import com.google.zxing.Binarizer;
import com.google.zxing.LuminanceSource;
-import com.google.zxing.ReaderException;
+import com.google.zxing.NotFoundException;
/**
* This class implements a local thresholding algorithm, which while slower than the
super(source);
}
- public BitMatrix getBlackMatrix() throws ReaderException {
+ public BitMatrix getBlackMatrix() throws NotFoundException {
binarizeEntireImage();
return matrix;
}
// 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.
- private void binarizeEntireImage() throws ReaderException {
+ private void binarizeEntireImage() throws NotFoundException {
if (matrix == null) {
LuminanceSource source = getLuminanceSource();
if (source.getWidth() >= MINIMUM_DIMENSION && source.getHeight() >= MINIMUM_DIMENSION) {
int width = source.getWidth();
int height = source.getHeight();
int subWidth = width >> 3;
+ if ((width & 0x07) != 0) {
+ subWidth++;
+ }
int subHeight = height >> 3;
- int[][] blackPoints = calculateBlackPoints(luminances, subWidth, subHeight, width);
+ if ((height & 0x07) != 0) {
+ subHeight++;
+ }
+ int[][] blackPoints = calculateBlackPoints(luminances, subWidth, subHeight, width, height);
matrix = new BitMatrix(width, height);
- calculateThresholdForBlock(luminances, subWidth, subHeight, width, blackPoints, matrix);
+ calculateThresholdForBlock(luminances, subWidth, subHeight, width, height, blackPoints, matrix);
} else {
// If the image is too small, fall back to the global histogram approach.
matrix = super.getBlackMatrix();
}
// For each 8x8 block in the image, calculate the average black point using a 5x5 grid
- // of the blocks around it. Also handles the corner cases, but will ignore up to 7 pixels
- // on the right edge and 7 pixels at the bottom of the image if the overall dimensions are not
- // multiples of eight. In practice, leaving those pixels white does not seem to be a problem.
+ // of the blocks around it. Also handles the corner cases (fractional blocks are computed based
+ // on the last 8 pixels in the row/column which are also used in the previous block).
private static void calculateThresholdForBlock(byte[] luminances, int subWidth, int subHeight,
- int stride, int[][] blackPoints, BitMatrix matrix) {
+ int width, int height, int[][] blackPoints, BitMatrix matrix) {
for (int y = 0; y < subHeight; y++) {
+ int yoffset = y << 3;
+ if ((yoffset + 8) >= height) {
+ yoffset = height - 8;
+ }
for (int x = 0; x < subWidth; x++) {
+ int xoffset = x << 3;
+ if ((xoffset + 8) >= width) {
+ xoffset = width - 8;
+ }
int left = (x > 1) ? x : 2;
left = (left < subWidth - 2) ? left : subWidth - 3;
int top = (y > 1) ? y : 2;
sum += blackRow[left + 2];
}
int average = sum / 25;
- threshold8x8Block(luminances, x << 3, y << 3, average, stride, matrix);
+ threshold8x8Block(luminances, xoffset, yoffset, average, width, matrix);
}
}
}
// Calculates a single black point for each 8x8 block of pixels and saves it away.
private static int[][] calculateBlackPoints(byte[] luminances, int subWidth, int subHeight,
- int stride) {
+ int width, int height) {
int[][] blackPoints = new int[subHeight][subWidth];
for (int y = 0; y < subHeight; y++) {
+ int yoffset = y << 3;
+ if ((yoffset + 8) >= height) {
+ yoffset = height - 8;
+ }
for (int x = 0; x < subWidth; x++) {
+ int xoffset = x << 3;
+ if ((xoffset + 8) >= width) {
+ xoffset = width - 8;
+ }
int sum = 0;
int min = 255;
int max = 0;
for (int yy = 0; yy < 8; yy++) {
- int offset = ((y << 3) + yy) * stride + (x << 3);
+ int offset = (yoffset + yy) * width + xoffset;
for (int xx = 0; xx < 8; xx++) {
int pixel = luminances[offset + xx] & 0xff;
sum += pixel;
// If the contrast is inadequate, use half the minimum, so that this block will be
// treated as part of the white background, but won't drag down neighboring blocks
// too much.
- int average = (max - min > 24) ? (sum >> 6) : (min >> 1);
+ int average;
+ if (max - min > 24) {
+ average = sum >> 6;
+ } else {
+ // When min == max == 0, let average be 1 so all is black
+ average = max == 0 ? 1 : min >> 1;
+ }
blackPoints[y][x] = average;
}
}