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java.lang.Object | +--fi.faidon.jis.JPEGSample
This file is more or less a translation of the jcsample.c file of the Independent JPEG Group's software. This file contains downsampling routines. Downsampling input data is counted in "row groups". A row group is defined to be max_v_samp_factor pixel rows of each component, from which the downsampler produces v_samp_factor sample rows. A single row group is processed in each call to the downsampler module. The downsampler is responsible for edge-expansion of its output data to fill an integral number of DCT blocks horizontally. The source buffer may be modified if it is helpful for this purpose (the source buffer is allocated wide enough to correspond to the desired output width). The caller (the prep controller) is responsible for vertical padding. The downsampler may request "context rows" by setting need_context_rows during startup. In this case, the input arrays will contain at least one row group's worth of pixels above and below the passed-in data; the caller will create dummy rows at image top and bottom by replicating the first or last real pixel row. An excellent reference for image resampling is Digital Image Warping, George Wolberg, 1990. Pub. by IEEE Computer Society Press, Los Alamitos, CA. ISBN 0-8186-8944-7. The downsampling algorithm used here is a simple average of the source pixels covered by the output pixel. The hi-falutin sampling literature refers to this as a "box filter". In general the characteristics of a box filter are not very good, but for the specific cases we normally use (1:1 and 2:1 ratios) the box is equivalent to a "triangle filter" which is not nearly so bad. If you intend to use other sampling ratios, you'd be well advised to improve this code. A simple input-smoothing capability is provided. This is mainly intended for cleaning up color-dithered GIF input files (if you find it inadequate, we suggest using an external filtering program such as pnmconvol). When enabled, each input pixel P is replaced by a weighted sum of itself and its eight neighbors. P's weight is 1-8*SF and each neighbor's weight is SF, where SF = (smoothing_factor / 1024). Currently, smoothing is only supported for 2h2v sampling factors.
Field Summary | |
boolean |
needContextRows
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Constructor Summary | |
JPEGSample(JPEGImageSaver cinfo)
Module initialization routine for downsampling. |
Method Summary | |
void |
downsample(JPEGImageSaver cinfo,
java.util.Vector inputBuf,
int inRowIndex,
java.util.Vector outputBuf,
int outRowGroupIndex)
Replaces the downsample function pointer of the original C source. |
void |
expandRightEdge(int[][] imageData,
int inRowOff,
int numRows,
int inputCols,
int outputCols)
Expand a component horizontally from width input_cols to width output_cols, by duplicating the rightmost samples. |
void |
intDownsample(JPEGImageSaver cinfo,
JPEGComponentInfo comp,
int[][] inputData,
int inRowOff,
int[][] outputData,
int outRowOff)
Downsample pixel values of a single component. |
void |
sepDownsample(JPEGImageSaver cinfo,
java.util.Vector inputBuf,
int inRowIndex,
java.util.Vector outputBuf,
int outRowGroupIndex)
Do downsampling for a whole row group (all components). |
void |
startPass(JPEGImageSaver cinfo)
Replaces the start_pass function pointer of the original C source. |
void |
startPassDownsample(JPEGImageSaver cinfo)
Initialize for a downsampling pass. |
Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Field Detail |
public boolean needContextRows
Constructor Detail |
public JPEGSample(JPEGImageSaver cinfo) throws java.io.IOException
Method Detail |
public void startPass(JPEGImageSaver cinfo)
public void startPassDownsample(JPEGImageSaver cinfo)
public void expandRightEdge(int[][] imageData, int inRowOff, int numRows, int inputCols, int outputCols)
public void downsample(JPEGImageSaver cinfo, java.util.Vector inputBuf, int inRowIndex, java.util.Vector outputBuf, int outRowGroupIndex)
public void sepDownsample(JPEGImageSaver cinfo, java.util.Vector inputBuf, int inRowIndex, java.util.Vector outputBuf, int outRowGroupIndex)
public void intDownsample(JPEGImageSaver cinfo, JPEGComponentInfo comp, int[][] inputData, int inRowOff, int[][] outputData, int outRowOff)
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