Scandoubler schematics

[Zac67]

When fiddling with devices not intended for the Amiga, you'd have to distinguish between scan doublers and flicker fixers.

Simple scan doublers just buffer one 15 kHz line and output it twice at 31 kHz to make it VGA compatible. That's not what you want because you wouldn't get rid if interlace flicker.

Flicker fixers buffer a complete interlaced field and output the previous field in combination with the current one, thus producing a progressive output. OTOH, what you see is partially (the buffered field) already 20 ms older than the rest, which leads to ugly comb/shearing effects.

Wikipedia has a very good article on this.

[Zac67]

Jose wrote:
So how does the 2320 eliminate the comb effect ?

It doesn't. Doesn't even try. Deinterlace interpolation with early 90's technology was out of the question.

[Zac67]

An A2320 / Amber board is probably the best solution you can get; only drawback with the original design is the limitation to 12 bit.

As to deinterlacing effects: for a computer's video output there's no definite solution to the problem. For a video (=camera) type signal there are some interpolation methods that work quite well - but a computer's output is very arbitrary and not predictable. E.g. fonts have to be reproduced very accurately to be easily readable. I doubt if there's a 'perfect' solution to this.

There are two workarounds for this problem:
- limit screen updates to 25/30 Hz - when both fields fit perfectly there will be no artifacts
- use a video card and get rid of this problem alltogether

OTOH what Amiga_3k writes is true: it's no real problem.

[Zac67]

JimS wrote:
It even has a VGA port, although it's only 3 bits/color. One more fpga pin & a resistor per color could fix that.

Then again, that'd make only 12 bit output which is also possible w/ the low budget chips. 24 bit is a bit harder.

Hmm, combining two low cost chips w/ DAC could also be possible: if you use a small resistor array, you could actually 'add' the two analog signals (per color)...