Looking at RGB to MONO? Here's why MONO isn't a standard "save as" target — and what to use.
MONO isn't a normal image format — it's a headerless raw pixel buffer, so there's no meaningful "convert RGB to MONO".
A MONO file is just a stream of raw pixel values (one-bit black-and-white samples) with no width, height or color information stored inside. Anything opening it has to be told the exact dimensions and layout separately — so it isn't a portable image you can simply convert to.
For an image you can actually open and share, pick a standard format that stores its own dimensions and color — PNG, JPG or TIFF.
RGB is Silicon Graphics' image format from SGI Unix workstations, storing uncompressed or RLE-compressed color used in early 3D and film work.
How to open RGB opens in GIMP, ImageMagick and SGI-era tools; convert to PNG/TIFF for modern editors.
Full RGB format guideMONO (Raw Monochrome Bits) is a raster image format developed by Various around 1980s. It's a specialised format — converting to a mainstream format like JPG or PNG makes it easy to open and share anywhere.
How to open MONO files open in specialised software and some professional tools; for everyday use, convert MONO to JPG or PNG.
Full MONO format guide