Class MedianCutQuantizer

  • All Implemented Interfaces:
    RGBQuantizer, RGBIndex

    public class MedianCutQuantizer
    extends ImageToImageOperation
    implements RGBIndex, RGBQuantizer
    Performs the Median Cut color quantization algorithm for a given list of colors.

    Supported image types

    The input image must implement RGB24Image.

    Usage example

    The following code snippet uses the default settings with a palette of 256 entries.
     MedianCutQuantizer quantizer = new MedianCutQuantizer();
     quantizer.setInputImage(image);
     quantizer.setPaletteSize(256);
     quantizer.process();
     PixelImage quantizedImage = quantizer.getOutputImage();
     
    If you want to combine Median Cut quantization with error diffusion dithering to improve the visual quality of the output, try the ErrorDiffusionDithering class. However, note that noise is introduced into the image with dithering methods so that the resulting image may not be suitable for automatic processing.

    Credits

    The Median Cut algorithm was designed by Paul Heckbert. He described it in the article Color image quantization for frame buffer display. Comput. Graphics 16(3), 1982, 297 - 304. CiteSeer page of the article.
    Author:
    Marco Schmidt
    See Also:
    MedianCutContourRemoval, ErrorDiffusionDithering
    • Field Detail

      • METHOD_REPR_COLOR_AVERAGE

        public static final int METHOD_REPR_COLOR_AVERAGE
        Constant value for a method of determining the representative color for a set of colors by computing the average of all samples for each of the three components red, green and blue. #getMethodToDetermineRepresentativeColors #setMethodToDetermineRepresentativeColors
        See Also:
        Constant Field Values
      • METHOD_REPR_COLOR_WEIGHTED_AVERAGE

        public static final int METHOD_REPR_COLOR_WEIGHTED_AVERAGE
        Constant value for a method of determining the representative color for a set of colors by computing the weighted average of all samples for each of the three components red, green and blue. Weighted means that each color is multiplied by the number of times it occurs in the input image. The values of samples multiplied by their frequency are then divided by the total number of times the colors appear in the image. #getMethodToDetermineRepresentativeColors #setMethodToDetermineRepresentativeColors
        See Also:
        Constant Field Values
      • METHOD_REPR_COLOR_MEDIAN

        public static final int METHOD_REPR_COLOR_MEDIAN
        Constant value for a method of determining the representative color for a set of colors by picking the median value of all samples for each of the three components red, green and blue. #getMethodToDetermineRepresentativeColors #setMethodToDetermineRepresentativeColors
        See Also:
        Constant Field Values
      • doNotMap

        private boolean doNotMap
      • maxValue

        private int maxValue
      • method

        private int method
      • outputTruecolor

        private boolean outputTruecolor
      • paletteSize

        private int paletteSize
    • Constructor Detail

      • MedianCutQuantizer

        public MedianCutQuantizer()
        Creates a MedianCutQuantizer object and initializes its fields to default values.
    • Method Detail

      • createLeafList

        public MedianCutNode[] createLeafList()
        Creates a linear list of leaf nodes. Assumes that findPalette() was successfully run before.
      • createPalette

        public Palette createPalette()
        Creates a palette with the representative colors of all leaf nodes. Assumes that findPalette() was successfully run before.
        Specified by:
        createPalette in interface RGBQuantizer
        Returns:
        palette with all representative colors
      • findLeafToBeSplit

        private MedianCutNode findLeafToBeSplit​(MedianCutNode node)
        Traverses tree given by argument node and returns leaf with largest distribution of samples for any of its three components.
      • findNearestNeighbor

        public MedianCutNode findNearestNeighbor​(int[] rgb)
        For a given RGB value, searches the node in the internal node tree whose representative color is closest to this color.
        Parameters:
        rgb - the color for which a match is searched; the array must have at least three entries; RGBIndex constants are used to address the samples
        Returns:
        node with best match
      • findNearestNeighbor

        public int findNearestNeighbor​(MedianCutNode[] nodes,
                                       int red,
                                       int green,
                                       int blue)
        For each node in the argument array computes the distance between the representative color of that node and the color given by the three argument samples.
        Returns:
        index of the node with the smallest distance or -1 if the array has a length of 0
      • findPalette

        public void findPalette()
      • findAllRepresentativeColors

        public void findAllRepresentativeColors()
      • findRepresentativeColor

        private int[] findRepresentativeColor​(int index1,
                                              int index2)
        Computes a representative color for a set of colors in the color list. Returns the color as a length three int array of sample values (which can be accessed using the index constants from RGBIndex. The method of determining the color (the REPR_xxx constants from this class) has been given to the constructor.
      • findRepresentativeColors

        private void findRepresentativeColors​(MedianCutNode node)
        Calls findRepresentativeColor with node if node is a leaf. Otherwise, recursively calls itself with both successor nodes.
      • getMethodToDetermineRepresentativeColors

        public int getMethodToDetermineRepresentativeColors()
        Returns the method (to be) used to determine the representative color for the list of colors of a node. Default is DEFAULT_METHOD_REPR_COLOR.
        Returns:
        the method, one of the METHOD_xyz constants
      • getPaletteSize

        public int getPaletteSize()
        Returns the number of colors in the destination image. If output is paletted, this is also the number of entries in the palette.
        Returns:
        number of colors in the destination
      • getTruecolorOutput

        public boolean getTruecolorOutput()
        Returns if this operation is supposed to generate truecolor or paletted output.
        Returns:
        if truecolor images are to be generated
        See Also:
        setTruecolorOutput(boolean)
      • map

        public int map​(int[] origRgb,
                       int[] quantizedRgb)
        Description copied from interface: RGBQuantizer
        This method maps a triplet of intensity values to its quantized counterpart and returns the palette index of that quantized color. The index values for the two arrays are taken from RGBIndex.
        Specified by:
        map in interface RGBQuantizer
        Parameters:
        origRgb - the three samples red, green and blue for which a good match is searched in the palette
        quantizedRgb - will hold the three samples found to be closest to origRgb after the call to this method
        Returns:
        int index in the palette of the match quantizedRgb
      • setAllPaletteIndexValues

        public void setAllPaletteIndexValues()
      • setMapping

        public void setMapping​(boolean doMap)
        Defines whether process will map the input image to an output image. If not, only the palette is determined.
      • setMethodToDetermineRepresentativeColors

        public void setMethodToDetermineRepresentativeColors​(int newMethod)
        Sets the method to determine the representative color for a list of colors. After the algorithm has determined sets of colors that lie closely together in color space and will be mapped to the same color in the destination image, the algorithm will determine that color
        Parameters:
        newMethod - the new method, one of the METHOD_xyz constants in this class
      • setPaletteIndexValues

        private int setPaletteIndexValues​(MedianCutNode node,
                                          int index)
        Recursively visits node and its descendants, assigning ascending palette index values to leaves via MedianCutNode.setPaletteIndex(int). If this method is called with root and 0 as parameters, all leaves will get a unique palette index.
      • setPaletteSize

        public void setPaletteSize​(int newPaletteSize)
        Sets the number of colors that this operations is supposed to reduce the original image to.
        Parameters:
        newPaletteSize - the number of colors
        Throws:
        IllegalArgumentException - if the argument is smaller than 1 or larger than 256
        See Also:
        getPaletteSize()
      • setTruecolorOutput

        public void setTruecolorOutput​(boolean useTruecolor)
        Lets the user specify if the output image is to be truecolor (argument useTruecolor is true) or paletted (argument useTruecolor is false). If the color type is to be changed afterwards, use PromoteToRgb24 to convert from paletted to truecolor. Reducing a truecolor image that uses only 256 or less colors to a paletted image can be done with AutoDetectColorType.
        Parameters:
        useTruecolor -