com.google.zxing.common
Class GridSampler

java.lang.Object
  extended by com.google.zxing.common.GridSampler
Direct Known Subclasses:
DefaultGridSampler

public abstract class GridSampler
extends Object

Implementations of this class can, given locations of finder patterns for a QR code in an image, sample the right points in the image to reconstruct the QR code, accounting for perspective distortion. It is abstracted since it is relatively expensive and should be allowed to take advantage of platform-specific optimized implementations, like Sun's Java Advanced Imaging library, but which may not be available in other environments such as J2ME, and vice versa. The implementation used can be controlled by calling GridSampler.setGridSampler(GridSampler) with an instance of a class which implements this interface.

Since:
BlackBerry API 6.0.0

Constructor Summary
GridSampler()
           
 
Method Summary
protected static void checkAndNudgePoints(BitMatrix image, float[] points)
          Checks a set of points that have been transformed to sample points on an image against the image's dimensions to see if the point are even within the image.
static GridSampler getInstance()
           
abstract  BitMatrix sampleGrid(BitMatrix image, int dimension, float p1ToX, float p1ToY, float p2ToX, float p2ToY, float p3ToX, float p3ToY, float p4ToX, float p4ToY, float p1FromX, float p1FromY, float p2FromX, float p2FromY, float p3FromX, float p3FromY, float p4FromX, float p4FromY)
          Samples an image for a square matrix of bits of the given dimension.
static void setGridSampler(GridSampler newGridSampler)
          Sets the implementation of GridSampler used by the library.
 
Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 



Constructor Detail

GridSampler

public GridSampler()
Since:
BlackBerry API 6.0.0


Method Detail

setGridSampler

public static void setGridSampler(GridSampler newGridSampler)
Sets the implementation of GridSampler used by the library. One global instance is stored, which may sound problematic. But, the implementation provided ought to be appropriate for the entire platform, and all uses of this library in the whole lifetime of the JVM. For instance, an Android activity can swap in an implementation that takes advantage of native platform libraries.

Parameters:
newGridSampler - The platform-specific object to install.
Since:
BlackBerry API 6.0.0

getInstance

public static GridSampler getInstance()
Returns:
the current implementation of GridSampler
Since:
BlackBerry API 6.0.0

sampleGrid

public abstract BitMatrix sampleGrid(BitMatrix image,
                                     int dimension,
                                     float p1ToX,
                                     float p1ToY,
                                     float p2ToX,
                                     float p2ToY,
                                     float p3ToX,
                                     float p3ToY,
                                     float p4ToX,
                                     float p4ToY,
                                     float p1FromX,
                                     float p1FromY,
                                     float p2FromX,
                                     float p2FromY,
                                     float p3FromX,
                                     float p3FromY,
                                     float p4FromX,
                                     float p4FromY)
                              throws ReaderException

Samples an image for a square matrix of bits of the given dimension. This is used to extract the black/white modules of a 2D barcode like a QR Code found in an image. Because this barcode may be rotated or perspective-distorted, the caller supplies four points in the source image that define known points in the barcode, so that the image may be sampled appropriately.

The last eight "from" parameters are four X/Y coordinate pairs of locations of points in the image that define some significant points in the image to be sample. For example, these may be the location of finder pattern in a QR Code.

The first eight "to" parameters are four X/Y coordinate pairs measured in the destination BitMatrix, from the top left, where the known points in the image given by the "from" parameters map to.

These 16 parameters define the transformation needed to sample the image.

Parameters:
image - image to sample
dimension - width/height of BitMatrix to sample from image
Returns:
BitMatrix representing a grid of points sampled from the image within a region defined by the "from" parameters
Throws:
ReaderException - if image can't be sampled, for example, if the transformation defined by the given points is invalid or results in sampling outside the image boundaries
Since:
BlackBerry API 6.0.0

checkAndNudgePoints

protected static void checkAndNudgePoints(BitMatrix image,
                                          float[] points)
                                   throws ReaderException

Checks a set of points that have been transformed to sample points on an image against the image's dimensions to see if the point are even within the image.

This method will actually "nudge" the endpoints back onto the image if they are found to be barely (less than 1 pixel) off the image. This accounts for imperfect detection of finder patterns in an image where the QR Code runs all the way to the image border.

For efficiency, the method will check points from either end of the line until one is found to be within the image. Because the set of points are assumed to be linear, this is valid.

Parameters:
image - image into which the points should map
points - actual points in x1,y1,...,xn,yn form
Throws:
ReaderException - if an endpoint is lies outside the image boundaries
Since:
BlackBerry API 6.0.0





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