Re: IIgs RGB to YPbPr Component experiment

["mdj" <mdj.mdj@gmail.com>]

Michael J. Mahon wrote:

> I believe it was done all the time, particularly in DHR.

I'd say you see this technique more frequently in hires rather than
DHR. DHR colour was seldom used, and since the high order 'shift' bit
is not present in this mode, you're limited to just picking adjoining
'colours' to achieve better looking results.

> The easiest way to check is to look at some of the popular
> paint programs.

I've only familiar with Dazzle Draw, which allowed 140x192
'unrestricted' colour or 560x192 monochrome mixed in the same image.
The only other DHR paint program I'm aware of is 816 Paint, which I've
not played with extensively.

> If you actually visualize the screen as 140 color pixels by 192,
> you get very blocky graphics with bad jaggies.  You can have 4x
> the horizontal resolution on a diagonal line just by casting off
> the shackles of "140 pixels".
>
> The same is true of HGR displays, particularly if they are to be
> viewed in monochrome.  I did it myself in some plotting programs.
>
> The same mindset that considers there to be a fixed 140 pixels
> in DHR might also conclude that there are a fixed 140 pixels in
> HGR as well, neglecting that a white (double) pixel can be plotted
> in any of 279 horizontal positions.

My 'mental model' of HGR is of a 280x192 matrix. colour dots are two
pixel 'wide' but you can cause a byte to be 'shifted' one half dot (in
reality this is two raster dots) changing the colours available in that
byte.

DHR is actually more normalised, as the high order bit is ignored,
meaning all you have are sequences of 4 bits to encode a colour, hence
the usual treatment of it as a 140x192 unrestricted colour mode.

> Apple/Video 7 made design choices that pretty well froze them into
> 140 discrete color pixels across the screen, and that accounts for
> a lot of the discrepancy between the appearance of an RGB display
> and a composite display.

Well, it's hard to come up cohesive models... The only artifacting
trick I'm aware of (ie. have actually played with) is to produce grey
on the hires display.

Matt