88 lines
3.5 KiB
TeX
88 lines
3.5 KiB
TeX
\section{Built-in module \sectcode{imageop}}
|
|
\bimodindex{imageop}
|
|
|
|
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 \code{gl.lrectwrite} and the \code{imgfile} module.
|
|
|
|
The module defines the following variables and functions:
|
|
|
|
\renewcommand{\indexsubitem}{(in module imageop)}
|
|
|
|
\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}
|
|
This function takes the image in \code{image}, which should by
|
|
\code{width} by \code{height} in size and consist of pixels of
|
|
\code{psize} bytes, and returns the selected part of that image. \code{X0},
|
|
\code{y0}, \code{x1} and \code{y1} are like the \code{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 \code{x0} is bigger than \code{x1} the new image is mirrored. The
|
|
same holds for the y coordinates.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{scale}{image\, psize\, width\, height\, newwidth\, newheight}
|
|
This function returns a \code{image} scaled to size \code{newwidth} by
|
|
\code{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}
|
|
This function runs 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}
|
|
This function converts a 8-bit deep greyscale image to a 1-bit deep
|
|
image by tresholding all the pixels. The resulting image is tightly
|
|
packed and is probably only useful as an argument to \code{mono2grey}.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{dither2mono}{image\, width\, height}
|
|
This function also converts an 8-bit greyscale image to a 1-bit
|
|
monochrome image but it uses a (simple-minded) dithering algorithm.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{mono2grey}{image\, width\, height\, p0\, p1}
|
|
This function converts a 1-bit monochrome image to an 8 bit greyscale
|
|
or color image. All pixels that are zero-valued on input get value
|
|
\code{p0} on output and all one-value input pixels get value \code{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 \code{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}
|