# 18.11 `imgfile` -- Support for SGI imglib files

Availability: IRIX.

The `imgfile` module allows Python programs to access SGI imglib image files (also known as .rgb files). The module is far from complete, but is provided anyway since the functionality that there is is enough in some cases. Currently, colormap files are not supported.

The module defines the following variables and functions:

`error`
  This exception is raised on all errors, such as unsupported file type, etc.

`getsizes` (file)
  This function returns a tuple `(x, y, z)` where x and y are the size of the image in pixels and z is the number of bytes per pixel. Only 3 byte RGB pixels and 1 byte greyscale pixels are currently supported.

`read` (file)
  This function reads and decodes the image on the specified file, and returns it as a Python string. The string has either 1 byte greyscale pixels or 4 byte RGBA pixels. The bottom left pixel is the first in the string. This format is suitable to pass to `gl.lrectwrite()`, for instance.

`readscaled` (file, x, y, filter[, blur])
  This function is identical to read but it returns an image that is scaled to the given x and y sizes. If the filter and blur parameters are omitted scaling is done by simply dropping or duplicating pixels, so the result will be less than perfect, especially for computer-generated images.

  Alternatively, you can specify a filter to use to smoothen the image after scaling. The filter forms supported are `'impulse'`, `'box'`, `'triangle'`, `'quadratic'` and `'gaussian'`. If a filter is specified blur is an optional parameter specifying the blurriness of the filter. It defaults to `1.0`.

  `readscaled()` makes no attempt to keep the aspect ratio correct, so that is the users' responsibility.

`ttob` (flag)
  This function sets a global flag which defines whether the scan lines of the image are read or written from bottom to top (flag is zero, compatible with SGI GL) or from top to bottom(flag is one, compatible with X). The default is zero.

`write` (file, data, x, y, z)
  This function writes the RGB or greyscale data in data to image file file. x and y give the size of the image, z is 1 for 1 byte greyscale images or 3 for RGB images (which are stored as 4 byte values of which only the lower three bytes are used). These are the formats returned by `gl.lrectread()`.