The imageop module contains some useful operations on images.
It operates on images consisting of 8 or 32 bit pixels stored in
Python strings. This is the same format as used by
gl.lrectwrite() and the imgfile module.
The module defines the following variables and functions:
exceptionerror
This exception is raised on all errors, such as unknown number of bits
per pixel, etc.
crop(
image, psize, width, height, x0, y0, x1, y1)
Return the selected part of image, which should by
width by height in size and consist of pixels of
psize bytes. x0, y0, x1 and y1 are like
the gl.lrectread() parameters, i.e. the boundary is
included in the new image. The new boundaries need not be inside the
picture. Pixels that fall outside the old image will have their value
set to zero. If x0 is bigger than x1 the new image is
mirrored. The same holds for the y coordinates.
scale(
image, psize, width, height, newwidth, newheight)
Return image scaled to size newwidth by newheight.
No interpolation is done, scaling is done by simple-minded pixel
duplication or removal. Therefore, computer-generated images or
dithered images will not look nice after scaling.
tovideo(
image, psize, width, height)
Run a vertical low-pass filter over an image. It does so by computing
each destination pixel as the average of two vertically-aligned source
pixels. The main use of this routine is to forestall excessive
flicker if the image is displayed on a video device that uses
interlacing, hence the name.
grey2mono(
image, width, height, threshold)
Convert a 8-bit deep greyscale image to a 1-bit deep image by
thresholding all the pixels. The resulting image is tightly packed and
is probably only useful as an argument to mono2grey().
dither2mono(
image, width, height)
Convert an 8-bit greyscale image to a 1-bit monochrome image using a
(simple-minded) dithering algorithm.
mono2grey(
image, width, height, p0, p1)
Convert a 1-bit monochrome image to an 8 bit greyscale or color image.
All pixels that are zero-valued on input get value p0 on output
and all one-value input pixels get value p1 on output. To
convert a monochrome black-and-white image to greyscale pass the
values 0 and 255 respectively.
grey2grey4(
image, width, height)
Convert an 8-bit greyscale image to a 4-bit greyscale image without
dithering.
grey2grey2(
image, width, height)
Convert an 8-bit greyscale image to a 2-bit greyscale image without
dithering.
dither2grey2(
image, width, height)
Convert an 8-bit greyscale image to a 2-bit greyscale image with
dithering. As for dither2mono(), the dithering algorithm
is currently very simple.
grey42grey(
image, width, height)
Convert a 4-bit greyscale image to an 8-bit greyscale image.
grey22grey(
image, width, height)
Convert a 2-bit greyscale image to an 8-bit greyscale image.
backward_compatible
If set to 0, the functions in this module use a non-backward
compatible way of representing multi-byte pixels on little-endian
systems. The SGI for which this module was originally written is a
big-endian system, so setting this variable will have no effect.
However, the code wasn't originally intended to run on anything else,
so it made assumptions about byte order which are not universal.
Setting this variable to 0 will cause the byte order to be reversed on
little-endian systems, so that it then is the same as on big-endian
systems.
