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Fixed up some comments and formatting.

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git-svn-id: https://zxing.googlecode.com/svn/trunk@1979 59b500cc-1b3d-0410-9834-0bbf25fbcc57
This commit is contained in:
dswitkin@google.com 2011-10-18 19:17:33 +00:00
parent 4dfe5d7828
commit f74e806694
1 changed files with 32 additions and 54 deletions
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86
core/src/com/google/zxing/common/HybridBinarizer.java
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@ -75,7 +75,8 @@ public final class HybridBinarizer extends GlobalHistogramBinarizer {
int[][] blackPoints = calculateBlackPoints(luminances, subWidth, subHeight, width, height);
BitMatrix newMatrix = new BitMatrix(width, height);
calculateThresholdForBlock(luminances, subWidth, subHeight, width, height, blackPoints, newMatrix);
calculateThresholdForBlock(luminances, subWidth, subHeight, width, height, blackPoints,
newMatrix);
matrix = newMatrix;
} else {
// If the image is too small, fall back to the global histogram approach.
@ -91,13 +92,8 @@ public final class HybridBinarizer extends GlobalHistogramBinarizer {
// 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 (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 width,
int height,
int[][] blackPoints,
BitMatrix matrix) {
private static void calculateThresholdForBlock(byte[] luminances, int subWidth, int subHeight,
int width, int height, int[][] blackPoints, BitMatrix matrix) {
for (int y = 0; y < subHeight; y++) {
int yoffset = y << BLOCK_SIZE_POWER;
if ((yoffset + BLOCK_SIZE) >= height) {
@ -115,7 +111,8 @@ public final class HybridBinarizer extends GlobalHistogramBinarizer {
int sum = 0;
for (int z = -2; z <= 2; z++) {
int[] blackRow = blackPoints[top + z];
sum += blackRow[left - 2] + blackRow[left - 1] + blackRow[left] + blackRow[left + 1] + blackRow[left + 2];
sum += blackRow[left - 2] + blackRow[left - 1] + blackRow[left] + blackRow[left + 1] +
blackRow[left + 2];
}
int average = sum / 25;
threshold8x8Block(luminances, xoffset, yoffset, average, width, matrix);
@ -124,15 +121,11 @@ public final class HybridBinarizer extends GlobalHistogramBinarizer {
}
// Applies a single threshold to an 8x8 block of pixels.
private static void threshold8x8Block(byte[] luminances,
int xoffset,
int yoffset,
int threshold,
int stride,
BitMatrix matrix) {
private static void threshold8x8Block(byte[] luminances, int xoffset, int yoffset, int threshold,
int stride, BitMatrix matrix) {
for (int y = 0, offset = yoffset * stride + xoffset; y < BLOCK_SIZE; y++, offset += stride) {
for (int x = 0; x < BLOCK_SIZE; x++) {
// Comparison needs to be <= so that black == 0 pixels are black even if the threshold is 0
// Comparison needs to be <= so that black == 0 pixels are black even if the threshold is 0.
if ((luminances[offset + x] & 0xFF) <= threshold) {
matrix.set(xoffset + x, yoffset + y);
}
@ -140,19 +133,11 @@ public final class HybridBinarizer extends GlobalHistogramBinarizer {
}
}
// Esimates blackPoint from previously calculated neighbor esitmates
private static int getBlackPointFromNeighbors(int[][] blackPoints, int x, int y) {
return (blackPoints[y-1][x] +
2*blackPoints[y][x-1] +
blackPoints[y-1][x-1]) >> 2;
}
// 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 width,
int height) {
// See the following thread for a discussion of this algorithm:
// http://groups.google.com/group/zxing/browse_thread/thread/d06efa2c35a7ddc0
private static int[][] calculateBlackPoints(byte[] luminances, int subWidth, int subHeight,
int width, int height) {
int[][] blackPoints = new int[subHeight][subWidth];
for (int y = 0; y < subHeight; y++) {
int yoffset = y << BLOCK_SIZE_POWER;
@ -180,36 +165,29 @@ public final class HybridBinarizer extends GlobalHistogramBinarizer {
}
}
// See
// http://groups.google.com/group/zxing/browse_thread/thread/d06efa2c35a7ddc0
// The default estimate is the average of the values in the block
// The default estimate is the average of the values in the block.
int average = sum >> 6;
if (max - min <= 24) {
// If variation wihthin the block is low, assume this is a
// block with only light or only dark pixels.
// The default assumption is that the block is light/background.
// Since no estimate for the level of dark pixels
// exists locally, use half the min for the block.
// If variation within the block is low, assume this is a block with only light or only
// dark pixels. In that case we do not want to use the average, as it would divide this
// low contrast area into black and white pixels, essentially creating data out of noise.
//
// The default assumption is that the block is light/background. Since no estimate for
// the level of dark pixels exists locally, use half the min for the block.
average = min >> 1;
if (y > 0 && x > 0) {
// Correct the "white/background" assumption for blocks
// that have neighbors by comparing the pixels in this
// block to the previously calculated blackpoints. This is
// based on the fact that dark barcode symbology is always
// surrounded by some amount of light background for which
// reasonable blackpoint esimates were made. The bp estimated
// at the bondaries is used for the interior.
// The (min < bp) seems pretty arbitrary but works better than
// other heurstics that were tried.
int bp = getBlackPointFromNeighbors(blackPoints, x, y);
if (min < bp) {
average = bp;
if (y > 0 && x > 0) {
// Correct the "white background" assumption for blocks that have neighbors by comparing
// the pixels in this block to the previously calculated black points. This is based on
// the fact that dark barcode symbology is always surrounded by some amount of light
// background for which reasonable black point estimates were made. The bp estimated at
// the boundaries is used for the interior.
// The (min < bp) is arbitrary but works better than other heuristics that were tried.
int averageNeighborBlackPoint = (blackPoints[y - 1][x] + (2 * blackPoints[y][x - 1]) +
blackPoints[y - 1][x - 1]) >> 2;
if (min < averageNeighborBlackPoint) {
average = averageNeighborBlackPoint;
}
}
}