Re: IIgs finder image

[dempson@actrix.gen.nz (David Empson)]

don <don@schrank.us> wrote:

> Hello,  could one of you nice people tell me what size and color depth an
> SHR needs to be to be correctly displayed as a background image?

The Finder (along with most IIgs toolbox applications) runs in 640x200
Super Hi-res mode, so that is the mode you need to use when planning
details like colours.

I'm not sure whether Finder will insist on using the standard palette -
it probably does, because otherwise all icons will be the wrong colours.

640 mode uses dithering to generate colours. With the standard palette
there are only six real colours (black, white, red, green, yellow and
blue). All the pixels can be black or white, but only two of the colours
can be selected for each pixel. The colours are fully saturated.

I'm not sure exactly which pairs of colours go together (my IIgs RGB
monitor died about 16 years ago, and my memory is a little hazy).

My memory suggests that one column can be (black, red, green, white)
while the other can be (black, blue, yellow, white).

That would give the following dithered pairs:

black, black = black
black, blue = dark blue
black, yellow = dark yellow
black, white = grey
red, black = dark red
red, blue = magenta
red, green = yellow
red, white = pale red
green, black = dark green
green, blue = cyan
green, yellow = vivid green
green, white = pale green
white, black = grey
white, blue = light blue
white, yellow = pale yellow
white, white = white

In effect, you get 640 resolution for black and white (e.g. text), but
only 320 resolution for dithered colours (with 16 combinations available
in each pair of pixels).

> Every file I try looks horrible.  Also, what do I need to do to use a
> monochrome image?

You can use pure black and white pixels at 640 resolution, plus there
are two dithered 50% greys (which look the same apart from slight
banding effects) at effective 320 resolution.

-- 
David Empson
dempson@actrix.gen.nz