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/*************************************************************************
 *
 * ADOBE CONFIDENTIAL
 * __________________
 *
 *  Copyright 2012 Adobe Systems Incorporated
 *  All Rights Reserved.
 *
 * NOTICE:  All information contained herein is, and remains
 * the property of Adobe Systems Incorporated and its suppliers,
 * if any.  The intellectual and technical concepts contained
 * herein are proprietary to Adobe Systems Incorporated and its
 * suppliers and are protected by trade secret or copyright law.
 * Dissemination of this information or reproduction of this material
 * is strictly forbidden unless prior written permission is obtained
 * from Adobe Systems Incorporated.
 **************************************************************************/
package com.day.image;

import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;
import java.awt.image.ColorModel;
import java.awt.image.IndexColorModel;
import java.awt.image.Raster;
import java.awt.image.WritableRaster;

/**
 * The DitherOp provides the dithering capability for reducing
 * colors of an image to any number of colors. The real number of colors at the
 * end of color reduction depends on the color profile of the image under
 * reduction.
 * 

 * Currently the following two dithering algorithm's are supported :
 * 

 * 
Simple reduction by reducing the bit width of the color components
 * 
Reduction by reducing the bit width and doing some rudimentary error
 *     correction on neighbouring pixels.
 * 
 *
 * @see Implementation of Image
 * 	Dithering/Color Reduction
 *
 * @version $Revision$, $Date$
 * @author fmeschbe, based on CQ2's rgba2/rgbacolor.c color reduction
 * @since coati
 * @audience wad
 */
public class DitherOp extends AbstractBufferedImageOp {

    /**
     * Indicate the use of the simple bit width color reduction algorithm
     * with no further dithering effects.
     */
    public static final DitherAlgorithm DITHER_NONE =
	new DitherSimple();

    /**
     * Indicate the use of the simple bit width color reduction algorithm
     * plus using the simple error correction algorithm.
     */
    public static final DitherAlgorithm DITHER_SIMPLE_ERROR_CORRECTION  =
	new DitherErrorCorrection();

    /** The maximum number of colors to accept after reduction. */
    private final int nCol;

    /**
     * The Color to use for transparency. It is guaranteed, that this color is
     * part of the colors remaining in the image.
     */
    private final Color transparency;

    /**
     * The Color to use for the background. It is guaranteed, that this color is
     * part of the colors remaining in the image.
     */
    private final Color bgcolor;

    /** The algorithm used for color reduction. */
    private final DitherAlgorithm algorithm;

    /**
     * Creates a new DitherOp instance to reduce colors of an
     * image to the given number of colors.
     *
     * @param nCol The maximum number of colors to reduce the image to. This
     * 		must be higher than 2.
     * @param transparency The Color of the color to be considered
     * 		as transparent. This will be one of the nCol colors if not
     * 		null.
     * @param bgcolor The Color of the color to be considered
     * 		as the background. This will be one of the nCol colors if
     * 		not null.
     * @param algorithm The dithering algorithm to be used.
     * @param hints The RenderingHints for the filter operation. This parameter
     * 		may be null and is not currently used.
     *
     * @throws NullPointerException if algorithm is null.
     * @throws IllegalArgumentException if nCol is less than 2.
     */
    public DitherOp(int nCol, Color transparency, Color bgcolor,
	DitherAlgorithm algorithm, RenderingHints hints) {

	// init base class
	super(hints);

	// check algorithm
	if (algorithm == null) {
	    throw new NullPointerException("algorithm");
	}

	// Check nCol
	if (nCol < 2) {
	    throw new IllegalArgumentException("nCol < 2");
	}

	this.nCol = nCol;
	this.transparency = transparency;
	this.bgcolor = bgcolor;
	this.algorithm = algorithm;
    }

    /**
     * Converts the source image to an image with IndexColorModel and with
     * a maximal number of colors. If the source image already has an IndexColorModel and
     * the map size of the that color model instance
     * (src.getColorModel().getMapSize()) is less than or equal to
     * the number of colors desired, the source image is returned. Else a new
     * image is returned.
     *
     * @param src The source image to convert to the IndexColorModel.
     * @param nCol The maximum number of colors to reduce the image to. This
     * 		must be higher than 2.
     * @param transparency The Color of the color to be considered
     * 		as transparent. This will be one of the nCol colors if not
     * 		null.
     * @param bgcolor The Color of the color to be considered
     * 		as the background. This will be one of the nCol colors if
     * 		not null.
     * @param hints The RenderingHints for the filter operation. This parameter
     * 		may be null and is not currently used.
     *
     * @return An image with the IndexColorModel color model. If
     * 		the source image already has the IndexColorModel
     * 		and the number of colors are less than or equal to
     * 		nCol the source image is returned else a new
     * 		image according to the parameters is returned.
     *
     * @throws NullPointerException if the source image is null.
     * @throws NullPointerException if algorithm is null.
     * @throws IllegalArgumentException if nCol is less than 2.
     */
    public static BufferedImage convertToIndexed(BufferedImage src, int nCol,
	Color transparency, Color bgcolor, RenderingHints hints) {

	if (src == null) {
	    throw new NullPointerException("src image is null");
	}

	// Can't convolve an IndexColorModel.  Need to expand it
	ColorModel srcCM = src.getColorModel();
	if (srcCM instanceof IndexColorModel) {
	    IndexColorModel icm = (IndexColorModel) srcCM;

	    // if the index model has the max colors, return it
	    if (icm.getMapSize() <= nCol) {
		return src;
	    }

	    // else convert to RGBA and continue
	    src = icm.convertToIntDiscrete(src.getRaster(), true);
	}

        // make sure alpha is premultiplied as it is ignored later
        src = ImageSupport.coerceData(src, true);

	// special case for two-color output
	boolean doTransparency = transparency != null && nCol > 2;
	int transpOffset = doTransparency ? 1 : 0;

	// The instance used as a helper
	DitherOp dither = new DitherOp(nCol-transpOffset, transparency, bgcolor,
	    DITHER_NONE, hints);

	// the rasters we work on
	Raster srcRas = src.getRaster();

	// build the color tree for the source image
	dither.prepareSourceImage(src);
	OctTree tree = dither.buildColorTree(srcRas);

	// Dimensions of the layer
	int w = src.getWidth();
	int h = src.getHeight();

	// the colormap stuff
	dither.indexColorTree(tree, false);
	int size = tree.leafCount + transpOffset;
	byte[] cmap = tree.createColorMap(new byte[ size * 3 ]);
	int bits = 0;
	for (int ts=size; ts > 0; ts>>=1, bits++) {}

	// get the transparent color node
	int transparentIndex = size - 1;
	if (doTransparency) {
	    OctTreeNode node = tree.getNode(transparency.getRed(),
		transparency.getGreen(), transparency.getBlue());

	    // modify the index of the transparent color
	    node.nofcolors = transparentIndex;
	}

	// build the image
	IndexColorModel cm = new IndexColorModel(bits, size, cmap, 0, false,
                transparentIndex);
        WritableRaster dstRas = cm.createCompatibleWritableRaster(w, h);
	BufferedImage dst = new BufferedImage(cm, dstRas,
                cm.isAlphaPremultiplied(), null);

	// get the chunkbuffer - one image line
	int bands = srcRas.getNumBands();
	int[] srcChunk = new int[bands * w];
	int[] dstChunk = new int[w];  // dest raster assumed to have on band

	// convert the color values
	for (int y=0; y < h; y++) {
	    srcRas.getPixels(0, y, w, 1, srcChunk);
	    for (int x=srcChunk.length-bands, i=dstChunk.length-1; x >= 0;
		    x-=bands, i--) {
		if (srcChunk[x+3] == 0 && doTransparency) {
		    dstChunk[i] = transparentIndex;
		} else {
		    OctTreeNode node =
			tree.getNode(srcChunk[x], srcChunk[x+1], srcChunk[x+2]);
		    dstChunk[i] = node.nofcolors;
		}
	    }
	    dstRas.setPixels(0, y, w, 1, dstChunk);

	}

	return dst;
    }

    //---------- BufferedImageOp interface -------------------------------------

    /**
     * Performs the operation on a BufferedImage. This implementation only cares
     * to make the images compatible and calls the
     * {@link #doFilter(BufferedImage, BufferedImage)} to do the actual
     * filtering operation.
     * 

     * If the color models for the two images do not match, a color
     * conversion into the destination color model will be performed.
     * If the destination image is null,
     * a BufferedImage with an appropriate ColorModel will be created.
     * 

     * Note: The dest image might be clipped if it is not big enough to take
     * the complete resized image.
     * 

     * This method is overwritten to make sure the pixel data is premultiplied
     * with the alpha value to take the real alpha value into account.
     *
     * @param src The src image to be resized.
     * @param dst The dest image into which to place the resized image. This
     * 		may be null in which case a new image with the
     * 		correct size will be created.
     *
     * @return The newly created image (if dest was null) or dest
     * 		into which the resized src image has been drawn.
     *
     * @throws IllegalArgumentException if the dest image is the same as the
     * 		src image.
     * @throws NullPointerException if the src image is null.
     */
    public BufferedImage filter(BufferedImage src, BufferedImage dst) {

        // make sure alpha is premultiplied
        src = ImageSupport.coerceData(src, true);

        return super.filter(src, dst);
    }
    //---------- protected -----------------------------------------------------

    /**
     * Analize and reduce the number of colors of the given image. If the number
     * of colors in the image is less than required number, no image
     * manipulation is done and the source image is drawn into the destination
     * image.
     *
     * @param srcIm The BufferedImage to submit to color reduction.
     * @param dstIm The BufferedImage to use for the image with
     * 		at most the number of colors defined with the constructor.
     *
     * @throws NullPointerException if either srcIm or dstIm is null.
     */
    protected void doFilter(BufferedImage srcIm, BufferedImage dstIm) {

	// the rasters we work on
	Raster srcRas = srcIm.getRaster();
	WritableRaster dstRas = dstIm.getRaster();

	// build the color tree for the source image
	prepareSourceImage(srcIm);
	OctTree tree = buildColorTree(srcRas);

	// If we did not have node reduction, simply copy the image
	if (!tree.isReduced()) {
	    dstIm.getGraphics().drawImage(srcIm, 0, 0, null);
	}

	indexColorTree(tree, false);

	// replace old colors by new colors
	algorithm.dither(srcRas, dstRas, tree);
    }

    //---------- internal helper -----------------------------------------------

    private void prepareSourceImage(BufferedImage srcIm) {
	// Make all alpha values 0xff
	if (bgcolor != null) {
            Graphics2D g2 = srcIm.createGraphics();
            g2.setComposite(AlphaComposite.DstOver);
            Color col = (bgcolor.getAlpha() != 0)
		      ? new Color(bgcolor.getRGB()&0x00ffffff, true) // alpha=0
		      : bgcolor;
            g2.setColor(col);
            g2.fillRect(0, 0, srcIm.getWidth(), srcIm.getHeight());
	    g2.dispose();
        }

    }

    private OctTree buildColorTree(Raster srcRas) {

	// Dimensions of the layer
        int w = srcRas.getWidth();
        int h = srcRas.getHeight();
        int size = w * h;

	// get the chunkbuffer - one image line
	int bands = srcRas.getNumBands();
	int[] chunk = new int[bands * w];

	// Build the reduction tree from the pixels
	OctTree tree = new OctTree();
	for (int y=0; y < h; y++) {
	    srcRas.getPixels(0, y, w, 1, chunk);
	    for (int x=chunk.length-bands; x >= 0; x-=bands) {
		tree.insertNode(chunk[x], chunk[x+1], chunk[x+2], 1);
	    }

	    // Check if reduction is needed
	    while (tree.leafCount > nCol) {
		// reduce the tree
		tree.reduceNode();
	    }
	}

	// if we have a transparency color, insert with high weight
        if (transparency != null) {
	    tree.insertNode(transparency.getRed(), transparency.getGreen(),
		transparency.getBlue(), size);
        }

        // if we have a background color, insert with high weight
        if (bgcolor != null && !bgcolor.equals(transparency)) {
	    tree.insertNode(bgcolor.getRed(), bgcolor.getGreen(),
		bgcolor.getBlue(), size);
        }

	// Check for the last time now
	while (tree.leafCount > nCol) {
	    // reduce the tree
	    tree.reduceNode();
	}

	return tree;
    }

    private byte[] indexColorTree(OctTree tree, boolean createCMap) {

	// calculate color values and index tree
	tree.indexTree();

	// if we have transparent color, set alpha of its node to 0
	if (transparency != null) {
	    tree.getNode(transparency.getRed(), transparency.getGreen(),
		transparency.getBlue()).a = 0;
	}

	// optionally build the color map from the tree
	return (createCMap) ? tree.createColorMap(null) : null;
    }

    //---------- dither algorithms ---------------------------------------------

    public static interface DitherAlgorithm {
	public void dither(Raster src, WritableRaster dst, OctTree tree);
    }

    private static class DitherSimple implements DitherAlgorithm {
	public void dither(Raster src, WritableRaster dst, OctTree tree) {
	    // Dimensions of the layer
	    int w = src.getWidth();
	    int h = src.getHeight();

	    // get the chunkbuffer - one image line
	    int bands = src.getNumBands();
	    int[] chunk = new int[bands * w];

	    for (int y=0; y < h; y++) {
		src.getPixels(0, y, w, 1, chunk);
		for (int x=chunk.length-bands; x >= 0; x-=bands) {
		    OctTreeNode node =
			tree.getNode(chunk[x], chunk[x+1], chunk[x+2]);
		    chunk[x]   = node.r;
		    chunk[x+1] = node.g;
		    chunk[x+2] = node.b;
		    chunk[x+3] = node.a;
		}
		dst.setPixels(0, y, w, 1, chunk);

	    }
	}
    }

    private static class DitherErrorCorrection implements DitherAlgorithm {
	public void dither(Raster src, WritableRaster dst, OctTree tree) {
/*
	    // Dimensions of the layer
	    int w = src.getWidth();
	    int h = src.getHeight();

	    // get the chunkbuffer - one image line
	    int bands = src.getNumBands();
	    int[] chunk = new int[bands * w];

	    // if we have transparency, we have first to fill the alpha channel
	    if (transparency != Long.MAX_VALUE) {
		for (int i=0; i 255) rr = 255;
			    int gg = rgba.g + (eg*3/8); if (gg < 0) gg = 0; if (gg > 255) gg = 255;
			    int bb = rgba.b + (eb*3/8); if (bb < 0) bb = 0; if (bb > 255) bb = 255;
			    orgb[of+1] = orgb[of+1] & 0xff000000 + (rr << 16) + (gg << 8) + bb;
			}

			// pixel below
			if (y < h-1) {
			    rgba.setFromColor(orgb[of+w]);
			    int rr = rgba.r + (er*3/8); if (rr < 0) rr = 0; if (rr > 255) rr = 255;
			    int gg = rgba.g + (eg*3/8); if (gg < 0) gg = 0; if (gg > 255) gg = 255;
			    int bb = rgba.b + (eb*3/8); if (bb < 0) bb = 0; if (bb > 255) bb = 255;
			    orgb[of+w] = orgb[of+w] & 0xff000000 + (rr << 16) + (gg << 8) + bb;
			}

			// pixel below, right
			if ((x < w-1) && (y < h-1)){
			    rgba.setFromColor(orgb[of+w+1]);
			    int rr = rgba.r + (er/4); if (rr < 0) rr = 0; if (rr > 255) rr = 255;
			    int gg = rgba.g + (eg/4); if (gg < 0) gg = 0; if (gg > 255) gg = 255;
			    int bb = rgba.b + (eb/4); if (bb < 0) bb = 0; if (bb > 255) bb = 255;
			    orgb[of+w+1] = orgb[of+w+1] & 0xff000000 + (rr << 16) + (gg << 8) + bb;
			}

		    }
		}
	    }
*/
	}
    }

    //---------- internal classes ----------------------------------------------

    /**
     * The OctTreeNode class represents one node in the
     * OctTree.
     */
    private static final class OctTreeNode {

	/** The weighted red component */
	public int sr;

	/** The weighted green component */
	public int sg;

	/** The weighted blue component */
	public int sb;

	/** The unweighted red component, set by {@link #indexTree()}. */
	public int r;

	/** The unweighted green component, set by {@link #indexTree()}. */
	public int g;

	/** The unweighted blue component, set by {@link #indexTree()}. */
	public int b;

	/** The alpha value, opaque by default. */
	public int a = 255;

        /**
         * The list of children of this node. If this node is a leaf, there
         * are no children.
         */
        public OctTreeNode[] childs = new OctTreeNode[8];

        /**
         * The parent of this node. This is only used for tree reduction.
         */
        public OctTreeNode parent;

        /** Set to true if this node is a leaf node. */
        public boolean leaf;

        /**
         * The number of pixels bearing the color value represented by this
         * node, if this is a leaf node. Else this is not valid and/or set.
	 * 

	 * When building the color map this field is used to store the index
	 * number of the color in.
         */
        public int nofcolors;

        /** The level of the insertion point of this node. */
        public int depth;

	/**
	 * The next node in the color reduction lists ({@link OctTree#redtable}.
	 */
	public OctTreeNode next;

        /**
         * Create a node under the given parent. The parent is linked and the
         * depth is set based on the depth of the parent. If the parent is null
         * the depth set is 0 else it is one higher than the depth of the
         * parent.
         *
         * @param parent The parent under which this node will be located or
         *        null if this is a root or anchor node.
         */
        private OctTreeNode(OctTreeNode parent) {
            this.depth = (parent != null) ? parent.depth + 1 : 0;
            this.parent = parent;
            this.leaf = false;            // Of course we are not a leaf
	    this.next = null;
        }

        /**
         * Recurse down the tree, visiting all leaf nodes and calculating their
	 * real unweighted rgb color values.
         * 

         * This method is not intended to be used by the OctTree clients
	 * directly but is called by the {@link OctTree#indexTree} method.
         */
        public void indexTree() {

            if (leaf) {

                /**
                 * We divide the accumulated color value by the number
                 * of pixels. This may result in rounding errors, so
                 * we introduce the roundoff value to increase the accumulated
                 * color before division to do proper rounding up or down.
                 */

                // populate the palette, if we are a leaf.
                int roundoff = nofcolors >> 1;
		r = ((sr + roundoff) / nofcolors);
		g = ((sg + roundoff) / nofcolors);
		b = ((sb + roundoff) / nofcolors);

                // Note: Recursion stops here

            } else {

                // We are an inner node and have to recurse to our children
                for (int i=0; i<8; i++) {
                    if (childs[i] != null) {
			childs[i].indexTree();
		    }
                }

            }
        }

    }

    /**
     * The OctTree class provides the data structure to build
     * a tree of color values which is very easily traversed and simplifies
     * color reduction on a bit by bit basis.
     * 

     * NOTE: This class implements a specialization of the general octal tree.
     * 

     * Initially - before reduction - the tree has a fixed height of eight
     * where each node has 0 (only leafs) to 8 children and leafs are only
     * located at the bottom.
     * 

     * To reduce a node, the children, which must be leafs themselves, are
     * removed and the node reduced, is changed to a leaf node, effectively
     * reducing the height of the tree. To help identification of nodes to
     * reduce, each node carries a weight value, which in our case of layer
     * colors is equal to the number of pixels having the color identified
     * by the node.
     */
    private static class OctTree {

        /**
         * Maximum depth of the tree. Each node of this depth level
         * is automatically created as a leaf node.
         */
        private static final int MAX_DEPTH = 8;

        /**
	 * How many leafs do we have in the tree. This is the number of
	 * distinct colors managed in the tree.
	 */
        private int leafCount;

        /**
         * Keep a reference to the root node of the tree. This root node
         * is the start for all operations.
         */
        private final OctTreeNode root = new OctTreeNode(null);

        /**
         * Binary trees of all the leaf nodes at specific levels. Initially -
	 * before reduction - all nodes will be in the list number
	 * {@link #MAX_DEPTH}.
         */
        private final OctTreeNode[] redtable = new OctTreeNode[MAX_DEPTH+1];

        /** Counts of nodes contained in each of the lists. */
        private final int[] rednof = new int[MAX_DEPTH+1];

        /**
         * The maximum depth level still containing leaf nodes. This is
         * intially - before reduction - set to {@link #MAX_DEPTH} in the
	 * {@link #buildColorTree} method.
         */
        private int reddepth;

	public OctTree() {
	    for (int i=0; inull if no such color exists, which is highly
	 * 	unlikely under normal circumstances.
	 */
	public OctTreeNode getNode(int r, int g, int b) {

	    OctTreeNode node = root;
            int m = 1 << MAX_DEPTH;

            while (node != null) {

                // If the node is already a leaf node, return the index
                if (node.leaf) return node;

                // Calculate the child index for the next level
                m >>= 1;
                short c = 0;
                if ((r & m) != 0) c |= 4;
                if ((g & m) != 0) c |= 2;
                if ((b & m) != 0) c++;

                // and go to that child
                node = node.childs[c];

            }

            // If we get here the node is null and we didn't find anything.
            // This should only occurr while dithering
            return null;

	}

	/**
         * Insert or modify the leaf node for the given color. If a leaf for
         * the color does not exist yet, it will be created as are any missing
         * parent nodes. If it is existing, the nodes color is weighted by
         * the color.
         *
         * @param r The red color value of the new node
         * @param g The green color value of the new node
         * @param b The blue color value of the new node
         * @param count The number of pixels bearing the given color
         */
        public void insertNode(int r, int g, int b, int count) {

            OctTreeNode node = root;
            int m = 1 << MAX_DEPTH;

            while (node != null) {

                if (node.leaf) {

                    // if we are on leaf, set color */
                    node.nofcolors += count;
                    node.sr += r * count;
                    node.sg += g * count;
                    node.sb += b * count;

                    // we're done now, force end of loop
                    break;

                } else {

                    // we must go further down the tree
                    m >>= 1;
                    int c = 0;
                    if ((r & m) != 0) c |= 4;
                    if ((g & m) != 0) c |= 2;
                    if ((b & m) != 0) c |= 1; // faster than ++

                    // The requested child does not exist yet, create
                    if (node.childs[c] == null) {

                        // create a new child and increment counter
                        node = node.childs[c] = new OctTreeNode(node);

                        // Have we looked at the last bit ?
                        if (m == 1) {

                            // mark the node as a leaf node and increment counter
                            node.leaf = true;
                            leafCount++;

                            // insert the new leaf node at the previous position
                            // to the anchor node
                            insertNode(redtable[MAX_DEPTH], node);

                            // Increment the size of the circular list
                            rednof[MAX_DEPTH]++;

                            // Assert the maximum depth level
                            reddepth = MAX_DEPTH;

                        }

                    } else {

                        // Go on to the child
                        node = node.childs[c];

                    }

                }
            }
        }

	/**
	 * Returns true if the color tree has been reduced
	 */
	public boolean isReduced() {

	    /**
	     * check whether there is a reduction table, except the MAX_DEPTH
	     * one being not empty.
	     */

	    for (int i=MAX_DEPTH-1; i>= 0; i--) {
		if (rednof[i] != 0) {
		    return true;
		}
	    }

	    // no non-empty lists, if we get here
	    return false;
	}

        /**
         * Identifies a node to reduce and reduce its children. Thus the
         * tree will be reduced and contain upto 7 distinct colors less than
         * before. Nodes reduced away are removed from the tree.
         *
         * @throws NullPointerException if {@link #getReducibleNode} returns
         *    null which is considered a hard error.
         */
        public void reduceNode() {

            /**
             * According to the notes to {@link #getReducibleNode()} we won't
             * get null or we really have a problem, in which case
	     * it is legal to throw the NullPointerException if we access the node.
             */

            // Find a reducible node.
            OctTreeNode node = getReducibleNode();

            // Get the weighted color sum of the child nodes, which are
            // supposed to be leaf nodes.

            int sr = 0; // sum of red weights of children
	    int sg = 0; // sum of green weights of children
	    int sb = 0; // sum of blue weights of children
            int cc = 0; // sum of color weights of children
            int c = 0;  // the number child nodes reduced away

            for (int i=0; i<8; i++) {
                OctTreeNode child = node.childs[i];
                if (child != null) {
                    // adjust sums
                    c++;
                    sr += child.sr;
                    sg += child.sg;
                    sb += child.sb;
                    cc += child.nofcolors;

                    // remove child from redlist
		    deleteNode(redtable[child.depth], child);
                    rednof[child.depth]--;

		    // remove the child node
		    node.childs[i] = null;
                }
            }

            // make the reducible node the new leaf and set the color values
            node.leaf = true;
            node.nofcolors = cc;
            node.sr = sr;
	    node.sg = sg;
	    node.sb = sb;

            // insert new leaf into the red-table
            int d = node.depth;
	    insertNode(redtable[d], node);
            rednof[d]++;

            // Check whether we removed the last nodes at our children's level
            if (rednof[d+1] == 0) {
		reddepth--;
	    }

            // adjust nofcolors
            leafCount -= c - 1;
        }

        //---------- node management -------------------------------------------

	/**
	 * Creates and fills a color map.
	 *
	 * @param cmap The optional byte array to fill with the map. If this is
	 * 		null or not big enough to take all entries
	 * 		a new array is allocated.
	 *
	 * @return The color map either the input cmap or the newly allocated.
	 * 		See comments on cmap above.
	 */
	public byte[] createColorMap(byte[] cmap) {
	    final int mapSize = leafCount * 3;

	    if (cmap == null || cmap.length < mapSize) {
		cmap = new byte[ mapSize ];
	    }

	    for (int i=redtable.length-1, j=0; i >= 0 ; i--) {
		for (OctTreeNode n=redtable[i].next; n != null; n=n.next) {
		    // cache the map index in the node
		    n.nofcolors = j/3;

		    // store the color values in the map
		    cmap[j++] = (byte)(n.r & 0xff);
		    cmap[j++] = (byte)(n.g & 0xff);
		    cmap[j++] = (byte)(n.b & 0xff);
		}
	    }

	    return cmap;
	}

	/**
	 * Deletes the node from the tree defined by its root. If the tree is
	 * empty (root is null) or if the node is not found in the
	 * tree, the 'tree' remains unchanged.
	 *
	 * @param root The root of the tree to delete the node from.
	 * @param node The node to delete from the tree.
	 */
	private void deleteNode(OctTreeNode root, OctTreeNode node) {

	    OctTreeNode p = root;
	    OctTreeNode q = root.next;
	    while (q != null && q != node) {
		p = q;
		q = q.next;
	    }
	    // invariant : q == p.next && (q == null || q == node)

	    if (q == node) {
		p.next = node.next;

		// clean node references
		node.next = null;
	    }
	}

	/**
	 * Inserts the node into the binary reduction tree. If the tree is still
	 * empty, that is root is null, the node
	 * will become the root of the tree.
	 *
	 * @param root The root node of the binary tree or null to
	 * 	build a new tree with the node as the root.
	 * @param node The node to insert into the tree or to make the root node
	 * 	of a new tree.
	 */
	private void insertNode(OctTreeNode root, OctTreeNode node) {
	    OctTreeNode p = root;
	    OctTreeNode q = p.next;
	    while (q != null) {
		p = q;
		q = q.next;
	    }

	    p.next = node;
	    node.next = null;
	    // node.next = root.next;
	    // root.next = node;
	}

        /**
	 * Returns the parent of a reducible node. A node is reducible if the
	 * number of occurrences of the color, the node represents is less than
	 * or equal to the occurrences of all the colors in the same tree.
         *
         * @return The parent of the node with the least number of pixels or
         *      null if no such nodes exist. This latter case is considered
         *      a really hard error and MUST not occurr.
	 *
	 * @throws NullPointerException if the root parameter is
	 * 	null.
         */
        private OctTreeNode getReducibleNode() {

	    /**
	     * We assume this list to be relatively short, so the performance
	     * penalty of having to look in the complete list for a candidate
	     * node is small compared to the peformance penalty, we would face
	     * if the insertion and deletion of nodes would have to preserve
	     * ordering - esp. since the ordering criteria (nofcolors) is not
	     * constant.
	     */

	    // Get a head start for the pixel counter
            int m = Integer.MAX_VALUE;

            // Start a the anchor node
            OctTreeNode n = redtable[reddepth].next;

            OctTreeNode bn = null;
            for (; n != null; n = n.next) {
                if (n.nofcolors < m) {
                    m = n.nofcolors;
                    bn = n;
                }
            }

            // We should get a node with less than Integer.MAX_VALUE pixels
            // set, else we really have a problem....

            return (bn != null) ? bn.parent : null;

        }

    }

}