Provides static methods to rotate (in steps of 90 degrees), flip and mirror array elements.
The image data is expected to be available as an array of integer values, being stored as rows top-to-bottom.
Within each row, the data is laid out from left to right.
This class may also been useful for transposing matrices.
The rotation by 90 and 270 degrees in-place (i.e., without using a
second array to copy to) is based on ideas and code developed
by others.
See
Rotation of arrays
by Thomas W. Christopher.
I also got very useful advice from Hans-Bernhard Broeker and others in
comp.graphics.algorithms.
There is a thread titled
In-place rotation of pixel images starting Oct 11, 2000.
Note: This class should be adjusted if Java ever supports genericity.
Then rotation functionality could be provided for all kinds of arrays.
checkPixelArray
public static void checkPixelArray(int[] pixels,
int width,
int height)
This method checks several properties of the arguments.
If any of the properties is not fulfilled, an explaining
java.lang.IllegalArgumentException
is thrown.
Otherwise, nothing happens.
This method is supposed to be called at the beginning of several
other methods in this class.
Properties checked:
pixels
is non-nullwidth
and height
are larger than zero- number of elements in
pixels
is at least width
times height
flip
public static final int[] flip(boolean inPlace,
int[] pixels,
int width,
int height)
Flips the image given by the arguments.
The inPlace argument determines if the pixels array is modified or not.
If inPlace is true, no additional array is allocated.
Otherwise, an array of width times height items is allocated and the
flipped image will be stored in this array.
inPlace
- if true
all work is done on the pixels
array;
otherwise, a second array is allocated and the pixels
array
remains unmodifiedpixels
- the array of pixels that form the image to be flippedwidth
- the horizontal resolution of the image; must be larger than 0height
- the vertical resolution of the image; must be larger than 0
- the flipped image as int array; equals
pixels
if
inPlace
is true
flip
private static final int[] flip(int[] pixels,
int width,
int height)
flipInPlace
private static final void flipInPlace(int[] pixels,
int width,
int height)
Flips the argument image, i.e., the top line becomes the bottom line
and vice versa, etc.
This method first checks the validity of the arguments that define the image
by a call to checkPixelArray
.
Then the image data is flipped in place, no additional memory is required.
Note that after applying this operation twice you will get the original
image back.
pixels
- the array of pixels that form the image to be flippedwidth
- the horizontal resolution of the image; must be larger than 0height
- the vertical resolution of the image; must be larger than 0
rotate180
public static int[] rotate180(boolean inPlace,
int[] pixels,
int width,
int height)
Rotates the argument image by 180 degrees.
The resulting image will have exactly the same pixel resolution.
Note that this operation is the same as two consecutive 90 degree
rotations in the same direction.
Another way of implementing a 180 degree rotation is first flipping
and then mirroring the original image (or vice versa).
If
inPlace
is true, the rotation is done on the
argument
pixels
array.
Otherwise a new array of sufficient length is allocated and the
rotated image will be stored in this new array, not modifying the
content of the
pixels
array.
inPlace
- determines whether the rotated image is written to the argument arraypixels
- the array of pixels that form the image to be rotatedwidth
- the horizontal resolution of the image; must be larger than 0height
- the vertical resolution of the image; must be larger than 0
- the flipped image as int array; equals
pixels
if
inPlace
is true
rotate180
public static void rotate180(int width,
int height,
byte[] src,
int srcOffset,
byte[] dest,
int destOffset)
rotate90Left
public static void rotate90Left(int width,
int height,
byte[] src,
int srcOffset,
byte[] dest,
int destOffset)
rotate90Right
public static int[] rotate90Right(boolean inPlace,
int[] pixels,
int width,
int height)
rotate90Right
public static void rotate90Right(int width,
int height,
byte[] src,
int srcOffset,
byte[] dest,
int destOffset)
rotate90Right
private static int[] rotate90Right(int[] pixels,
int width,
int height)
rotateInPlace180
private static void rotateInPlace180(int[] pixels,
int width,
int height)
rotateInPlace90Right
private static void rotateInPlace90Right(int[] pixels,
int width,
int height)