- Form: ROTATE source [LEFT] [RIGHT] [UD]
[PA=degrees] [BOX=b]
-
- [TRANSPOSE] [SINC]
- source
- the buffer containing the image to be rotated.
- LEFT
- rotates the image LEFT (counterclockwise).
- RIGHT
- rotates the image RIGHT (clockwise).
- UD
- turns the image upside-down.
- TRANSPOSE
- transposes the image.
- PA=degrees
- rotates the image by the specified number of degrees.
- BOX=b
- gives the size of the output image when the rotation is
specified in degrees.
- SINC
- uses 2-D sinc interpolation, rather than bilinear,
for general rotation.
This command rotates an image. The keywords LEFT, RIGHT and UD are used
for simple rotations. These operate on the entire image. The directions
LEFT or RIGHT or UD refer to the orientation of the image as seen on the
image display or in a contour map. Imagine the image drawn or a piece of paper
for these rotations. UD is the same as two LEFT or two RIGHT rotations
done in sequence. It does NOT produce the a result which can be done with
FLIP. The keyword TRANSPOSE will transpose the image, i.e. change the
columns into rows and vice versa; this is equivalent to a ROTATE LEFT plus
a FLIP ROWS or a FLIP ROWS plus a ROTATE RIGHT.
Use PA= to specify an arbitrary rotation in degrees. PA=0 is vertical as
seen on the television, with positive rotation angles corresponding to a
counterclockwise rotation. A box may be specified, in which case the whole
image will be rotated around the center of the box, then windowed to fit
into the box. The box coordinates should be specified in the ROTATED
coordinate frame, not in the original frame. If no box is specified, a box
the size and position of the whole image is assumed. Note that in this
case some corners may be cut off in the rotated image, while others may be
filled with zeros. Arbitrary rotations require interpolation to be done on
the data. The default method is bilinear interpolation, but higher accuracy
2-D sinc interpolation will be used if the SINC keyword is given.
Note that RIGHT and PA=90 (for example) are not equivalent. The RIGHT
keyword implies a simple shuffling around of the pixel values, while PA=90
will actually attempt to interpolate the values. Another difference lies
in the way the resulting image is proportioned: PA=90 will result in an
image with the same number of rows and columns as the original, but RIGHT
will result in an image with the number of rows and columns reversed.
- ROTATE 4 LEFT
- Rotates all of image 4 90 degrees
in a counter-clockwise direction.
- ROTATE 1 BOX=6 PA=145
- Rotates image 1 by 145 degrees and
keeps only the part of the rotated image which lies in box 6.