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:
  • Field Details

    • 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:
    • 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:
    • 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:
    • DEFAULT_METHOD_REPR_COLOR

      public static final int DEFAULT_METHOD_REPR_COLOR
      The default method to determine the representative color from a list of colors. Will be used if none is set by the user of this class via setMethodToDetermineRepresentativeColors(int).
      See Also:
    • doNotMap

      private boolean doNotMap
    • list

      private RGBColorList list
    • maxValue

      private int maxValue
    • method

      private int method
    • outputTruecolor

      private boolean outputTruecolor
    • paletteSize

      private int paletteSize
    • root

      private MedianCutNode root
  • Constructor Details

    • MedianCutQuantizer

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

    • addNodes

      private void addNodes(MedianCutNode[] nodeList, MedianCutNode node)
    • createColorList

      private RGBColorList createColorList(RGB24Image image) throws OperationFailedException
      Throws:
      OperationFailedException
    • 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:
    • 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
    • mapImage

      public void mapImage(RGB24Image in, RGB24Image out)
    • mapImage

      public void mapImage(RGB24Image in, Paletted8Image out)
    • process

      Description copied from class: Operation
      This method does the actual work of the operation. It must be called after all parameters have been given to the operation object.
      Overrides:
      process in class Operation
      Throws:
      MissingParameterException - if any mandatory parameter was not given to the operation
      WrongParameterException - if at least one of the input parameters was not initialized appropriately (values out of the valid interval, etc.)
      OperationFailedException
    • 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:
    • 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 -
    • splitNode

      public void splitNode(MedianCutNode node)