Re: IIgs RGB to VGA continued

["Bill Garber" <willy46pa@comcast.net>]

"jsnospam@cimmeri.com" <js@cimmeri.com> wrote in message
1156713219.243460.223020@i42g2000cwa.googlegroups.com">news:1156713219.243460.223020@i42g2000cwa.googlegroups.com...
:
: > In other news, I am also testing a lower cost, prototype unit for
: > RGB->VGA conversion using the Averlogic chipsets.  Results here also
: > look promising so far in all modes up to 320x200.   Still having
: > trouble with 640x200.
:
: Hi, all.   I'd like feedback from those of you who might know what's
: going on here in the following photos.
:
: We've got a prototype VGA converter going using some of the Averlogic
: chips.
:
: All modes except 620x200 are great, but I don't understand yet what's
: going on in 640x200.
:
: First photo:
: http://members.aol.com/mdnttrain/vga1.jpg
: This photo shows GSOS bootup.  What are you seeing here?
:
: I'm seeing two things:
:
:   1) seems like every other vertical line is black.
:
:   2) seems like alternating vertical groups of lines are in color, and
: not.  In the photo only (not when viewing), the groups that are in
: color don't show the in-between blackness as much so you might have a
: hard time seeing.

What I'm seeing is the composite screen, only in color. The composite
output on the IIgs strips color and displays in greyscale (monochrome).

: Second photo:
: http://members.aol.com/mdnttrain/vga2.jpg
: This photo shows the color bands quite well in the GSOS desktop colors
: area.  But note that not every alternate line is black.. sometimes it's
: a colored line.. as in the yellow/pink area.

Wow!  This appears to have something wrong with Horizontal sync.

Pics 3, 4, and 5 have no links.

: Third photo:
: Another desktop view
:
: Fourth photo:
: Booting into Platimum Paint in 320x200 mode, colors are solid and
: perfect.
:
: Fifth photo:
: Same program, switching into 640x200 mode.. reveals all the same
: desktop flaws.  Note again the yellow/pink alternating area is solid..
: suggesting these alternating lines are deliberate and are "dithering."
:
:
: One theory we have for the alternating black lines is that the
: converter and monitor have too much bandwidth to dither.   A SVGA
: monitor shows the dithering that the Apple uses to create colors
: whereas an Apple RGB monitor does not have the bandwidth -- it simply
: shows a solid color because it can't react fast enough to display it
: (done on purpose).
:
: A low pass filter might lower the bandwidth of the SVGA
: monitor/converter combo to equal that of those old monitors.
:
: However, the color banding problem persists.  Would this be some kind
: of color reference signal lock problem?
:
: Thanks in advance for any feedback.
:
: ~ J
: