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Re: 15Hz to VGA converter



On 8/13/2010 7:02 PM, MdntTrain wrote:
On Aug 13, 4:06 pm, Steven Hirsch<snhir...@gmail.com>  wrote:

The Highway Model 100 converter does a FAR better job on the desktop.

Yes.   Reposting some of my old photos, you can see the differences:

http://www.cimmeri.com/js/download/

RGB1-7.JPG = IIGS ->  Keene Aptus ->  Samsung 192MP
                     = RGB ->  RGB/YUV ->  15khz YPbPr in
                     = A-A-(A-D upsampled to LCD)

     Problems seen on desktop are due to the 192's high bandwidth
      Component input, and its sampling rate creating aliasing effects.

     The Samsung 910MP with SCART does NOT have this problem
     as the SCART input is bandwidth limited.

rgbvga1-6.jpg = IIGS ->  Highway100 ->  Sony Trinitron CRT
                     = RGB ->  RGB/VGA ->  31khz VGA in
                     = A-(A-D resampled D-A)-A

      In this case, the Highway's SCART RGB input is either
sufficiently
  bandwidth limited to prevent the desktop problems, OR, its sample
rate
is such that the aliasings do not occur (the internal tech specs are
unknown).



It looks like the Highway 100 VGA properly supports "240p" video (the XRGB2+ does as well). Most of the cheapo upscan converters treat all video sources as 480i. The result is that you get the scan line effect since one field has video, and the other field is blank.

   Note that a major advantage of the Highway 100 /VGA is that you're
now at "progressive scan" or 400 lines rather than 200... no
interlacing.
Compare this with the svid photos which are a normal interlaced CRT.

Also, a different problem occurs in svid10.jpg.   Is this aliasing?
This
is a pure analog chain, so nope.  Rather, I believe these bars result
from
insufficient NTSC colorburst bandwidth.

- jS

You get scan lines because of the interlacing, which leads to my next observation. When directly connected to a better 15.75khz RGB CRT monitor (Toshiba TIMM, NEC Multisync II, etc.), you can clearly see scan lines in the output from the IIgs!