Amiga.org
Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: DamageX on November 11, 2007, 04:59:12 AM
-
http://www.ambery.com/rgbcgatovgac.html
As it is one of the elusive VGA converters that actually supports RGB input on the 15KHz side, the price looks pretty good right?
-
It might be great for an A500, A1000,A2000 or A3000.
But the converter is CGA which means it only has 4096 colors or less. So it is crap for any AGA Amiga. :cry:
-
@DamageX,
Yeah, it does seem like a good price. There are quite a few of these things around, but generally they are around $150+...
@ChaosLord,
Are you sure it will only do 4096 colours? I would expect that since it's analog RGB input, it should be able to handle any colour resolution?
:-?
Cheers,
Mike.
-
Not sure about the 4096 color thing.
On the one hand it does say this:
This RGB converter also helps upgrade 480i component RGB video signals from DVD player or other video devices to progressive scan VGA type for high resolution presentation.
Which if they say you can use it for DVDs that would suggest it does more than 4096 colors or your movies would look like crap.
But, on the other hand they are very specific about calling it a CGA converter over and over again, but I'm pretty sure CGA "provides a fixed set of "16" different colors". As you'll find if you google CGA and number of colors. I tried to hook a CGA monitor up to my Amiga 1000 once and was very disapointed when I found this out.
On the 3rd hand you could just contact them and see and then let us all know. :-)
-
I agree that true CGA is 16 colors and total crap.
The engineers probably said X and the website maker wrote Y.
X and Y are unknown. To solve for X and Y someone must buy one and try it out. :-D
-
Hey, let X = X !!!
-
CGA used a four bit digital 'RGBI' signal, giving 2^4=16 different (ugly) colors.
Actually I can't think imagine this unit is CGA only as it's said to support a variety of consoles - all of which I have never heard of though...
Before you buy it you should ask the dealer whether analogue RGB works.
-
Go at the bottom :
# Input RGB Signals:
* CGA (15K)
* RGB Combined Sync - RGBH+V
* RGB Separate Sync - RGBHV
* RGB Component Video for 480i or 576i
# Input RGB Timings:
* CGA: Horizontal 15KHz Vertical 60Hz
* 480i: Horizontal 15KHz Vertical 60Hz
* 576i: Horizontal 15KHz Vertical 50Hz
So you can use it with AMIGA (you only need how to wire it correctly)
-
FYI...
I asked:
"Hi there,
I'm looking at your product:
http://www.ambery.com/rgbcgatovgac.html
and I have one question for your technical staff: does it support
16bit or 24bit *SAMPLING* color? In other words when it samples the
input signals (RGB/CGA), does it sample at 16bits resolution, or at
24bits resolution?
Thank you very much"
and I got:
"Hi,
Thanks for the email.
The typical CGA RGB or YUV signals are ranged from 4
colors to 16 colors so the sample rate of 8-bit is
applied for most instances.
The max sampling rate of this model is up to 12-bit.
16-bit or 24-bit sampling are used for VGA/SVGA/XGA.
Sincerely,
Support/Ambery.com"
I'm not quite sure how to interpret it: 12bit max, but then can also do 16bit or 24bit? Hopefully it means the latter! :-)
Anyone try it yet?
-
They say CGA but they really mean 15KHz analog RGB.
As for the 16-bit vs 24-bit, I'd have to see what chip was inside. From Ambrey's response I'd say it is a 16-bit Averlogic AL250A with an AL875.
It says "Automatic 50Hz to 60Hz conversion". That is going to make your scrolling suck, but at least it will work on all LCDTV's
-
Dont you just love technical responses from non-technical staff who's first language isnt English!
so the sample rate of 8-bit is applied for most instances
Sample rate, yeah sure ;-)
-
alexh wrote:
Dont you just love technical responses from non-technical staff who's first language isnt English!
Hahahaha, yeah, totally! :-D
Anyways, I'm in agreement with your analysis, although I can't see why they would limit their device to 12bit when the Averlogic chips are plentiful and they do 16bit. I think the answer is simple: they don't have a clue what chips they have in their very own hardware!!
Anyways, so I pressed on and here's an update:
"Hi,
I'm sorry I'm confused, but when you said it does a maximum of 12bit
sampling, then how can it do 16bit or 24bit?
Unless you meant: it can do 12bit sampling on the "CGA inputs", but
will do 16bit or 24bit (which is it?) on the "RGB/VGA inputs". Is that
what you meant?
Thank you"
Note how the question is a trick question as there's only ONE input port on the box!
And I got:
"Hi,
Thanks for the email again.
Yes, that's what we meant. This CGA RGB + YCbCr to VGA
scaler can take either CGA or 480i signals for the
input and it can do 12-bit sampling on the "CGA" RGB
or 480i component RGB.
This unit does not support VGA input and no 16bit or
24bit sampling."
Woa, a totally different response, huh? Confused still?
Make what you will of it, all I know is that I'm glad I'm their only friend ("Thanks for the email again." - must be lonely out there!) :-D
-
I thought about trying this unit, but the lack of specific info along with the 50 -> 60Hz "framerate conversion" (yuk) deterred me. (Plus, I'd wager most scalers around the $100 mark are going to blow, unfortunately.)
-
Perhaps if they had a return policy? I didn't inquire about that.
-
My opinion for the device?
I think it's white. :roll:
-
alexh wrote:
Dont you just love technical responses from non-technical staff who's first language isnt English!
so the sample rate of 8-bit is applied for most instances
Sample rate, yeah sure ;-)
I just figured they worked for Microsoft. The answer, while technically accurate, was not at all helpful
-
@Muzungu:
Hahahaha. Well, the only distinction that would have made them like Microsoft is if they CHARGED for the useless answer :-D Fortunately I conducted the Q&A through email for no cost.
-
Here's my review of the device:
It's small. It uses a small, 5V power adapter. It supports RGB and Component (the sync on green type, I think) video. I cracked it open to check out the chip, but it was hidden behind a glued-on heat sink that I didn't feel like prying off, so that will have to remain a mystery for now. It uses a 16MB SDRAM chip (W9816G6CH-7) for buffering. I was not able to locate useful info regarding another chip: MST9883C-LF
I hooked it up to an A500 and an SGI GDM20E21 monitor, which it synced up to right away. I had to switch the input from Component to RGB since everything looked purple.
After stretching and centering the image, I noticed that the picture seemed rather dull, not as bright as it was on my 1084. This could be because I stretched out an image that was scanning in a smaller area, and the beam had auto-adjusted for intensity based on the screen mode, but not when I tried to spread the same number of electrons over a larger area. I might have to try out one of my LCDs on it later, where electron guns are not an issue. I used SotB as my test game figuring that its touted 50 fps frame rate should give this thing a run for its money. For a few seconds, I sat there and just punched the air to see if there were any signs of screen lag, but detected none. Static objects surrounded by black borders on vertical lines exhibit a slight "shimmering" effect, but things in motion seem fairly smooth. In workbench I detected a slight ghost trail behind the pointer, likely the result of lossy compression. Interlaced WB 1.2 displayed, but it was horrible to look at, like someone had cut the WB into shreds and then overlapped them. Slight color separation is noticeable in hard edges, but I had a combined video cable of about 13 feet, so I'm going to get a VGA gender changer to hook directly to my RGB to VGA adapter from amigakit to see if that improves the picture any. Color separation is not noticeable on complex images, leading me to believe that this device is best designed for JPEG-like images (i.e. photos) as opposed to GIF-like images (i.e. WB screens). At 60Hz, I looked at the screen out of the corner of my eye, where persistence of vision is much less and detected no flicker. This is possibly a function of the monitor itself, but I don't have any response time info for this monitor. I can detect flicker from the corner of my eye in the default screen mode on a 1084.
In summary:
The Good: Fast frame rate, no color loss on OCS games, reasonably sharp picture in complex images
The Bad: No interlace mode support, lossy compression noticeable on WB screens, slight shimmer in VGA mode at black to color boundaries(Although this largely went away in the WXGA mode. I got no sync at all on the SVGA mode.), JPEG-y ghost trail follows moving objects on monochrome backgrounds,color separation on text and similar objects, scrolling text (during the between level segues in SotB) was not as smooth as it could've been, due to separation, ghosting and shimmer.
The Ugly: OK, it actually looks kind of good since it's small and unobtrusive.
Overall, I'm happy with my purchase since it will work just fine for using a 20-inch monitor on my A500 that I plan on turning into an arcade machine for my rec room. I won't be doing any WB stuff with this machine, where most of the problems I encountered turned up.
-
Hi Muzungu,
Thank you for your detailed review.
"Interlaced WB 1.2 displayed, but it was horrible to look at, like someone had cut the WB into shreds and then overlapped them."
Maybe the box doesn't sample or output one of the fields like some tv card software.
John
-
Muzungu wrote:
It uses a 16MB SDRAM chip (W9816G6CH-7) for buffering.
That rules out an Averlogic AL250 as it has the RAM built in.
Muzungu wrote:
MST9883C-LF
A 9883 chip is a triple 8-bit ADC. (It converts analog RGB to Digital).
Muzungu wrote:
I used SotB as my test game figuring that its touted 50 fps frame rate [snip]things in motion seem fairly smooth. [Snip] scrolling text (during the between level segues in SotB) was not as smooth as it could've been, due to separation, ghosting and shimmer.
I would recommend a smooth scroll text in a demo to see the effects of the scandoubler on motion.
Does this scandoubler always output 60Hz? If that is the case, the conversion of 50Hz input to 60Hz output will explain why the scrolling was not smooth.
Muzungu wrote:
In workbench I detected a slight ghost trail behind the pointer, likely the result of lossy compression.
Scandoublers don't compress. If you were in a non-interlaced mode, no idea what it could be.
Muzungu wrote:
Slight color separation is noticeable in hard edges
I think you'll find this is a side effect of the conversion from analog to digital and back to analog.
Muzungu wrote:
At 60Hz
Amiga at 60Hz, or scandoubler at 60Hz?
-
I have an NTSC Amiga, so Amiga at 60Hz and no conversion. I don't know if it will attempt to do a refresh rate conversion, although I have a PAL A1200 I can try it out with this evening.
The ghosting looks exactly like video compression; my guess is that something funky is going on in the DAC, although this device could possibly be using compression in order to maintain performance by sacrificing video quality. HP's RGS-based thin client systems use this to maintain frame rate, so it's not out of the question.
There were a couple of smaller chips in there too that I will attempt to identify.
I re-ran X-out this morning in WXGA mode, and shimmer was no longer noticeable. I'll try WB and SotB again this evening in that mode.
alexh wrote:
I think you'll find this is a side effect of the conversion from analog to digital and back to analog.
Probably. Although I've seen the same effect on VGA when stretched over a 75 foot multi-coax cable. Going from an adapter to a cable to a converter to a cable could be messing with color synchronization.
-
More chip info:
SM8958A SyncMOS micro controller
SPV311A-PL171 DigiShow (This is the chip that had the heat sink stuck to it. It wasn't that hard to remove.)it appears to be an HDTV processor. Interesting too that it appears to be rather obsolete.
-
http://www.superfi.co.uk/index.cfm/page/moreinfo.cfm/Product_ID/1614
does this work
if i change the scart to 23pin amigaRGB
or female scart and use amiga scart rgb cable
-
Muzungu wrote:
The ghosting looks exactly like video compression; my guess is that something funky is going on in the DAC, although this device could possibly be using compression in order to maintain performance by sacrificing video quality.
No scandoubler uses compression. Why would it? The only reason would be to save RAM or bandwidth. Both of which in the case of a scandoubler are MUCH MUCH cheaper than video compression/decompression hardware.
Muzungu wrote:
It uses a 16MB SDRAM chip (W9816G6CH-7) for buffering.
A scandoubler requires approximately 3 lines of 24-bit video, 720*24*3 = 0.42Mbytes. Flicker fixer needs much more 720*576*24*3 = 3.56Mbytes. Both are well below the 16Mbytes in this scandoubler. That chip is 16-bit and has a max effective clock rate of 100MHz = 200Mbyte/sec.
This system has more than enough memory and more than enough bandwidth not to need to compress video.
Muzungu wrote:
HP's RGS-based thin client systems use this to maintain frame rate, so it's not out of the question.
Yes it is out of the question. The system you describe uses a medium which is neither dedicated, nor high bandwidth. A scandoubler doesnt suffer from such constraints. It has it's own dedicated RAM interface which can run at full video speed!
-
After digging more into it, it seems that the ghosting is due to the Comb Filter and 3D Motion Adaptive Deinterlacing and Noise Reduction algorithms the device uses. Since these use interpolation as one means of filling in missing data, it gives rise to the compressed video look that trails a moving pointer across a textureless background. These algorithms are most likely catered to approximate textured backrounds.