drkenb wrote:
On Aug 13, 4:18 am, Michael J. Mahon <mjma...@aol.com> wrote:Mark Frischknecht <appleii...@gmail.com> wrote:Thanks to a tip James Littlejohn gave me I purchased a 15Khz RGB CGA YUV Component Video YCbCr to VGA Converter Scaler from http://www.ambery.com/rgbcgatovgac.htmlWiring up the cabe was quite easy:IIGS VGA 15 pin Pin 1 Gnd --------> Pin 5 Gnd Pin 2 Red --------> Pin 1 Red Pin 3 CSYNC ---> Pin 13 HSYNC / CSYNC Pin 5 Grn ---------> Pin 2 Grn Pin 9 Blu ---------> Pin 3 BluI posted pictures of the video output on my Picasa albums: http://picasaweb.google.com/AppleIIguy/CGAComponentToVGA#It looks like 640x400 dithered doesn't come out to well...It would be good to see the GSOS desktop. That seems to be an "acid test" of a converter's response to 16MHz dither--and a good indication of what a user will see all the time.Hi Michael - He does have one screenshot of the Finder desktop. And you're correct - that is the acid test for these devices!
When I "paged" through them yesterday, I didn't see the desktop. Yep--pretty ugly. There are only two choices for good conversion: 1) phase lock to the *actual* dot clock of the source, or 2) oversample by a significant factor (I'd say 3x or better) to avoid aliasing. So far, no affordable converter seems to do either of these things. After resampling to VGA standards, if the video is presented to a digital display (LCD), then the LCD's logic is responsible for further resampling to its own dot pitch--which a good display should do without further artifacts, assuming that the display's resolution exceeds the resolution of the IIgs video (which for a VGA display is certain). It is perfectly fine to display the fine lines of the dithering without any need to "blur" them into a uniform background. A fine "crosshatch" is also visually pleasing. A coarse aliased "beat" between the alternating fine vertical lines and the sampling clock is *not* pleasing. To sum up: the problem is *not* excessive display resolution. The problem is visible "beats" between the IIgs dot clock and the sampling clock. One way to prevent the beats would be to limit the bandwidth of IIgs video signals to about 8-10MHz, but that would blur all the features of the display, too. I suspect most IIgs users would not like the compromise, but it might be worth a try... -michael NadaNet and AppleCrate II: parallel computing for Apple II computers! Home page: http://home.comcast.net/~mjmahon "The wastebasket is our most important design tool--and it's seriously underused."