Super High Res

[thedocbwarren]

Question about this mode (that is 1280x200.)  I've wondered if this mode is for real.  I can't tell since I don't have a monitor yet that works well with my 1200 but when I used the one monitor that seems to display 640x200 fairly well, I figured I'd try 1280x200.  So this mode looks like a ruddy mess and still reports 640x200 on the monitor.  

I read something somwhere about this mode being fast pixels or some such, but other than double-scan I can't imagine what this is.

[thedocbwarren]

I'm bloody confused with all that.  So I have an AGA Amiga (1200) and the mode 'works' just looks blurry.  So I think I userstand the ide behind keeping it 200-256 lines to keep compatibility with broadcast, but I don't understand 1280 if it's not 1280.  So the 'clock' meaning double scan?  It's not  a 30Hz mode so I don't quick get what's doubled if it's not really 1280 pixels across?

What's faster about 16 colours?  I thought it was restricted to 4?

[thedocbwarren]

Yes, it is. Your monitor requires sufficient resolution to use it though.

SuperHires works by doubling the Hires pixel clock to 35 ns. In addition to the normal NTSC and PAL modes it's also used for Productivity, DblPAL, DblNTSC and possibly some other modes with higher horizontal scan rate (and thus lower horizontal and higher vertical resolution).

Not quite following, so it's doubling the 640 res (hense 1280) but I don't get the it's used for other modes.  What's used?

Why does my monitor still report 640x200 but the screen is squished?

Sorry for being thick about this.

[thedocbwarren]

Sounds like you're using a digital monitor - since it's digital it samples the analogue signal and outputs what's been sampled. If the sampling rate is too low (only half of pixel frequency) every other pixel gets lost. As it seems, your monitor has no idea that the Amiga is outputting such a high pixel rate.

Look at the way a video output or (analogue) monitor works: the video hardware just outputs a stream of pixels; for Lores they're 140 ns apart (long), for Hires 70 ns and for SuperHires just 35 ns. In the monitor these pixels modulate an electron beam that scans the screen, moving from left to right. After some time - when the desired line length is reached - a horizontal sync pulse tells the monitor to quit scanning horizontally but move to the next line directly underneath and rewind to the left edge. When the desired frame height is reached a vertical sync pulse tells the monitor to rewind the scanning beam to the top left corner to start the next frame.

A fixed frequency monitor has a constant scan rate to make the beam cover the whole screen during a horizontal or a full vertical sweep. A multisync monitor has to track the vertical and horizontal sync rates and adjusts the sweep rates accordingly.



A digital (flat) monitor is more complex. It samples (A/D converts) the analogue signal into a buffer. To make sure none of the pixels gets lost it's required to pretty exactly match the sampling rate to the pixel rate by using an edge detection algorithm. Note that this exactly the way a flickerfixer works - in theory all flat screen integrate one, but in real life they're usually limited by the extent they can adapt to the signal.

The buffered image (hopefully resembling the original signal) is then output to the display matrix. On LCD screens there's no sweeping beam but rather a continuous memory matrix that you look at, thus the susceptibility to jitter and jerking.

Ok that I get.  So the pixels are crammed in there of which the signal picks up as much as it can for a scan.  This, I assume, is the chroma resolution?

So it seams then the Amiga is packing the signal vs doubling it to get a higher resolution.  I can see how most monitors are unlikely to support this.