Qtable(boolean wantLuma, float quality) {
elementPrecision = 0;
JPEGQTable base = null;
if (wantLuma) {
tableID = 0;
base = JPEGQTable.K1Div2Luminance;
} else {
tableID = 1;
base = JPEGQTable.K2Div2Chrominance;
}
if (quality != JPEG.DEFAULT_QUALITY) {
quality = JPEG.convertToLinearQuality(quality);
if (wantLuma) {
base = JPEGQTable.K1Luminance.getScaledInstance(quality, true);
} else {
base = JPEGQTable.K2Div2Chrominance.getScaledInstance(quality, true);
}
}
data = base.getTable();
}
/**
* Assuming the given table was generated by scaling the "standard" visually lossless luminance
* table, extract the scale factor that was used.
*/
Qtable getChromaForLuma(Qtable luma) {
Qtable newGuy = null;
// Determine if the table is all the same values
// if so, use the same table
boolean allSame = true;
for (int i = 1; i < luma.QTABLE_SIZE; i++) {
if (luma.data[i] != luma.data[i - 1]) {
allSame = false;
break;
}
}
if (allSame) {
newGuy = (Qtable) luma.clone();
newGuy.tableID = 1;
} else {
// Otherwise, find the largest coefficient less than 255. This is
// the largest value that we know did not clamp on scaling.
int largestPos = 0;
for (int i = 1; i < luma.QTABLE_SIZE; i++) {
if (luma.data[i] > luma.data[largestPos]) {
largestPos = i;
}
}
// Compute the scale factor by dividing it by the value in the
// same position from the "standard" table.
// If the given table was not generated by scaling the standard,
// the resulting table will still be reasonable, as it will reflect
// a comparable scaling of chrominance frequency response of the
// eye.
float scaleFactor =
((float) (luma.data[largestPos]))
/ ((float) (JPEGQTable.K1Div2Luminance.getTable()[largestPos]));
// generate a new table
JPEGQTable jpegTable = JPEGQTable.K2Div2Chrominance.getScaledInstance(scaleFactor, true);
newGuy = new Qtable(jpegTable, 1);
}
return newGuy;
}
