Vgrid is a virtual grid program for radiology that enhances the contrast of radiographs by means of the algorithm Adaptive Windowing (AW).

Adaptive Windowing is based exclusively on linear transformations of pixel values so that the contrast in the neighborhood of each pixel is expanded until it fills the full range of values available. The effect is similar to passing a "contrast magnifier" over the image.

The results obtained with the AW algorithm improve the contrast of the images without introducing artefacts, facilitating the visual interpretation of chest radiographic findings.

The AW algorithm has been developed as part of the master's thesis of a master's degree in Medical Physics (UNED).


Vgrid is a command line tool. Vgrid reads images in PNG greyscale or RGB format and saves images in PNG greyscale format using by default the same bit depth as the input image. Vgrid accepts images with a bit depth of 8 or 16 bits.

If no file names are specified, vgrid reads an image from standard input and writes the result to standard output.


The manual is available in the info system of the GNU Operating System. Use info to access the top level info page. Use info vgrid to access the vgrid section directly.

An online manual for vgrid can be found at manual/vgrid_manual.html.


The latest released version of vgrid can be found at You may also subscribe to vgrid-bug and receive an email every time a new version is released.

You may compile and optionally install vgrid by running the following commands:

tar -xf vgrid[version].tar.lz
cd vgrid[version] && ./configure && make check

then (as root) type:

make install

How to get help

For general discussion of bugs in vgrid the mailing list is the most appropriate forum. Please send messages as plain text. Please do not send messages encoded as HTML nor encoded as base64 MIME nor included as multiple formats. Please include a descriptive subject line. If all of the subject are "bug in vgrid" it is impossible to differentiate them.

An archive of the bug report mailing list is available at

How to help

To contact the author, either to report a bug or to contribute fixes or improvements, send mail to Please send messages as plain text. If posting patches they should be in unified diff format against the latest version. They should include a text description.

See also the vgrid project page at Savannah.


Vgrid is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 2 of the License, or (at your option) any later version.

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Copyright © 2021 Sonia Diaz Pacheco

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Updated: 2021-07-24

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