Found a scan doubler ( who would like one ) ?

[alexh]

IOWASURFER wrote:
http://www.miba51.com/CoCo_VGA_Adpater.html

here is the one Roy worked on for the Atari..

Actually that website shows Roy's first(?) use for his scandoubler, the Tandy Colour Computer (aka CoCo).

I believe its his design or a variation..
The info is on this site..

Yes I think it is, based perhaps on the Averlogic reference design. So far his scandoubler looks to be approx the same design between different computers (Tandy, Atari) perhaps a little evolution between revisions.

AFAIK he tweaks the default register settings to find the best one for each computer. centering, contrast, brightness, overscan etc.

The source code for the "tweaking program" and the I2C emulator is/was available from the Averlogic support site.

I guess you'd have to ask Roy about a cable if you wanted to tweak the settings yourself.

The heart of the scandoubler is/was an Averlogic AL875 ADC and an 16-bit AL250A Scandoubler/Flicker Fixer.

The big downer is that it is 16-bit, which means a fewer colours for AGA screens (which can be 24-bit). The Atari STe and ECS Amiga are 12-bit which are fine.

The little downer is that it probably wont work (well) with every Amiga screen mode possible. But I am sure it will work with PAL/NTSC with and without lace fine.

I hope that this time he uses a sheilded monitor cable instead of a ribbon cable like on the Tandy and Atari.

[alexh]

Not by default.

A quick browse of the internet seems to show the video toaster to have 720 x 480i 60Hz Y/C outputs.

This is an RGB scandoubler by default, but it can be tweaked in software to be a Y/C scandoubler.

You would need to ask Roy about the tweak program and cable.

If anything this would work BETTER with the video toaster than an AGA Amiga because 16-bit Y/C can display more colours than 16-bit RGB.

[alexh]

-D- wrote:
I guess what I'm not understanding is that the link is for a device that connects a coco to an XRGB...

No it aint, it's a CoCo 15KHz RGB to 31khz VGA. I think the URL kinda gives it away ;-)

Granted, if someone can produce a scan doubler + flicker-fixer for $65, I'm sure it would sell very well.

The Averlogic chips are dirt cheap as they are in most low cost LCDTV's.

Roy is making a profit at $65-$75, and so he should, anything less than 50% profit he wont bother making more than a handful.

That said, I dont know how he first sold them (albeit at cost) for $48 including PSU? I guess that was before the decline of the US dollar.

[alexh]

If you intend to use it on an A1000, A500, A600, A2000, A3000 or CDTV (that must be well over 50% of all Amiga's ever made?) then a 16-bit scandoubler wont make an ounce of difference as they are all 12-bit.

Some HDTV's have 16-bit RGB scandoublers.

[alexh]

-D- wrote:
EDIT -- Also, I think it's fair to point out that this unit would be fine for the majority of AGA games/demos (256 color screens). HAM modes aren't used often (at all?) for games at least.

-D- I am sorry man but that is not true! We've had this conversation before. AGA modes (including 256 colour) are 24-bit! For example a 256 colour screen has 256 different, 24-bit colours!

Using a 16-bit scandoubler for AGA demo's and games will give bad results almost all the time.

How bad depends on the colours in the program.

As an example, open this image in windows with a 24-bit (or 32-bit) screen.

http://www.spronkey.com/sdc-gradients.png

Then change the colours to 16-bit. You will see the loss of information on the 256-colour (smooth) gradient bars, but also on the others.

[alexh]

-D- wrote:
Alexh I'm not necessarily disagreeing with that, all I'm saying is that I'm not convinced this unit is 16-bit and/or would b0rk the color output.

And I agree, 24-bit color gradients will look messed up switched to 16-bit. But this isn't exactly the same thing, as AGA isn't capable of *outputting* smooth gradients, since it can't simultaneously display the amount of colors necessary for that (and HAM8 produces nasty color artifacts).

Sorry but you are just thick if you cannot understand it.

The 16-bit scandoubler ignores the 3 LSB's of Red and Blue and 2 LSB's of green. That means that an AGA colour with a blue value of 0 is displayed the same as an AGA colour with a blue value of 7! (assuming the other components are the same)

AGA can display smooth gradients. If say the colours in a program used 256 shades of red for example (highly unlikely but possible) it would have ALL the possible RED shades of a 24-bit screen and if you use a 16-bit scandoubler you would only be able to distinguish 32 of them from the others.

You get a BANDING effect as what was supposed to be a subtle gradient of colours appears as one.

[alexh]

-D- wrote:
Millions of devices around the world use these chips for video playback

Ah, yes but they DONT use the RGB input they use the Y/C input which doesnt need 24-bits for a reasonable colour reproduction

-D- wrote:
It will be at least as capable as any earlier "amiga specific" scandoubler.

Bollox, the Arxon and petsoff scandoublers are both 24-bit RGB scandoublers.

-D- wrote:
Furthermore, if it is indeed using the Averlogic chips which alexh mentioned, they both have 8-bit DACs each for RGB.

Absolutely true. But the AL250a only has 5/6-bit inputs! You cant magically get data back once you've thrown it away!

-D- wrote:
HAM8 mode is essentially a 15-bit *external* output, anyhow.

You've read too much crap off the internet.

[alexh]

quote]
-D- wrote:
LOL, I'm "thick" because because the datasheets for the chips you mentioned state they have 8-bit DACs for each color, yet you keep saying it's 16-bit. That's pretty funny.[/quote]
You know what is funnier... the same datasheet with 5-bit red input, 5-bit blue input and 6-bit green input!

-D- wrote:
Yes, using 256 colors it's possible for a smooth gradient, but as you've stated, highly impractical. Try viewing the image you linked to on an AGA screen, and it will look like ass.

Look at the RED bit in one AGA screen, BLUE bit in another and GREEN in another and they look IDENTICAL to the PC in AGA!

-D- wrote:
Due to the very nature of how HAM works, you get fugly looking images, gradients included. This even has nothing to do with HAM8 not being a 24-bit output in the sense of displayable colors, regardless of the internal palette.

No HAM8, just regular AGA screen mode, any number of colours you like. 256, 32, 8.

Choose a different 24-bit palette entry value for each colour where only the LSB's are different.

With an AGA paint package, paint the background in one of these colours and write your name using the different colours.

Look at it on your XRGB monitor... yep cool... "-D-"

Now use a 16-bit scandoubler... but wait... I cant see anything... everything looks the same colour!!

ARRRGHHH!!!

[alexh]

One other thing I should point out is that the scandoubler is not (by default) a frequency shifter, and so PAL screens are still 50Hz and may not display on some LCD panels.

[alexh]

-D- wrote:
BUT, I can't find anything in the datasheet for the AL250a indicating a castrated input, however, I'm open to correction.

http://www.averlogic.com/admin_en/product_en/pic8/540738.pdf

Look at the number of bits on the input on the diagram on page 1. 16-bits

-D- wrote:
if I have to eat shoe, I will :-p

Nowt bad about being wrong mate, happens to me several times a day, you just pick yourself up, learn from it and get on with it. Makes you a stonger engineer.

[alexh]

-D- wrote:
Get over yourself. 256 color gradients, yes.

No, no, no.

Not just 256 colour gradients. (Although these are the most obvious)

Any AGA screen.

If the colours use the lower 3-bits of each colour component, and there are several of them separated by only these bits. They will appear as one colour.

It is particularly noticable on AGA 3D demo's with light shading, AGA monochrome demo effects, AGA 2D pictures with flesh tones or halo's (like say from a candle).

[alexh]

Darrin wrote:
I'd be more interested in someone using one to run Zool2 AGA, Gunship 2000 AGA or UFO Enemy Unknown AGA and letting us know if they are "aware" of any problems when playing a game.

Probably not. You'd just shrug off having fewer colours as being part of the game. DCE FlickerMagic/ScanMagic internal scandoublers are I think 16-bit and they are widely used. I think only recently did it come to light that they were (but I am probably wrong and when they came out everyone hated them, but then forgot the limitation over time ;-))

I would imagine that using WinUAE with the aforementioned games and switching to a 16-bit direct colour mode may have the same effect as a 16-bit scandoubler. Try it.

[alexh]

nBit7 wrote:
To be able to reproduce the full 16M colours would require using more than 24bits (3*8bits) at the analogue to digital converter (ADC).

Not that it matters, but internal scandoublers, like the Arxon and Petsoff and DCE FlickerMagic / ScanMagic etc. dont have ADC's. They get their RGB information in digital form direct from the chips (Lisa/Denise).

For the best picture quality and colour representation the AL250a could be used on it's own directly attached to the Lisa/Denise chips without an AL875 ADC, but it would be and "Amiga only" solution. You'd need a different one for ECS and AGA Amiga's. It wouldnt be worth it. And it would still be 16-bit ;-)

[alexh]

hardlink wrote:
So for 16-bit quality, you think the AL250a would work? Does it need external RAM?

Yes, no.

[alexh]

adonay wrote:
would a CM-345S scan with 24 bit?

I would think so, but it would be best to test empirically. They use the SmartASIC STV108 Scandoubler which can do 24-bit input.

http://www.amiga.org/gallery/index.php?n=1176=38