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-\section{\module{imageop} ---
- Manipulate raw image data}
-
-\declaremodule{builtin}{imageop}
-\modulesynopsis{Manipulate raw image data.}
-
-
-The \module{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
-\function{gl.lrectwrite()} and the \refmodule{imgfile} module.
-
-The module defines the following variables and functions:
-
-\begin{excdesc}{error}
-This exception is raised on all errors, such as unknown number of bits
-per pixel, etc.
-\end{excdesc}
-
-
-\begin{funcdesc}{crop}{image, psize, width, height, x0, y0, x1, y1}
-Return the selected part of \var{image}, which should be
-\var{width} by \var{height} in size and consist of pixels of
-\var{psize} bytes. \var{x0}, \var{y0}, \var{x1} and \var{y1} are like
-the \function{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 \var{x0} is bigger than \var{x1} the new image is
-mirrored. The same holds for the y coordinates.
-\end{funcdesc}
-
-\begin{funcdesc}{scale}{image, psize, width, height, newwidth, newheight}
-Return \var{image} scaled to size \var{newwidth} by \var{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.
-\end{funcdesc}
-
-\begin{funcdesc}{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.
-\end{funcdesc}
-
-\begin{funcdesc}{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 \function{mono2grey()}.
-\end{funcdesc}
-
-\begin{funcdesc}{dither2mono}{image, width, height}
-Convert an 8-bit greyscale image to a 1-bit monochrome image using a
-(simple-minded) dithering algorithm.
-\end{funcdesc}
-
-\begin{funcdesc}{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 \var{p0} on output
-and all one-value input pixels get value \var{p1} on output. To
-convert a monochrome black-and-white image to greyscale pass the
-values \code{0} and \code{255} respectively.
-\end{funcdesc}
-
-\begin{funcdesc}{grey2grey4}{image, width, height}
-Convert an 8-bit greyscale image to a 4-bit greyscale image without
-dithering.
-\end{funcdesc}
-
-\begin{funcdesc}{grey2grey2}{image, width, height}
-Convert an 8-bit greyscale image to a 2-bit greyscale image without
-dithering.
-\end{funcdesc}
-
-\begin{funcdesc}{dither2grey2}{image, width, height}
-Convert an 8-bit greyscale image to a 2-bit greyscale image with
-dithering. As for \function{dither2mono()}, the dithering algorithm
-is currently very simple.
-\end{funcdesc}
-
-\begin{funcdesc}{grey42grey}{image, width, height}
-Convert a 4-bit greyscale image to an 8-bit greyscale image.
-\end{funcdesc}
-
-\begin{funcdesc}{grey22grey}{image, width, height}
-Convert a 2-bit greyscale image to an 8-bit greyscale image.
-\end{funcdesc}
-
-\begin{datadesc}{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.
-\end{datadesc}