ReaderUtilpublic class ReaderUtil extends Object | This class contains utility methods that may be useful to ImageReader
plugins. Ideally these methods would be in the ImageReader base class
so that all subclasses could benefit from them, but that would be an
addition to the existing API, and it is not yet clear whether these methods
are universally useful, so for now we will leave them here. |
| Methods Summary |
|---|
| private static void | computeUpdatedPixels(int sourceOffset, int sourceExtent, int destinationOffset, int dstMin, int dstMax, int sourceSubsampling, int passStart, int passExtent, int passPeriod, int[] vals, int offset)
// We need to satisfy the congruences:
// dst = destinationOffset + (src - sourceOffset)/sourceSubsampling
//
// src - passStart == 0 (mod passPeriod)
// src - sourceOffset == 0 (mod sourceSubsampling)
//
// subject to the inequalities:
//
// src >= passStart
// src < passStart + passExtent
// src >= sourceOffset
// src < sourceOffset + sourceExtent
// dst >= dstMin
// dst <= dstmax
//
// where
//
// dst = destinationOffset + (src - sourceOffset)/sourceSubsampling
//
// For now we use a brute-force approach although we could
// attempt to analyze the congruences. If passPeriod and
// sourceSubsamling are relatively prime, the period will be
// their product. If they share a common factor, either the
// period will be equal to the larger value, or the sequences
// will be completely disjoint, depending on the relationship
// between passStart and sourceOffset. Since we only have to do this
// twice per image (once each for X and Y), it seems cheap enough
// to do it the straightforward way.
boolean gotPixel = false;
int firstDst = -1;
int secondDst = -1;
int lastDst = -1;
for (int i = 0; i < passExtent; i++) {
int src = passStart + i*passPeriod;
if (src < sourceOffset) {
continue;
}
if ((src - sourceOffset) % sourceSubsampling != 0) {
continue;
}
if (src >= sourceOffset + sourceExtent) {
break;
}
int dst = destinationOffset +
(src - sourceOffset)/sourceSubsampling;
if (dst < dstMin) {
continue;
}
if (dst > dstMax) {
break;
}
if (!gotPixel) {
firstDst = dst; // Record smallest valid pixel
gotPixel = true;
} else if (secondDst == -1) {
secondDst = dst; // Record second smallest valid pixel
}
lastDst = dst; // Record largest valid pixel
}
vals[offset] = firstDst;
// If we never saw a valid pixel, set width to 0
if (!gotPixel) {
vals[offset + 2] = 0;
} else {
vals[offset + 2] = lastDst - firstDst + 1;
}
// The period is given by the difference of any two adjacent pixels
vals[offset + 4] = Math.max(secondDst - firstDst, 1);
| | public static int[] | computeUpdatedPixels(java.awt.Rectangle sourceRegion, java.awt.Point destinationOffset, int dstMinX, int dstMinY, int dstMaxX, int dstMaxY, int sourceXSubsampling, int sourceYSubsampling, int passXStart, int passYStart, int passWidth, int passHeight, int passPeriodX, int passPeriodY)A utility method that computes the exact set of destination
pixels that will be written during a particular decoding pass.
The intent is to simplify the work done by readers in combining
the source region, source subsampling, and destination offset
information obtained from the ImageReadParam with
the offsets and periods of a progressive or interlaced decoding
pass.
int[] vals = new int[6];
computeUpdatedPixels(sourceRegion.x, sourceRegion.width,
destinationOffset.x,
dstMinX, dstMaxX, sourceXSubsampling,
passXStart, passWidth, passPeriodX,
vals, 0);
computeUpdatedPixels(sourceRegion.y, sourceRegion.height,
destinationOffset.y,
dstMinY, dstMaxY, sourceYSubsampling,
passYStart, passHeight, passPeriodY,
vals, 1);
return vals;
|
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