OVERRGB(1)

💖 OVERRGB(1) 💖

okay bestie, welcome to overrgb, a User Commands classic — the little tool that takes your fancy RGBA nrrd and slaps it on top of a background color (or a whole background image) like it's layering an outfit. ✨

---

🌸 NAME 🌸

overrgb — composites an RGBA nrrd over a background color (or image). that's the whole gig. and it does it beautifully. 💅

---

🎀 SYNOPSIS 🎀

overrgb -i <nin> [-c <contrast>] [-cfp <fixed point>] [-g <gamma>] [-b
<background>] [-bi <nbg>] -o <filename>

like yes, that's a lot of little flags but we're gonna go through every single one together, no skipping, no cap. 🫶

---

🦋 DESCRIPTION 🦋

so here's the vibe. overrgb composites an RGBA nrrd over a background color (or image), and then it does gamma correction, and then it quantizes to an 8-bit image. it's giving full pipeline energy. 🔥

and like, plot twist — your input nrrd can lowkey have more than 4 values per pixel, but only the first four are ever used. the rest are just standing there, decorative. 🙈

here's the part that actually matters for getting your numbers right: if the RGBA nrrd is floating point, the values are taken at face value, periodt. if it's fixed point, the values are interpreted as having been quantized — so that 8-bit RGBA images will act exactly as you expect. iykyk. 💜

and when you're compositing with a background image, the given background image does not have to be the same size as the input image. it will get resampled (with linear interpolation) to fit. she stretches to serve the look. 💖

---

✨ OPTIONS ✨

• -i <nin> — input nrrd to composite (nrrd). the main character of the whole operation. 👑
• -c <contrast> — contrast to apply to RGB values, before gamma. “0.0” means no change, “1.0” means thresholding, “-1.0” means a complete washout. (double); default: “0.0”
• -cfp <fixed point> — component level that doesn't change with contrast (double); default: “0.5”
• -g <gamma> — gamma to apply to image data, after contrast (double); default: “1.0”
• -b <background> — background color to composite against; white is 1 1 1, not 255 255 255. (3 doubles); default: “0 0 0”

not me begging you to remember 1 1 1 and not 255 255 255 😭 this is the #1 thing people get wrong and it will absolutely wreck your output. fr fr.

• -bi <nbg> — 8-bit RGB background image to composite against (nrrd); default: “”
• -o <filename> — file to write output PPM image to (string); default: “-”

---

🌈 SEE ALSO 🌈

gprobe(1), ilk(1), mrender(1), miter(1), nrrdSanity(1), puller(1), tend(1), unu(1), vprobe(1)

the whole friend group. go say hi. 🧚

---

and that's the whole page, bestie! this one's from April 2021, part of the User Commands lineup — so if you're citing her, that's the date and the manual section to credit. slay, go composite something gorgeous. 💖✨🎀🦋🌸💅🫶