6/10/2024

When is 4:2:2 not 4:2:0

4:2:2 is generically interpreted to be 4 samples luma, 2 chroma cr, 2 chroma cb but ignores the field based nature of most video capture

4:2:0 is a somewhat interpretive acknowledgement of the loss between fields interpostively

4:2 is Luma:Chroma over all where ::0 is the alternate state or field where no chroma subsampling takes place and the previous chroma subsampling for the associated field is substituted for the same or similar pixels which are going to take the place of a chroma sample for both fields combined.

 You can think of this as loosing information when the two fields are "smushed" together, or taking advantage of the similar or identical nature of the chroma sample and removing the redundancy.

Some have interpreted this as "skipping" a chroma sample inter field, or only taking a chroma sample every other field on the odd or even field.

This can be true or partially true for MPEG2 in certain cases, unless fields are retained, in which case it returns to 4:2:2 as each field much have its own chroma subsampling field to remain a part of the video stream.. but again this may require a software codec to deal with the extra information.

Whether any hardware codec would expose fields or retain their 4:2:2 format remains to be seen.

DV is "de-interlaced", MPEG2 can be "de-interlaced" or "not de-interlaced"

The DV video format is "progressive" in the sense it is frame and not field based. So a type of de-interlacing does occur as part of the digitization process.

MPEG2 was a more robust standard, in that it was a choice whether to de-interface the fields and then compress or retain the fields and compress. Less motion artifacts could be expected by avoiding de-interlacing. Depending on whether a hardware encoder like a standalone device or software encoder were used might allow this choice or not.

It remains to be seen if DVRs on the low or high end retained fields for capture and playback, varied between brands and models or simply defaulted to de-interlacing.

There are "Profiles" related to bit-rates and features. But I don't think those allowed choosing the de-interlace feature.

MPEG4 and other Professional codec also allowed this choice but its not something people often seek control over.. or understood.

Until we reach a technology can take field based information and infer a depth or object oriented interpretation of the image information and interpolate physics between frames its unlikely de-interlace technology will have improved much. Recent improvements in self driving cars appear to be approaching this level of technology but trickling down to the generic video market will probably take another ten years into the 2030s.

6/07/2024

140/400 is 0.35 still less than 0.5 of 4:2:2, so S-VHS with s-video on MPEG2 is still over kill

Kind of explains why HDV and D-VHS devices standardized on the MPEG2 digitization format with 0.15 overhead before reaching 4:2:2

They were much smaller than DV files or DV storage requirements, and still had far more chroma resolution. For that time.. they were future proof.

Only once the physical line lengths and aspect ratios began to change did they finally have to abandon the MPEG2 720x480x180 formats afforded by 4:2:2 for greater pastures.

80 / 240 is 0.33 just over 25% so DV may be barely enough for Standard Video if using s-video

 I would still be favoring MPEG2 if using s-video with Standard VHS "just in case" and for the convenience of a dedicated capture platform like a DVR, especially one that you could directly off load the video from in MPEG-TS format.. which is more tolerant of dropouts

A full conversion to MPEG-PS for burning DVDs would be likely to introduce more compromises to maintain the stream rate required by those playback formats.

Again, MPEG4 would be preferred to that.. if available.. in a dedicated device, native operating system players will not be encumbered by long expired licensing deals for MPEG2 playback codecs and more likely to be supported by minimally featured playback devices and programs going forwards.

However, MPEG2 capture devices like DVRs are more likely to have dedicated Time Base Correction and Frame Stabilization which is now no longer features included in a purely digital age.

I am biased.. since stumbling on to the ability to offload MPEG2 TS data directly from some of the most premium DVR capture devices ever made.. shortly before they were abandoned and shelved or consigned to the dump.. but their convenience and usage demonstrated by their popularity for about ten years says a lot about their overall effectiveness.

If an MPEG2 capture device like a DVR were used as a pass-thru device to feed an MPEG4 capture device for digitization, that might be the most effective combo and future proof.. but the odds of acquiring and combining them without introducing impedance mismatches or other signal glitches and coordinating them over a long period of time would seem cumbersome.. if only theoretical.


S-Video is not S-VHS, but it can roughly double the Chroma resolution

 

estimate the improvement in chroma resolution for Standard VHS and S-VHS when using s-video.

While S-Video (Y/C) connections can significantly improve video quality compared to composite video connections for both Standard VHS and S-VHS formats, the extent of improvement in chroma resolution specifically can be challenging to quantify precisely. However, we can provide a rough estimate based on typical performance characteristics:

  1. Standard VHS with S-Video:

    • Standard VHS typically offers around 30-40 lines of horizontal chrominance resolution when using composite video connections.
    • With S-Video, the separation of the luminance and chrominance signals reduces color bleeding and improves overall image clarity. It can roughly double the chrominance resolution, providing an estimated improvement of around 60-80 lines of horizontal chrominance resolution.
  2. S-VHS with S-Video:

    • S-VHS offers an improvement in chrominance resolution over Standard VHS, but the exact increase can vary.
    • With S-Video, S-VHS recordings benefit from the same advantages as Standard VHS, but with a higher starting point for chrominance resolution. Therefore, the improvement in chrominance resolution with S-Video for S-VHS may be less dramatic compared to Standard VHS, but it still enhances overall color fidelity and sharpness.

Please note that these estimates are rough approximations and actual performance can vary depending on factors such as tape quality, playback equipment, and recording conditions. Additionally, the perceived improvement in video quality with S-Video connections may also depend on individual preferences and viewing conditions.

DV versus MPEG2 when converting VHS Tapes to Digital

DV uses 4:1:1 chroma subsampling. 

I had an intuitive grasp that DV would be sufficient if not overkill for converting Standard VHS tapes to digital files. I could prove it in numbers, but people continued to preach 4:4:4 was better. - I don't think oversampling the same material that far.. produces any better results and makes handling the converted files that much less likely to be copied or replicated through history.

S-VHS is a superior chroma subsampling on tape, which exceeds that of DV 4:1:1 chroma subsampling, but does not exceed that of MPEG2 4:2:2 subsampling. And direct broadcast signal conversion to digital would be even closer to 4:2:2 which is probably why it was selected for Tivo and other early Broadcast TV digital capture solutions. 4:4:4 was still not warranted however.

A more serious choice is to upgrade to Progressive or retain Field based capture and allow some future algorithm the choice to de-interlace video that has not yet been invented.. possibly even some sort of speculative A.I. de-interlacing method  that minimizes the information loss and artifacts created by early de-interlacing methods. 

Choosing how to archive video tape so that it survives into the future and holds on to as much information as its possible to capture when crossing from analog to digital is a balancing act.

The most important being Luma and Field capture then considering things like chroma sampling or whether to subsample.

In this case using 4:1:1 on Standard VHS (is not) subsampling when converting from Analog to Digital, it is over sampling.

In this case using 4:2:2 on Super VHS (is not) subsampling when converting from Analog to Digital, it is over sampling.

MPEG2 does compress Luma and Chroma for a smaller file size versus DV by a reduction in information in the noise zone of a progressive or field image.. but it is a choice.. and may make handling large video files less of a problem as is the case with DV files.

Given the success of MPEG2 at the time, it was a reasonable tradeoff and quite a success.. judging by the DVD video market of that time.

MPEG4 was introduced as a better version of MPEG2 initially for streaming and low bit rates, but later upgraded in silicon as a higher bit rate replacement for MPEG2 and does not suffer many of the artifacts of an MPEG2 video and is not license encumbered as MPEG2 became. 

Today MPEG4, overall is probably superior to DV or MPEG2 if given a good source to convert. 

However as media degrades, if a DV or MPEG2 conversion is already available, it may make more sense simply to retain that or consider placing it in an MPEG4 container form and format for playback that can conjugate but not re-encode the original digitization process without introducing new artifacts or quality degradation. this when the original source is no longer available, or had degraded further than when the first digitization methods were used.

 


An A.I. perspective on S-VHS versus 4:2:2 sampling

 is S-VHS closer to 4:1:1 or 4:2:2 ?

 

S-VHS (Super VHS) is an improved version of VHS that offers better video quality, especially in terms of resolution and color fidelity. While it's still an analog format, S-VHS does offer enhanced chroma resolution compared to standard VHS.

Here's how it compares to digital chroma subsampling formats like 4:1:1 and 4:2:2:

S-VHS Color Resolution

S-VHS improves upon standard VHS in several ways, including better color resolution. While it still uses a composite video signal,it provides an improvement over VHS in terms of resolution, offering around 400 lines of horizontal resolution for luminance and a slight improvement in chrominance resolution, though specific figures for chrominance resolution in S-VHS can vary. Some estimates suggest an increase to around 60-70 lines of horizontal resolution for chrominance.

Comparison to Digital Chroma Subsampling

When comparing to digital formats:

  • 4:1:1:

    • Luma: 720 pixels per line.
    • Chroma: 180 pixels per line (a quarter of the luma resolution).
  • 4:2:2:

    • Luma: 720 pixels per line.
    • Chroma: 360 pixels per line (half of the luma resolution).

Approximate Digital Equivalent

Given the improved chroma resolution of S-VHS compared to standard VHS, it falls somewhere between 4:1:1 and 4:2:2. Here's why:

  • Chroma Resolution: While S-VHS offers better color resolution than standard VHS, it still falls short of the full 4:2:2 chroma resolution used in digital formats. However, it provides more detail than a mere quarter of the luma resolution, which is characteristic of 4:1:1.

Summary

S-VHS is closer to 4:2:2 in terms of effective color resolution compared to 4:1:1. While it doesn't match the full 4:2:2 resolution, its enhanced chroma resolution surpasses the quarter-luma resolution typically seen in 4:1:1 chroma subsampling. Therefore, S-VHS is closer to 4:2:2 than to 4:1:1, albeit still being an analog format with its own characteristics.