[Gimp-user] 8 and 1 bit images

[rich404 <forums gimpusers com>]

> The mask files needed are exactly what you state - the 'white' area is
> 'transparent' so when the original image (actually a satellite image
> of an area in the world) is 'compiled' together with the mask file the
> black area is interpreted as that part of the original image you want
> NOT included and the white area allows the corresponding area of the
> original image to 'show through'.
> I have attached the original satellite image and the 'water mask'. The
> black area in the water mask will result in all that part of the
> original satellite image being masked OUT and the white area will
> allow that part of the original satellite image to show through.
> Hope I have explained properly.
> Apart from an obvious smaller TIFF file (1 bit) it apparently results
> in the compiled image file (a file type BGL which is used with Flight
> Simulator) also being smaller.
> I guess it's just to make smaller files.
> I must get back to the 'scenery forum' and ask some questions.

looking at this

http://www.fsdeveloper.com/forum/threads/bland-mask-water-mask-how-to.18894/ it
says

"quote" ...is the watermask. This gives water characteristics to any black area.
The mask is an 8-bit tif using only black and white

So that is all you need. A grayscale image. If your image has transparency (an
alpha channel) remove it

Layer -> Transparency -> Remove Alpha Channel

export as as a tif

-- 
rich404 (via www.gimpusers.com/forums)