Archiving video format for capturing VHS?

[JasonCA]

Well, I'm going crazy between trying to understand what's the better of the following formats:

1) 8-bit YUV 4:2:2
2) 8-bit YV12 4:2:2
3) 8-bit RGB 4:4:4
4) 8-bit RGB 4:4:4 Log

For the purposes of archiving VHS, which would be preferable and why?

In terms of YUV, it seems it's not so straightforward to convert YUV to RGB? It seems YUV has a lower data rate then RGB. It also seems to be more lossy over 4:4:4.

RGB seems to have a higher data rate. But it would seem like RGB would be the ideal (loss-less as possible?). Right since it's 4:4:4?

Since most hardware today works in RGB, why not just save it as 4:4:4 RGB even if it requires more data space?

The difference between 4:4:4 and 4:2:2 is that the 4:4:4 seems to provide more robust color information then the 4:2:2 sampling scheme.

And since luminance information has a non linear response to light when captured with a digital CCD, the non linear function tends to requires signal information to be encoded logarithmically.

So, why should I not archive in 8-bit RGB 4:4:4 Log over what seems to be the less quality of 8-bit YUV 4:2:2?

My guess is that YUV better represents the natural way VHS was stored? So, perhaps it's that YUV would be a better archiving format because it more closely resembles that of VHS?

I can't seem to decide! Can someone help me out!

[NJRoadfan]

YUV 4:2:2 is fine. Color on VHS is pretty lousy to begin with, so you won't notice the difference. Just about every consumer level capture card only does 4:2:2 capture anyway. 4:4:4 is reserved for super high end pro equipment.

[JasonCA]

Quote:

Originally Posted by NJRoadfan

YUV 4:2:2 is fine. Color on VHS is pretty lousy to begin with, so you won't notice the difference. Just about every consumer level capture card only does 4:2:2 capture anyway. 4:4:4 is reserved for super high end pro equipment.

Hello NJRoadfan, thanks for the response.

Well, that's what I am trying to understand. Is the 8 bit 4:4:4 RGB really a better format over 8 bit 4:2:2 YUV? I haven't seen 4:4:4 YUV, so I am only comparing between 4:2:2 YUV and 4:4:4 RGB. Regardless of if VHS is not all that great to begin with, which format better preserves the original?

To me, it seems the argument to stay with YUV is because it's most native to VHS. YUV also has a lower bandwidth of data to store. On the other hand, RGB is more common for editors and is lossless, but as a negative seems to consume more bandwidth of data to store.

I think this would be the order:

#1: 8-bit RGB 4:4:4 Log (Best Quality)
#2: 8-bit RGB 4:4:4 (Near Best Quality)
#3: 8-bit YV12 4:2:2 (Really Good)
#4: 8-bit YUV 4:2:2 (Pretty Good)

Seem about right?

[NJRoadfan]

Your capture card only captures YUV format video, any RGB capture option you see is likely doing a color space conversion from YUV 4:2:2 to RGB. Its pointless to use RGB for it. All analog video formats and most digital formats are stored in a luma+chroma format, not RGB. Its a legacy held over from the days of NTSC/PAL/SECAM. Its more efficient to do so as your own eyes don't resolve color as well as they resolve brightness. Even taking that into account, your vision doesn't even resolve red, green, and blue light in a linear fashion. Compression algorithms take this into account. See this page for a great example of such: http://nfggames.com/games/ntsc/visual.shtm

As for why editors use RGB, its easier to do so since thats how computers handle video internally and allows much easier programming. Had backwards compatibility with existing B&W TVs not been a concern, its very likely color video broadcasting might have used an RGB component video signal. CBS was testing a sequential color broadcast standard in thet early 1950s prior to the formation of the NTSC broadcast standard. It used a 72fps video feed and a rotating color disk in front of the TV for 24fps effective color video. DLP TVs use a similar setup to display color today.

http://en.wikipedia.org/wiki/Field-s...l_color_system