Image quality penalty with DVI => VGA adapter ?

[Malte]

Most card makers seem to only offer DVI with their latest cards. So people like me whose CRT has only VGA / BNC will need a DVI => VGA adapter.

If I buy a new card I would attach such an adapter to the card and continue to use the BNC cable.

Is there a quality penalty when using such an adapter or is the DVI=>VGA conversion neutral to image quality?

[az]

There is no signal conversion involved, it is just a differently shaped plug for analog signals. So instead of a converter you could also just solder the leads of your VGA cable to a DVI plug, if you knew the pinout. There's not much sense in doing that, of course, since those adapters are cheap. I personally wouldn't go with the absolutely cheapest ones, but they should all have next to no effect on image quality. (NOTE: We are of course talking about DVI-A or the analog part of DVI-I here, DVI-D is strictly digital. But this is a non-issue, virtually every DVI output on cards is DVI-I)

AZ

[Ribbit]

The DVI connector has the analog VGA signals on it as well, so the adaptor is just a straight-through connector. So there's no inherent quality loss in the DVI->VGA conversion "process".

In the real world, my guess is it depends on the actual adaptor. I've got an ATi one here, but I've also seen gold-pinned ones selling for stupid prices in my local PC World. I've no idea how much of an issue this [adaptor quality] is though.

[Ribbit]

Damn you Az!!!

[Malte]

Originally posted by az
There is no signal conversion involved, it is just a differently shaped plug for analog signals. So instead of a converter you could also just solder the leads of your VGA cable to a DVI plug, if you knew the pinout.

Okay, that´s what I needed to know, so nothing to worry.

[Fred H]

Some cards have dual outputs, VGA/DVI. I have one, an ASUS Radeon9600XT 128 VIVO. (I still have my Marvel G400-TV in my second PC).
At the present I have an old 19” CRT attached to the VGA output. And, ASUS also attached a DVI->VGA plug I never used.
If my old CRT monitor will “give up” I plan to buy a new TFT monitor with VGA and DVI inputs.
They are a bit more expensive but I assume the DVI quality is much better than the analog.
My first question is: how can you describe the quality improvement of the DVI vs. VGA?
The second question is about DVI and TV. I’ve heard or read somewhere that a TFT monitor with DVI input can simply be used as TV. What they mean? Which HW is needed?
Malte, apologize for using your thread for my dumb questions.

Fred

[az]

There are TV tuner boxes for flat screens, that you just plug into the DVI port. Generally, though, you can get better quality and much more flexibility (and the ability to record to your PC) with a PCI TV card, which is also cheaper.

I can't tell you the rel-world difference of VGA vs. DVI, but in theory, ghosting, blur, washed-out colours, etc, might be visible with VGA, and cannot be visible through DVI. Also, with VGA, you need to synchronize the LCD to the signal frequency, which quite often can only be done very well, but not perfect, resulting in slight flickering. With DVI, none of this is needed.

AZ

[Fred H]

Thanks, az,

Fred

[rylan]

If you can find a DVI-A to BNC cable that would be the way to go so you don't have to have the silly adapter attached to the video port on the card... but I don't know if they're commercially available.
I have some custom designed ones at work for our analog legacy stuff

[az]

You could easily solder yourself one if you had the pinout. Google is your friend

AZ