Class ErrorDiffusionDithering
- All Implemented Interfaces:
RGBIndex
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.setTemplateType(ErrorDiffusionDithering.TYPE_STUCKI); edd.setQuantizer(quantizer); edd.setInputImage(image); edd.process(); PixelImage quantizedImage = edd.getOutputImage();
Grayscale to black and white
In this example, aGray8Image
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
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Field Summary
FieldsModifier and TypeFieldDescriptionprivate static final int[][]
static final int
The default error diffusion type, to be used if none is specified by the user: (@link #TYPE_FLOYD_STEINBERG}.private int[]
private int[]
private static final int[][]
private int
private int
static final int
The index of the denominator of the relative part of the error of a neighbor pixel.static final int
The index of the numerator of the relative part of the error of a neighbor pixel.static final int
The index for the horizontal position of a neighbor pixel.static final int
The index for the vertical position of a neighbor pixel.private int[]
private static final int[][]
private int
private int
private int
private RGBQuantizer
private int
private static final int[][]
private static final int[][]
private static final int[][]
private int[][]
static final int
Constant for Burkes error diffusion.static final int
Constant for Floyd-Steinberg error diffusion.static final int
Constant for Burkes error diffusion.static final int
Constant for Burkes error diffusion.static final int
Constant for Burkes error diffusion.static final int
Constant for Stucki error diffusion.private boolean
Fields inherited from interface net.sourceforge.jiu.data.RGBIndex
INDEX_BLUE, INDEX_GREEN, INDEX_RED
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Constructor Summary
ConstructorsConstructorDescriptionCreates a new object of this class and set the dithering type toDEFAULT_TYPE
. -
Method Summary
Modifier and TypeMethodDescriptionprivate static int
adjust
(int value, int max) Clamps the argument value to interval 0..max.private void
fillBuffer
(int channelIndex, int rowIndex, int[] dest, int destOffset) Copies data from input image to argument buffer.private void
init
(int[][] data, int imageWidth) void
process()
Quantizes the input image, distributing quantization errors to neighboring pixels.private void
process
(Gray8Image in, BilevelImage out) private void
process
(Gray8Image in, Gray8Image out) private void
process
(RGB24Image in, Paletted8Image out) private void
process
(RGB24Image in, RGB24Image out) void
setGrayscaleOutputBits
(int numBits) Sets the number of bits to be in the output image when a grayscale image is quantized.void
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 anRGBIntegerImage
(true
) or aPaletted8Image
(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
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Field Details
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TYPE_FLOYD_STEINBERG
public static final int TYPE_FLOYD_STEINBERGConstant for Floyd-Steinberg error diffusion. The quantization error is distributed to four neighboring pixels.- See Also:
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TYPE_STUCKI
public static final int TYPE_STUCKIConstant for Stucki error diffusion. The quantization error is distributed to twelve neighboring pixels.- See Also:
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TYPE_BURKES
public static final int TYPE_BURKESConstant for Burkes error diffusion. The quantization error is distributed to seven neighboring pixels.- See Also:
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TYPE_SIERRA
public static final int TYPE_SIERRAConstant for Burkes error diffusion. The quantization error is distributed to ten neighboring pixels.- See Also:
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TYPE_JARVIS_JUDICE_NINKE
public static final int TYPE_JARVIS_JUDICE_NINKEConstant for Burkes error diffusion. The quantization error is distributed to twelve neighboring pixels.- See Also:
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TYPE_STEVENSON_ARCE
public static final int TYPE_STEVENSON_ARCEConstant for Burkes error diffusion. The quantization error is distributed to twelve neighboring pixels.- See Also:
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DEFAULT_TYPE
public static final int DEFAULT_TYPEThe default error diffusion type, to be used if none is specified by the user: (@link #TYPE_FLOYD_STEINBERG}.- See Also:
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INDEX_X_POS
public static final int INDEX_X_POSThe index for the horizontal position of a neighbor pixel. For a description, see the constructorsetTemplateData(int[][])
.- See Also:
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INDEX_Y_POS
public static final int INDEX_Y_POSThe index for the vertical position of a neighbor pixel. For a description, see the constructorsetTemplateData(int[][])
.- See Also:
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INDEX_ERROR_NUMERATOR
public static final int INDEX_ERROR_NUMERATORThe index of the numerator of the relative part of the error of a neighbor pixel. For a description, see the constructorsetTemplateData(int[][])
.- See Also:
-
INDEX_ERROR_DENOMINATOR
public static final int INDEX_ERROR_DENOMINATORThe index of the denominator of the relative part of the error of a neighbor pixel. For a description, see the constructorsetTemplateData(int[][])
.- See Also:
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FLOYD_STEINBERG_DATA
private static final int[][] FLOYD_STEINBERG_DATA -
STUCKI_DATA
private static final int[][] STUCKI_DATA -
BURKES_DATA
private static final int[][] BURKES_DATA -
SIERRA_DATA
private static final int[][] SIERRA_DATA -
JARVIS_JUDICE_NINKE_DATA
private static final int[][] JARVIS_JUDICE_NINKE_DATA -
STEVENSON_ARCE_DATA
private static final int[][] STEVENSON_ARCE_DATA -
grayBits
private int grayBits -
imageWidth
private int imageWidth -
leftColumns
private int leftColumns -
rightColumns
private int rightColumns -
newWidth
private int newWidth -
numRows
private int numRows -
templateData
private int[][] templateData -
errorNum
private int[] errorNum -
errorDen
private int[] errorDen -
indexLut
private int[] indexLut -
quantizer
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useTruecolorOutput
private boolean useTruecolorOutput
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Constructor Details
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ErrorDiffusionDithering
public ErrorDiffusionDithering()Creates a new object of this class and set the dithering type toDEFAULT_TYPE
.
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Method Details
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adjust
private static int adjust(int value, int max) Clamps the argument value to interval 0..max.- Parameters:
value
- the value to be adjustedmax
- the maximum allowed value (minimum is always 0)- Returns:
- the adjusted value
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fillBuffer
private void fillBuffer(int channelIndex, int rowIndex, int[] dest, int destOffset) Copies data from input image to argument buffer.- Parameters:
channelIndex
- index of the channel of the input image from which data is to be copiedrowIndex
- index of the row of the input image from which data is to be copieddest
- the array to which data is to be copieddestOffset
- index of the first element in the dest array to which data will be copied
-
init
private void init(int[][] data, int imageWidth) -
process
Quantizes the input image, distributing quantization errors to neighboring pixels. Works forGray8Image
(thensetGrayscaleOutputBits(int)
must have been called to set a number of output bits between 1 and 7) objects andRGB24Image
(then a quantizer must be specified usingsetQuantizer(RGBQuantizer)
) objects.- Overrides:
process
in classOperation
- Throws:
MissingParameterException
- if any mandatory parameter was not given to the operationWrongParameterException
- if at least one of the input parameters was not initialized appropriately (values out of the valid interval, etc.)
-
process
-
process
-
process
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process
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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 typeGray8Image
, only values between 1 and 7 are valid.- Parameters:
numBits
- the number of bits in the output image
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setQuantizer
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
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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 ofdata
describe one neighboring pixel and the relative amount of the error that it gets. That is whydata.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.INDEX_X_POS
(0): the difference between the horizontal position of the current pixel, x, and the neighboring pixel; can take a positive or negative value, or zero; exception: the y position of the current pixel is zero; in that case, this value must be larger than zero, because neighboring pixels that get part of the error must be to the right of or below the current pixelINDEX_Y_POS
(1): the difference between the vertical position of the current pixel, y, and the neighboring pixel; must be equal to or larger than 0INDEX_ERROR_NUMERATOR
(2): the numerator of the relative part of the error that wil be added to this neighboring pixel; must not be equal to 0INDEX_ERROR_DENOMINATOR
(3): the denominator of the relative part of the error that wil be added to this neighboring pixel; must not be equal to 0
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
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setTruecolorOutput
public void setTruecolorOutput(boolean truecolor) When dithering an RGB input image, this method specifies whether the output will be anRGBIntegerImage
(true
) or aPaletted8Image
(false
).- Parameters:
truecolor
- true if truecolor output is wanted
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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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