nom.tam.fits.compression.provider.param.quant.ZDither0Parameter Maven / Gradle / Ivy
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package nom.tam.fits.compression.provider.param.quant;
import nom.tam.fits.Header;
/*
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import nom.tam.fits.HeaderCard;
import nom.tam.fits.HeaderCardException;
import nom.tam.fits.compression.algorithm.quant.QuantizeOption;
import nom.tam.fits.compression.provider.param.base.CompressHeaderParameter;
import nom.tam.fits.header.Compression;
/**
* (for internal use) The The random seed initialization parameter as recorded in the FITS header.
*
* The storing of the random seed provides consistent dither implementations. Dithering adds a small amount of noise (at
* the level of the quantization level increments) to remove possible systematics biases of the quantization. Since the
* quantization (integer representation of floating-point values) is inherently lossy (noisy) the added dithering noise
* is generally inconsequential in terms of preseving information in the original image. As such, the image can be
* recovered close enough to the original, within the level of the quantization noise, without knowing the exact random
* sequence that was used to generate the dither.
*
*
* However, The FITS standard requires that when dithering is used in the compression the same tool (or library) should
* also undo the dithering exactly using the same sequence of random numbers as was used when compressing the image.
* Furthermore, the standard makes some explicit suggestions on how pseudo-random sequences should be generated, and
* offers a specific convention for an algorithm that may be used to provide consistent dithering across tools,
* platforms, and library implementations.
*
*
* For the dithering to be reversible, the FITS header should store the integer value, usually between 1 and 10000
* inclusive, under the ZDITHER0 keyword to indicate the value (random sequence index) that was used for
* seeding the random number generator according to the described standard.
*
*
* The nom-tam FITS library implements the suggested convention for the random number generator, and this parameter
* deals with recording the corresponding random seed value via the ZDITHER0 keyword in the compressed
* image headers; as well as retrieving this value to seed the random number generator when decompressing the image, in
* a way that is consistent with the FITS standard and recommended convention.
*
*
* @author Attila Kovacs
*/
final class ZDither0Parameter extends CompressHeaderParameter {
/**
* Creates a new compression parameter that can be used to configure the quantization options when cmpressing /
* decompressing image tiles.
*
* @param quantizeOption The quantization option that will be configured using this particular parameter.
*/
ZDither0Parameter(QuantizeOption quantizeOption) {
super(Compression.ZDITHER0.name(), quantizeOption);
}
@Override
public void getValueFromHeader(Header header) throws HeaderCardException {
if (getOption() == null) {
return;
}
HeaderCard card = header.getCard(Compression.ZDITHER0);
getOption().setSeed(card == null ? 1L : card.getValue(Long.class, 1L));
}
@Override
public void setValueInHeader(Header header) throws HeaderCardException {
if (getOption() == null) {
return;
}
header.addValue(Compression.ZDITHER0, (int) getOption().getSeed());
}
/**
* Seeds the random generator for the specific tile
*
* @param index the 0-based tile index.
*
* @throws NullPointerException if the parameter is no linked to a {@link QuantizeOption} instance (that is
* null was specified in the constructor).
*/
void setTileIndex(int index) throws NullPointerException {
getOption().setTileIndex(index);
}
}