FB-PNG(1)

📦
version 7.44.0 · 2 versions
, in nixpkgs unstable

💾 fb-png — the NAME bit 💅

okay so bestie, fb-png saves a framebuffer image as a Portable Network Graphics (PNG) file. that's the whole vibe. ✨

🌸 SYNOPSIS 🌸

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

🎀 DESCRIPTION 🎀

so fb-png literally reads a region of a framebuffer and saves it as a PNG (Portable Network Graphics) file. that's it, that's the girlboss move. 💖 if you don't hand it an output file name, the data goes straight to standard output. no drama.

by default the region it reads is 512x512 pixels, in first-quadrant order (origin at the lower left, iykyk). wanna change the size? that's what -s, -w, and -n are for, bestie. and if the open framebuffer is smaller than the size you asked for? no worries — the region gets trimmed to fit. 🫶

cute lil note: use png-fb(1) to display a PNG file in a framebuffer. the reverse slay.

✨ OPTIONS ✨

  • -i — reads the framebuffer bottom-to-top, inverting the image vertically (fourth-quadrant order, origin at the upper left). flip it, reverse it, iconic. 🔄
  • -c — applies ("crunches") the framebuffer color map to pixel values before writing. if the framebuffer has no map, or has a linear one, this one just gets ignored. 🙈
  • -# nbytes/pixel — number of bytes per pixel: 1 for grayscale or 3 for color (color is the default, obvi 💅).
  • -F framebuffer — specify the framebuffer device. defaults to the FB_FILE environment variable (peep brlcad(1) for the tea ☕).
  • -g gamma — writes the specified gamma correction value into the PNG gAMA chunk. a value of 0.6 approximates PC display monitors. a non-positive value (the default is -1.0) disables writing the gAMA chunk entirely. so like, -1.0 = no gAMA chunk, at all, periodt.
  • -s squaresize — sets both width and height to squaresize pixels (default 512). symmetrical queen. 👑
  • -w width — sets the width in pixels (default 512).
  • -n height — sets the height in pixels (default 512).
  • -h, -? — prints a usage message and exits. the classic "help me help you" moment 😭

🔥 EXAMPLES 🔥

Example 1. Render a model and capture the framebuffer to PNG

rt -s 1024 -F /dev/X moss.g all.g &
fb-png -F /dev/X -s 1024 moss.png

ray traces the moss.g model into a 1024x1024 X11 framebuffer with rt(1), then grabs that framebuffer and saves it as a PNG image of the exact same size. matching the -s size to the framebuffer is the whole trick — it ensures the entire image gets captured. no crumbs left behind. 🍓

Example 2. Save the lower-left quadrant of the default framebuffer

fb-png -w 256 -n 256 crop.png

reads only a 256x256 region (anchored at the origin) from the framebuffer named by the FB_FILE environment variable, and writes it to crop.png. tiny, precious, a lil snack. 🧚

🦋 SEE ALSO 🦋

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

💜 AUTHOR 💜

BRL-CAD Team — legends, honestly.

This software is Copyright (c) 1998-2026 by the United States Government as represented by U.S. Army Research Laboratory. (yes, the whole range, 1998 all the way to 2026, fr fr.)

⭐ BUG REPORTS ⭐

Reports of bugs or problems should be submitted via electronic mail to devs@brlcad.org. tell 'em you sent the bugs, not the vibes 💀

anyway that's the whole page bestie — brought to you by the BRL-CAD girlies, FB-PNG(1) energy, dated somewhere in the 1998-2026 copyright era. now go capture that framebuffer, you absolute main character. 💅✨🎀

📦 where this page comes from