You can't take accurate screenshots from a Voodoo card, as the RAMDAC does additional filtering. There's no way to get the final image, unless you feed it into a VGA capture device.

^ This is true. Hasn't stopped people from trying to reimplment the filter in software though.

All I know is that SUPRGRAB and Hypersnap DX implement the 4x1 filter (the latter has a nag watermark and isn't actually very precise at filtering)

Reproducing the filter effect was once a passion of mine... especially when V2 and V3+ have their own alternative filters.

You can have a look here: 3dfx Voodoo image quality
As I can not edit the posting anymore, all the screenshots can be found here: ftp://retronn.de/pictures/3dfx_compare/
These were taken using a VGA capture card (DVI2PCIe).

Good capture cards go for as low as $20 on ebay at times. Just have a generic search for them, wait around if need be, get one and set it up, and forget software capture (not to say software filter emulation isn't a valid pursuit).

derSammler wrote:

You can't take accurate screenshots from a Voodoo card, as the RAMDAC does additional filtering. There's no way to get the final image, unless you feed it into a VGA capture device.

I see no filtering happening *in* the ICS5342 RAMDAC. If there is digital filtering (upsampling) it happens before RAMDAC, if there is analog filtering, it happens after RAMDAC.

And in fact I just looked at some pictures, and the RAMDAC analog output indeed has "pi" type LC filtering.

Also related to screenshot accuracy but not the filter, there's also the gamma algorithm the V1+V2 cards use that's a bit incorrect and lossy (in whicn Banshee/V3 fixed). You won't be able to capture the gamma bug in screenshots either.

I haven't reproduced 3dfx gamma, but i believe a recursive lookup is involved, with the darker colors being dropped off as the gamma gets higher while overflowing brighter colors back to 0...

@Jepael: Wherever it happens, it happens after the frame has been stored in the frame buffer.

Here is what Suprgrab gives me with the gamma set to 1.0 (The default value, 1.7, is way too bright in Jedi Knight):

You can save it and zoom in yourselves. It almost looks like they added CRT scanlines. In any case, yeah, I'll be staying away from software solutions to get accurate grabs.

but the voodoo1 does add purple lines to the screen which gets even more pronounced with higher gamma settings. It's not just those lines either.

elianda wrote:

You can have a look here: 3dfx Voodoo image quality
As I can not edit the posting anymore, all the screenshots can be found here: ftp://retronn.de/pictures/3dfx_compare/
These were taken using a VGA capture card (DVI2PCIe).

Very cool, thanks. This clearly shows the difference between frame-buffered shot and final image. You were able to force off the dithering filter in environmental variables for your VGA capture; I didn't know you could do such things. If this was to simulate a framebuffer shot, though, why not just use a framebuffer shot? And Voodoos can force a 24bpp mode? Woah. How does this affect framerate?

leileilol wrote:

but the voodoo1 does add purple lines to the screen which gets even more pronounced with higher gamma settings. It's not just those lines either.

Now that you mention it, I can see this effect in elianda's shots. I'm learning a lot from this thread, thanks. *Inserts pensive pipe smoker image*

The "24bpp mode" is a filter toggle and shouldn't affect framerate at all.

The threshold of the filter can also be adjusted so you could make the picture much more blurrier if you'd like. This makes the filter effect even more obivous

Here is a raw, uncompressed capture from a DVI2PCIe Duo. The image needs to be shifted down and to the left; I'm still playing with the settings. If this is accurate, it appears that the default gamma of Suprgrab is more accurate than I gave it credit for.