Color resolution when downconverting to SD at DVinfo.net

Go Back   DV Info Net > High Definition Video Acquisition > General HD (720 / 1080) Acquisition

General HD (720 / 1080) Acquisition
Topics about HD production.


Reply
 
Thread Tools Search this Thread
Old January 31st, 2006, 12:11 PM   #1
Regular Crew
 
Join Date: Sep 2005
Location: Norway
Posts: 123
Color resolution when downconverting to SD

I have read several places that HDV color resolution, when downconverted to SD in the right codec, can hold 4:2:2 colors.

Can anyone verify this, and if so explain exactly how it works ?
Kristian Indrehus is offline   Reply With Quote
Old January 31st, 2006, 01:45 PM   #2
Regular Crew
 
Join Date: Jan 2005
Location: Belgium
Posts: 139
1080i HDV (1440x1080 pixels, 4:2:0) contains 720x540 chroma values (Cr and Cb). Enough for 4:4:4 SD (NTSC). Your NLE shouldn't lose chroma values when downsizing. It will in all likeliness decompress the HDV material to uncompressed 4:4:4 or 4:2:2 before the downscale to SD.
__________________
Please keep in mind that English is not my native language.
Ben De Rydt is offline   Reply With Quote
Old January 31st, 2006, 02:53 PM   #3
Trustee
 
Join Date: Feb 2004
Location: Brookline, MA
Posts: 1,447
Now that's a great reason to shoot in HD.
Emre Safak is offline   Reply With Quote
Old January 31st, 2006, 03:01 PM   #4
Trustee
 
Join Date: Aug 2003
Location: Vancouver BC Canada
Posts: 1,315
When you are downsampling resolution, as long as it is into a codec that will not restrict colour(chroma) info, the downsample will not stay locked at the origional 4:2:0, but will condense the chroma info that it has available. If that is SD 4:4:4, it will take advantage of that space. You aren't gaining anything, you are just condensing what was already there.

For best results I have found using a codec that does intelligent upsampling to 4:2:2, such as AspectHD. Then perform FX work or do CC in 16bit rendered out uncompressed or other non-restrictive codec. When all is done downsample to SD uncompressed and then render to DVD. I see the point of having the prestine 4:4:4 SD downsample, is it allows super quality DVD's. Very pro looking. I see the pre-downsampled HD as the best to do FX manipulation on, as the final downsample "cleans" everything up. Thats my preferance.
__________________
Damnit Jim, I'm a film maker not a sysytems tech.
Ken Hodson is offline   Reply With Quote
Old January 31st, 2006, 03:17 PM   #5
Major Player
 
Join Date: Nov 2004
Location: Canada
Posts: 547
Agreed with Ken on all accounts.

-Steve
Steven White is offline   Reply With Quote
Old January 31st, 2006, 03:49 PM   #6
Major Player
 
Join Date: Sep 2003
Location: Solana Beach, CA
Posts: 853
Well said Ken.... When SD is the final intended output, the "oversampling" afforded by the source HD signal produces very professional looking SD by increasing the effective chroma fidelity of the SD output compared to the 4:2:0 HD source.
David Taylor is offline   Reply With Quote
Old February 1st, 2006, 12:50 PM   #7
Regular Crew
 
Join Date: Sep 2005
Location: Norway
Posts: 123
Quote:
Originally Posted by Emre Safak
Now that's a great reason to shoot in HD.
My point exactly :)

Thanks guys for the valuable information. Now the follow-up question:

Will the condensed color (now 4:2:2 or 4:4:4) be an advantage (compared to SD 4:2:0) when pulling keys and doing blue-screen work?
Kristian Indrehus is offline   Reply With Quote
Old February 1st, 2006, 02:06 PM   #8
Major Player
 
Join Date: Sep 2003
Location: Solana Beach, CA
Posts: 853
Quote:
Originally Posted by Per Kristian Indrehus
My point exactly :)

Will the condensed color (now 4:2:2 or 4:4:4) be an advantage (compared to SD 4:2:0) when pulling keys and doing blue-screen work?
You bet.... But SD is not usually 4:2:0 unless it's been converted into or captured (less common) in MPEG. Most forms of DV are 4:1:1, but the answer of "you bet" still applies for 4:1:1 DV source.
David Taylor is offline   Reply With Quote
Old February 1st, 2006, 05:39 PM   #9
Inner Circle
 
Join Date: Jan 2006
Posts: 2,699
Quote:
Originally Posted by David Taylor
But SD is not usually 4:2:0 unless it's been converted into or captured (less common) in MPEG. Most forms of DV are 4:1:1,........
That's true in 60Hz countries, but the previous poster is from Norway. For PAL, SD normally is 4:2:0 in the DV variants, at least as far as DV and DVCAM are concerned, the exception here being DVCPRO which is 4:1:1. (And that is far less common than the other two.) An obvious advantage is when a DVD is the end product - using DV or DVCAM means the same colour space (4:2:0)exists throughout the production process.
David Heath is offline   Reply With Quote
Old February 3rd, 2006, 09:33 AM   #10
Major Player
 
Join Date: Mar 2005
Location: Northampton, England
Posts: 500
Quote:
Originally Posted by David Heath
An obvious advantage is when a DVD is the end product - using DV or DVCAM means the same colour space (4:2:0)exists throughout the production process.
Almost... except the 4:2:0 sampling on a DVD is different in structure to the 4:2:0 sampling used in PAL DV...
__________________
Alex
Alex Leith is offline   Reply With Quote
Old February 3rd, 2006, 05:47 PM   #11
Inner Circle
 
Join Date: Jan 2006
Posts: 2,699
Quote:
Originally Posted by Alex Leith
........the 4:2:0 sampling on a DVD is different in structure to the 4:2:0 sampling used in PAL DV...
Could you elaborate? I'm aware that a DVD uses MPEG2, whereas DV is intra frame compression only, but my quote referred to colour space which I thought was the same in each case. Or am I missing something?
David Heath is offline   Reply With Quote
Old February 4th, 2006, 02:57 AM   #12
Major Player
 
Join Date: Mar 2005
Location: Northampton, England
Posts: 500
Quote:
Originally Posted by David Heath
Could you elaborate? I'm aware that a DVD uses MPEG2, whereas DV is intra frame compression only, but my quote referred to colour space which I thought was the same in each case. Or am I missing something?
Basically the matrix of colour samples are a different shape.

PAL DV uses co-sited 4:2:0. Cb and Cr are sampled with every second Luminance samples on alternating lines. It goes:

Line A: Y+Cb, Y, Y+Cb, Y
Line B: Y+Cr, Y, Y+Cr, Y

MPEG-2 uses inter-sited 4:2:0. Cb and Cr are still sampled on alternating lines, but they're offset from the Luminance samples (which is a little hard to depict without a graphic). It (sort of) goes:

Line A: Y, Cb, Y, Cb
Line B: Y, Cr, Y, Cr.

So basically the colour samples for MPEG don't directly align with the colour samples for DV (either PAL or NTSC).
__________________
Alex
Alex Leith is offline   Reply
Reply

DV Info Net refers all where-to-buy and where-to-rent questions exclusively to these trusted full line dealers and rental houses...

Professional Video
(800) 833-4801
Portland, OR

B&H Photo Video
(866) 521-7381
New York, NY

Z.G.C.
(973) 335-4460
Mountain Lakes, NJ

Abel Cine Tech
(888) 700-4416
N.Y. NY & L.A. CA

Precision Camera
(800) 677-1023
Austin, TX

DV Info Net also encourages you to support local businesses and buy from an authorized dealer in your neighborhood.
  You are here: DV Info Net > High Definition Video Acquisition > General HD (720 / 1080) Acquisition

Thread Tools Search this Thread
Search this Thread:

Advanced Search

 



Google
 

All times are GMT -6. The time now is 12:27 AM.


DV Info Net -- Real Names, Real People, Real Info!
1998-2017 The Digital Video Information Network