer.allocate(remaining);
        }
        return mask;
    }
}