/**
* Calculates the final BitMatrix once for all requests. This could be called once from the
* constructor instead, but there are some advantages to doing it lazily, such as making profiling
* easier, and not doing heavy lifting when callers don't expect it.
*/
@Override
public BitMatrix getBlackMatrix() throws NotFoundException {
if (matrix != null) {
return matrix;
}
LuminanceSource source = getLuminanceSource();
int width = source.getWidth();
int height = source.getHeight();
if (width >= MINIMUM_DIMENSION && height >= MINIMUM_DIMENSION) {
byte[] luminances = source.getMatrix();
int subWidth = width >> BLOCK_SIZE_POWER;
if ((width & BLOCK_SIZE_MASK) != 0) {
subWidth++;
}
int subHeight = height >> BLOCK_SIZE_POWER;
if ((height & BLOCK_SIZE_MASK) != 0) {
subHeight++;
}
int[][] blackPoints = calculateBlackPoints(luminances, subWidth, subHeight, width, height);
BitMatrix newMatrix = new BitMatrix(width, height);
calculateThresholdForBlock(
luminances, subWidth, subHeight, width, height, blackPoints, newMatrix);
matrix = newMatrix;
} else {
// If the image is too small, fall back to the global histogram approach.
matrix = super.getBlackMatrix();
}
return matrix;
}
