# cpython-withatomic / Doc / libimageop.tex

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  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 \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}