[QuadList] IVC Recovery--"Capture" and "Banding"--

[Ted Langdell]

On May 17, 2014, at 7:17 PM, couryhouse at aol.com wrote:
> I just  bring it into digital and  hit the  save a  still in Sony   Vegas...   or if I am watching analog    footage in  windows media player  I  do a screen capture..... 


I think what Park meant by "capture an image" was "digitize video" not make a still.

His particular process converts composite video to component using the Accom D-Bridge 10-bit decoder before capture as a file... say as 10-bit YUV 4:2:2 in a Quicktime wrapper.

The D-Bridge products (122 and 221) have roots in companies formed by former Ampex engineers:
http://www.abekas.com/main/history//page1059.htm

They were intended to "Bridge" the analog to digital process, including analog composite, D1 parallel and D2 composite.

In a message dated 5/17/2014 4:52:15 P.M. Mountain Standard Time, park at videopark.com writes:
> This is a low band color image from the late 60s, taken with a TK-42.  Notice the lack of banding, hanging dots and cross-color contamination.


The word "banding" can mean two things as related to this post:  

Quad banding... where one sees variations every 16 lines (NTSC) caused by differences in reproduction by each head (EQ, luma, chroma levels for example.)

Or noticeable bands in light to dark areas of the picture caused by the number of bits used in the digitization process. 

You might see this on say a cyc wall where the top is darker than the bottom. Skies are also an example of where banding might easily occur.  

An 8-bit digitization step (255 steps per color) might be more likely to cause a noticeable bands of luma or chroma. 10-bit digitization provides 1023 steps per color, so banding is less likely to occur.

Here's Larry Jordan's take on it with a visual example (originally written in 2007 when ProRes was released):
http://www.larryjordan.biz/why-video-bit-depth-matters/

More bits and a better representation of the original analog signal is one reason why the generally preferred Archival file for SD is 10-bit YUV 4:2:2, and in a Quicktime wrapper, although some archives use AVI if they're PC based.

Ted

Ted Langdell
Secretary
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e-mail:	ted at quadvideotapegroup.com

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