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net.sourceforge.jiu.color.dithering
Class ErrorDiffusionDithering

java.lang.Object
  extended bynet.sourceforge.jiu.ops.Operation
      extended bynet.sourceforge.jiu.ops.ImageToImageOperation
          extended bynet.sourceforge.jiu.color.dithering.ErrorDiffusionDithering
All Implemented Interfaces:
RGBIndex

public class ErrorDiffusionDithering
extends ImageToImageOperation
implements RGBIndex

This class is used to apply error diffusion dithering to images that are being reduced in their color depth. Works with GrayIntegerImage and RGBIntegerImage objects. For RGB images, a quantizer must be specified via setQuantizer(net.sourceforge.jiu.color.quantization.RGBQuantizer). That quantizer must have been initialized (it must have searched for / given a palette that it can map to).

This class offers six predefined types of error diffusion dithering. In addition, user-defined types can be integrated by providing a information on how the error is to be distributed; see the description of setTemplateData(int[][]).

Usage examples

Color

This small program maps some RGB24Image object to a Paletted8Image with 120 entries in its palette, using Stucki error diffusion dithering in combination with an octree color quantizer.
 MemoryRGB24Image image = ...; // some RGB image
 OctreeColorQuantizer quantizer = new OctreeColorQuantizer();
 quantizer.setInputImage(image);
 quantizer.setPaletteSize(120);
 quantizer.init();
 ErrorDiffusionDithering edd = new ErrorDiffusionDithering();
 edd.setType(ErrorDiffusionDithering.TYPE_STUCKI);
 edd.setQuantizer(quantizer);
 edd.setInputImage(image);
 edd.process();
 PixelImage quantizedImage = edd.getOutputImage();
 

Grayscale to black and white

In this example, a Gray8Image object is reduced to black and white using Floyd-Steinberg dithering.
 Gray8Image image = ...; // some grayscale image
 ErrorDiffusionDithering edd = new ErrorDiffusionDithering();
 edd.setGrayscaleOutputBits(1);
 edd.setInputImage(image);
 edd.process();
 PixelImage ditheredImage = edd.getOutputImage();
 // if you need something more specific than PixelImage: 
 BilevelImage output = null;
 // ditheredImage should be a BilevelImage...
 if (ditheredImage instanceof BilevelImage
 {
   // ... and it is!
   output = (BilevelImage)ditheredImage;
 }
 

TODO

Adjust this class to be able to process 16 bits per sample.

Theoretical background

The predefined templates were taken from the book Bit-mapped graphics (2nd edition) by Steve Rimmer, published by Windcrest / McGraw-Hill, ISBN 0-8306-4208-0. The part on error diffusion dithering starts on page 375.

Several sources recommend Robert Ulichney's book Digital Halftoning for this topic (published by The MIT Press, ISBN 0-262-21009-6). Unfortunately, I wasn't able to get a copy (or the CD-ROM version published by Dr. Dobb's Journal).

Since:
0.5.0
Author:
Marco Schmidt

Field Summary
static int DEFAULT_TYPE
          The default error diffusion type, to be used if none is specified by the user.
static int INDEX_ERROR_DENOMINATOR
          The index of the denominator of the relative part of the error of a neighbor pixel.
static int INDEX_ERROR_NUMERATOR
          The index of the numerator of the relative part of the error of a neighbor pixel.
static int INDEX_X_POS
          The index for the horizontal position of a neighbor pixel.
static int INDEX_Y_POS
          The index for the vertical position of a neighbor pixel.
static int TYPE_BURKES
          Constant for Burkes error diffusion.
static int TYPE_FLOYD_STEINBERG
          Constant for Floyd-Steinberg error diffusion.
static int TYPE_JARVIS_JUDICE_NINKE
          Constant for Burkes error diffusion.
static int TYPE_SIERRA
          Constant for Burkes error diffusion.
static int TYPE_STEVENSON_ARCE
          Constant for Burkes error diffusion.
static int TYPE_STUCKI
          Constant for Stucki error diffusion.
 
Fields inherited from interface net.sourceforge.jiu.data.RGBIndex
INDEX_BLUE, INDEX_GREEN, INDEX_RED
 
Constructor Summary
ErrorDiffusionDithering()
          Creates a new object of this class and set the dithering type to DEFAULT_TYPE.
 
Method Summary
 void process()
          Quantizes the input image, distributing quantization errors to neighboring pixels.
 void setGrayscaleOutputBits(int numBits)
          Sets the number of bits to be in the output image when a grayscale image is quantized.
 void setQuantizer(RGBQuantizer q)
          Sets the color quantizer to be used (if the input image is a truecolor image).
 void setTemplateData(int[][] data)
          Set information on how errors are to be distributed by this error diffusion dithering operation.
 void setTemplateType(int type)
          Sets a new template type.
 void setTruecolorOutput(boolean truecolor)
          When dithering an RGB input image, this method specifies whether the output will be an RGBIntegerImage (true) or a Paletted8Image (false).
 
Methods inherited from class net.sourceforge.jiu.ops.ImageToImageOperation
canInputAndOutputBeEqual, ensureImagesHaveSameResolution, ensureInputImageIsAvailable, ensureOutputImageResolution, getInputImage, getOutputImage, setCanInputAndOutputBeEqual, setInputImage, setOutputImage
 
Methods inherited from class net.sourceforge.jiu.ops.Operation
addProgressListener, addProgressListeners, getAbort, removeProgressListener, setAbort, setProgress, setProgress
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

TYPE_FLOYD_STEINBERG

public static final int TYPE_FLOYD_STEINBERG
Constant for Floyd-Steinberg error diffusion. The quantization error is distributed to four neighboring pixels.

See Also:
Constant Field Values

TYPE_STUCKI

public static final int TYPE_STUCKI
Constant for Stucki error diffusion. The quantization error is distributed to twelve neighboring pixels.

See Also:
Constant Field Values

TYPE_BURKES

public static final int TYPE_BURKES
Constant for Burkes error diffusion. The quantization error is distributed to seven neighboring pixels.

See Also:
Constant Field Values

TYPE_SIERRA

public static final int TYPE_SIERRA
Constant for Burkes error diffusion. The quantization error is distributed to ten neighboring pixels.

See Also:
Constant Field Values

TYPE_JARVIS_JUDICE_NINKE

public static final int TYPE_JARVIS_JUDICE_NINKE
Constant for Burkes error diffusion. The quantization error is distributed to twelve neighboring pixels.

See Also:
Constant Field Values

TYPE_STEVENSON_ARCE

public static final int TYPE_STEVENSON_ARCE
Constant for Burkes error diffusion. The quantization error is distributed to twelve neighboring pixels.

See Also:
Constant Field Values

DEFAULT_TYPE

public static final int DEFAULT_TYPE
The default error diffusion type, to be used if none is specified by the user.

See Also:
Constant Field Values

INDEX_X_POS

public static final int INDEX_X_POS
The index for the horizontal position of a neighbor pixel. For a description, see the constructor setTemplateData(int[][]).

See Also:
Constant Field Values

INDEX_Y_POS

public static final int INDEX_Y_POS
The index for the vertical position of a neighbor pixel. For a description, see the constructor setTemplateData(int[][]).

See Also:
Constant Field Values

INDEX_ERROR_NUMERATOR

public static final int INDEX_ERROR_NUMERATOR
The index of the numerator of the relative part of the error of a neighbor pixel. For a description, see the constructor setTemplateData(int[][]).

See Also:
Constant Field Values

INDEX_ERROR_DENOMINATOR

public static final int INDEX_ERROR_DENOMINATOR
The index of the denominator of the relative part of the error of a neighbor pixel. For a description, see the constructor setTemplateData(int[][]).

See Also:
Constant Field Values
Constructor Detail

ErrorDiffusionDithering

public ErrorDiffusionDithering()
Creates a new object of this class and set the dithering type to DEFAULT_TYPE.

Method Detail

process

public void process()
             throws MissingParameterException,
                    WrongParameterException
Quantizes the input image, distributing quantization errors to neighboring pixels. Works for Gray8Image (then setGrayscaleOutputBits(int) must have been called to set a number of output bits between 1 and 7) objects and RGB24Image (then a quantizer must be specified using setQuantizer(RGBQuantizer)) objects.

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.)

setGrayscaleOutputBits

public void setGrayscaleOutputBits(int numBits)
Sets the number of bits to be in the output image when a grayscale image is quantized. If the input image is of type Gray8Image, only values between 1 and 7 are valid.

Parameters:
numBits - the number of bits in the output image

setQuantizer

public void setQuantizer(RGBQuantizer q)
Sets the color quantizer to be used (if the input image is a truecolor image).

Parameters:
q - an object of a class implementing the RGBQuantizer interface

setTemplateData

public void setTemplateData(int[][] data)
Set information on how errors are to be distributed by this error diffusion dithering operation.

Error diffusion dithering works by quantizing each pixel and distributing the resulting error to neighboring pixels. Quantizing maps a pixel to another pixel. Each pixel is made up of one or more samples (as an example, three samples rorig, gorig and borig for the original pixel of an RGB image and rquant, gquant and bquant for the quantized pixel).

The process of quantization attempts to find a quantized pixel that is as close to the original as possible. In the ideal case, the difference between original and quantized pixel is zero for each sample. Otherwise, this quantization error is non-zero, positive or negative. Example: original pixel (12, 43, 33), quantized pixel (10, 47, 40); the error is (12 - 10, 43 - 47, 40 - 33) = (2, -4, 7). The error (2, -4, 7) is to be distributed to neighboring pixels.

The data argument of this constructor describes how to do that. It is a two-dimensional array of int values. Each of the one-dimensional int arrays of data describe one neighboring pixel and the relative amount of the error that it gets. That is why data.length specifies the number of neighboring pixels involved in distributing the error. Let's call the pixel that was just quantized the current pixel. It is at image position (x, y).

Each of the one-dimensional arrays that are part of data must have a length of 4. The meaning of these four values is now described. The values can be accessed by the INDEX_xyz constants of this class. These four values describe the position of one neighboring pixel and the relative amount of the error that will be added to or subtracted from it.

Example: the predefined dithering type Floyd-Steinberg. It has the following data array:
 int[][] FLOYD_STEINBERG = {{ 1,  0, 7, 16},
   {-1,  1, 3, 16},
   { 0,  1, 5, 16},
   { 1,  1, 1, 16}};
 
Each of the one-dimensional arrays is of length 4. Accidentally, there are also four one-dimensional arrays. The number of arrays is up to the designer. The first array {1, 0, 7, 16} is interpreted as follows--go to the pixel with a horizontal difference of 1 and a vertical difference of 0 (so, the pixel to the right of the current pixel) and add 7 / 16th of the quantization error to it. Then go to the pixel at position (-1, 1) (one to the left, one row below the current row) and add 3 / 16th of the error to it. The other two one-dimensional arrays are processed just like that.

As you can see, the four relative errors 1/16, 3/16, 5/16 and 7/16 sum up to 1 (or 16/16); this is in a precondition to make sure that the error is distributed completely.

Parameters:
data - contains a description of how the error is to be distributed

setTruecolorOutput

public void setTruecolorOutput(boolean truecolor)
When dithering an RGB input image, this method specifies whether the output will be an RGBIntegerImage (true) or a Paletted8Image (false).

Parameters:
truecolor - true if truecolor output is wanted

setTemplateType

public void setTemplateType(int type)
Sets a new template type. The argument must be one of the TYPE_xyz constants of this class.

Parameters:
type - int value, one of the TYPE_xyz constants of this class
Throws:
IllegalArgumentException - if the argument is not of the TYPE_xyz constants

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Copyright © 2000, 2001, 2002, 2003, 2004 Marco Schmidt