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(python2.1-lib.info)imageop

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Manipulate raw image data
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Manipulate raw image data.

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:

`error'
     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.