i.his.rgb(1)

📦
version 8.4.2 · 8 versions
, in fedora 44

💖 i.his.rgb — the GRASS GIS glow-up page 💖

okay bestie, sit down, hydrate, because we're about to take three raster maps living in HIS (Hue-Intensity-Saturation) color space and transform them into RGB (Red-Green-Blue) color space. it's giving alchemy but it's just math. this is i.his.rgb(1) from the GRASS GIS User's Manual and she is iconic.

✨ NAME ✨

i.his.rgb — Transforms raster maps from HIS (Hue-Intensity-Saturation) color space to RGB (Red-Green-Blue) color space. no cap, that's the whole job. 🎀

🏷️ KEYWORDS 🏷️

imagery, color transformation, RGB, HIS, IHS

🦋 SYNOPSIS 🦋

i.his.rgb
i.his.rgb --help
i.his.rgb hue=name intensity=name saturation=name red=name green=name
blue=name  [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

💅 FLAGS 💅

  • --overwrite — let those output files bulldoze any existing files in their way. permission to overwrite: granted. 💥
  • --help — prints the usage summary, aka the little cheat sheet.
  • --verbose — verbose module output. she talks more. we love a chatty queen. 🗣️
  • --quiet — quiet module output. she says nothing. mysterious. ✨
  • --ui — force launching the GUI dialog. mouse girlies, this one's for you. 🖱️

🧚 PARAMETERS 🧚

  • hue=name [required] — name of input raster map (hue).
  • intensity=name [required] — name of input raster map (intensity).
  • saturation=name [required] — name of input raster map (saturation).
  • red=name [required] — name for output raster map (red).
  • green=name [required] — name for output raster map (green).
  • blue=name [required] — name for output raster map (blue).
bestie these are all required. every single one. no skipping. the module will simply not play with you. 🙈

🌸 DESCRIPTION 🌸

so i.his.rgb is an image processing program, right? you hand it three input raster map layers and it treats them as the hue, intensity and saturation components. then it hands you back three output raster map layers representing the red, green and blue components of that same data. it's a whole transformation arc. 👑

the output raster map layers get created by a standard hue-intensity-saturation (HIS) to red-green-blue (RGB) color transformation. that's the vibe.

and each output raster map layer is given a linear gray scale color table. so they start out monochrome and humble. 💅

also important: the current geographic region and mask settings are respected. she respects boundaries. as she should. 🫶

😭 NOTES 😭

okay this is the part where I have to be real with you.

It is not possible to process three bands with i.his.rgb and then exactly recover the original bands with i.rgb.his.

why?? because of loss of precision from integer computations and rounding. it's not a bug, it's just numbers being numbers. 💀

but wait, it's not all doom. tests have shown that more than 70% of the original cell values will be reproduced exactly after transformation in both directions, and 99% will be within plus or minus 1. so like, mostly fine. mostly.

however — and this is the part that keeps me up at night — a few cell values may differ significantly from their original values. so. yeah. round-tripping is not a perfect circle. it's more of a wobbly oval. 🌀

👀 SEE ALSO 👀

  • i.rgb.his
  • r.colors

the girlies you should also be reading. iykyk. 📚

👑 AUTHOR 👑

David Satnik, GIS Laboratory, Central Washington University

with acknowledgements to Ali Vali, Univ. of Texas Space Research Center, for the core routine.

shoutout to the core routine. the backbone. the moment. 🔥

💜 SOURCE CODE 💜

Available at: i.his.rgb source code (history)

Accessed: Saturday Jan 17 05:41:41 2026

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© 2003-2025 GRASS Development Team, GRASS GIS 8.4.2 Reference Manual

okay that's the whole page, bestie!! go forth and transform your rasters, respect your region and mask settings, and remember — a few cell values may differ significantly, and honestly? same. 😌

GRASS 8.4.2 — i.his.rgb(1) — signing off, mwah 💋✨🦋

📦 where this page comes from