21.2. imageop — Manipulate raw image data
Deprecated since version 2.6: The imageop module has been removed in Python 3.0.
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:
- This exception is raised on all errors, such as unknown number of bits per
imageop.crop(image, psize, width, height, x0, y0, x1, y1)
- Return the selected part of image, which should be 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.
imageop.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.
imageop.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.
imageop.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().
imageop.dither2mono(image, width, height)
- Convert an 8-bit greyscale image to a 1-bit monochrome image using a
(simple-minded) dithering algorithm.
imageop.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.
imageop.grey2grey4(image, width, height)
- Convert an 8-bit greyscale image to a 4-bit greyscale image without dithering.
imageop.grey2grey2(image, width, height)
- Convert an 8-bit greyscale image to a 2-bit greyscale image without dithering.
imageop.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.
imageop.grey42grey(image, width, height)
- Convert a 4-bit greyscale image to an 8-bit greyscale image.
imageop.grey22grey(image, width, height)
- Convert a 2-bit greyscale image to an 8-bit greyscale image.
- 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.