fb-png — save a framebuffer image in a color Portable Network Graphics (PNG) file


fb-png [-ic ] [-# nbytes/pixel] [-g gamma] [-F framebuffer] [-s squaresize] [-w width] [-n height] [file.png]


fb-png will take a region of a framebuffer display and save it as a color png format file. The environment variable FB_FILE is used to select the display device (see brlcad(1)). If this variable is not set, the default device for your system will be used. Alternatively, the framebuffer may be explicitly specified by using the -F flag.

By default, the output png file, and the requested framebuffer size, is assumed to be 512x512 pixels. The -s flag will set both the file height and width to be the given size, while -w and -n are used for setting them individually.

A first quadrant coordinate system is used (origin in lower left of screen), and the area saved is normally from this origin. The -i flag switches to a fourth quadrant system, both in the storage order as well as the origin offset coordinates (i.e. origin is now the upper left corner of the screen).

The -# nbytes/pixel flag specifies the number of bytes per pixel. The only values accepted are 1 and 3.

The -c flag specifies that the color map in the frame buffer should be applied to the pixel values (crunched) before they are written to the output file.

The -g gamma flag sets the specified gamma correction value into the created PNG file. A value of 0.6 is a close approximation of PC display monitors. A negative gamma value disables writing a gAMA chunk out entirely (and is the default).


brlcad(1), png-fb(1), fb-bw(1), pix(5)


John R. Anderson


This software is Copyright (c) 1998-2016 by the United States Government as represented by U.S. Army Research Laboratory.


Reports of bugs or problems should be submitted via electronic mail to <>.