DV capture quality sucks

2Bdecided · Member Joined: 21 Nov 2007 Location: United Kingdom

Cedocida does linear interpolation.

vhelp · ..Semi Neutral.. Joined: 31 Mar 2001 Location: New York

As edDV noted earlier, when you work and re-work within DV_4:1:1 you get virtually
no generation loss of original image.

However, once you introduce a color space conversion function -- other than the same codec
used in the original sources processing, assuming that the method is correct -- you risk
generation loss at any level of what is considered original image detail.

A -- What this means is that if you take a color space function and apply a 4:1:1->4:2:0, or
4:1:1->4:2:2, or 4:1:1->4:4:4, you risk some form of generation loss -- aka, rounding errros.
The greater the upsample resolution the less loss. Thus, a 4:1:1->4:2:0 losses more image detail
than a 4:1:1->4:2:2, and so on. Even the averaging of interpolation etc has some rounding errors,
as noted below.

In this analigy above and with the exception to rounding errros, the amount of lost detail is mainily
in the U/V chroma channels (up/down sub-sampled pixels) of the processed image.

The rouding errors spoken of are mainly that of the YUV->RGB, RGB->YUV color space conversions.

B -- most if not all DV_4:1:1 go through an upsampling to 4:2:2, though prob to reduce the amount
of generation loss -- if one were to work inside a 4:1:1 -- and when the aim or final end product
destination is a codec, for instance, in 4:2:0 format as found in MPEG-2 or H264, etc.

A long time ago it was determined that by upsampling to 4:2:2 (or even 4:4:4) you have a greater
resolution of image detail to work with when performing pixel manipulation in image processing, and
when you finally do apply the downsampling to your end product the loss is minimal than if done the
other way.. see below.

C -- don't forget, that during this upsampling/converting, in addition to loosing detail from this function,
that you factor in your final codec destination. Thus, if the end product is MPEG-2 then your DV
(assuming the above analigy) will ultimately go through the following steps to become MPEG-2 video:

BAD ---> 4:1:1->4:2:0->edit/filter->encode[mpeg-2]
GOOD--> 4:1:1->4:2:2->edit/filter->encode[mpeg-2]
BETTER> 4:1:1->4:2:2->encode[mpeg-2]

* in the edit/filter step, there are usually manipulation routines applied to the pixels, be it in a
convolution, median, spacial, temporal or other combinations of these functions.

In the BAD analigy its not saying that it is bad but that it is not as optimum to work in this mode.
In the BETTER analigy it is assume that the video needs no editing/filter and quality loss is not a
factor.

Now, there are many DV codec that employ's decoding routines and as mentioned earlier, that one
of these routines is the upsampling to 4:2:2. And, there have been various errors found in many of
these dv codecs that produce poor results. Some of them were described in jagabo's examples.

Even in the expansive suites of today there are still minor issues realized with the decoding and
color space conversion routines. Adobe is one example, and there is a large year+ long forum
discussion about that problem, and I belive it is still going on to this day. I don't have the URL
to that forum with me. But if I find it, I'll post it up. It was a very interesting read though a
long one at that.

But this vague point I am trying to make here is that to this day there are still problems in dealing
the accuracy of DV codecs and color space processing and that there are no limits to where
or who are the propriators of these products -- the problems still exist, today!

But, for what its worth, I only know of one codec that seems to be the most accurate, and
that is the Cedocida codec. IMO, it is more accurate in its functions than most other dv codecs
out there, today.

-vhelp 4694
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JohnnyMalaria · Member Joined: 29 May 2006 Location: United States

Absolutely right.

I'm still befuddled by the number of high end editing/encoding suites that convert to full RGB before transcoding. What's more, some still get the whole RGB vs. R'G'B' thing wrong.

Our software's internal DV codec performs everything exclusively in the native YCrCb domain at the original sampling level (4:1:1 or 4:2:0). It doesn't even bother to convert the blocks to their spatial locations in the frame.

FWIW, 4:1:1 DV is a bitch to program compared to 4:2:0 due to the "tetris" shaped segments. It adds complexity to algorithms. Getting our letterboxing function to work on 4:1:1 interlaced material in the DCT domain was tedious. 4:2:0 was trivial(ish). All because 720 pixels wide != exact multiple of 32 pixels (the width of a 4:1:1 DV macroblock).

edDV · Posted: May 28, 2008 13:35

JohnnyMalaria · Member Joined: 29 May 2006 Location: United States

edDV · Posted: May 28, 2008 15:07