Question for Adam Wilt (and his response).

[Steve Mullen]

Originally Posted by David Heath

It may be argued that extra chroma res can't do any harm, so 4:2:2 must be better than 4:2:0, mustn't it? I can see the reasoning there, but the bitrate to allow it must come from somewhere, and in 4:2:2 systems where bitrate is constrained that has to mean that the whole image is more highly compressed than if 4:2:0 was used. Hence, is it not conceivable that a better compromise may result from less vertical chroma resolution if it allows lower overall compression, ...?

Finally some sense injected into the non-sense about this topic. The move to progressive means a re-look at the role of horizontal and vertical resolution for both luma and chroma.


Moreover, the claims about the DVCPRO HD codec being better than HDV because ... need to consider the significant differences between 1080i and 720p HDV. They have very few performance areas in common. For example, we read about the need to "paint out artifacts in HDV" yet no mention is made of which HDV.

Didn't we all go through this nonsense when Sony and Panasonic introduced HDCAM and DVCPRO HD?

[Ben Chancey]

I've just got one thing to say. You guys are smart! I am amazed and impressed. Keep up the discussions.

[David Heath]

Originally Posted by Steve Mullen

Finally some sense injected into the non-sense about this topic. The move to progressive means a re-look at the role of horizontal and vertical resolution for both luma and chroma.

A colleague has compared the colour space issue to buying an apartment. Imagine a developer has constructed a block, the overall floor area per apartment is fixed, but that internal space can be divided up any way desired. One estate agent boldly advertises his sales as having a bigger living room, you go and check it out, and his claims are true. But then you realise that it comes at the expense of smaller bedrooms and less storage area. Bringing this up with the agent gets a response of "well sir, you don't want to make too much of the measurements, that's not what's important, it's the overall living experience that counts". Well, yes, he's right, but..... it was the agents who made the biggest fuss about measurements in the first place!

In a way that's all just marketing, and I may do the same if I was selling apartments (or video equipment). In the case of the latter I just find it unfortunate that it can lead to wide technical misconceptions, and I can think of examples where it may be applicable to each of the main manufacturers. I'd rather live in Tokes apartment: "1280x720@10bit@4:2:0" (would need only 25% more with same compression ratio than today's 960x720@8bit@4:2:2) - if I could get the builder to give that extra 25% of floorspace!!

But coming back to the more specifics of colour space, it seems to be much more of an issue within the States than in Europe, and I can't help wondering whether it's because the choice is the States tends to have been 4:1:1 v 4:2:2, whereas in Europe it's been 4:2:0 v 4:2:2. Hence, can it be that what we're seeing is that 4:1:1 is bad v the other two, rather than 4:2:2 is good v the other two? (All else equal, and obviously 4:2:2 should be the best - it's a question of by how much.)

In another thread Barry Green posted some excellent comparisons of the 25, 50, and 100Mbs modes of the HVX. Whilst some obvious comparisons can be drawn between the modes, several factors change between the modes, not just colour space. I asked:

"It's left me thinking that an interesting comparison along the same lines would be to use a Z1 to shoot the same scene as Barry has done, but both in NTSC and PAL SD DV25, all else kept the same. Obviously the vertical resolution will differ, but the big difference between the two examples will be 4:1:1 for NTSC, 4:2:0 for PAL. The compression applied should be the same in each case as both have the same number of samples/second (720*480*30 = 720*576*25 = 10368000 for luminance), so any significant differences in artifacting should be due to colour space, and how the codec handles them.

Any takers?"

If you have a Z1 Steve, I still think that would be a revealing test. It's only with cameras now able to work in more than one mode that these sort of comparisons can be performed.

[Tip McPartland]

Am I wrong or is the term color space being bandied about incorrectly here, as if it is the same thing as chroma resolution? Doesn't color space have more to do with the gamut and bit depth, etc.?

And as for 4:2:0 vs. 4:2:2, the comparison is not always as simple as it looks. For example the 4:2:0 JVC HD100 has significantly more than half the color resolution as the 4:2:2 Varicam.

How so? Because the Varicam downrezzes the 720x1280 spec to 720x960 while the HD100 uses the full horizontal spec.

This means the overall horizontal rez of the HD100 is actually 25% better for both luma and chroma. To put it another way, the JVC has 4 horizontal samples for every 3 the Varicam has. So the more crucial element of resolution, luma, completely favors the JVC over the Varicam.

Now let's get back to chroma, and see if the Varicam really doubles the JVC's chroma resolution. To do that let's calculate total chroma samples in both pictures.

The JVC has 360(V)x640(H)=230,400 chroma samples per frame.

The Varicam has 720(V)x480(H)=345,600 chroma samples per frame.

Turns out that the JVC has 2/3, not half, the chroma rez.

And the JVC also has 25% better luma rez 921,600 samples per frame versus the Varicam's 691,200 -- and we all know that due to the physiology of the eye, that luma resolution is more important.

Of course to put this chroma situation in perspective, people (and networks) have been pleased with SD DV images, say from the DVX100, that only have 86,400 chroma samples per frame, so the JVC's 230,400 may not be so bad since it's, uh, a mere 260% better!

Thanks for flagging the problems in this thread, Steve.

Tip

[Robert Lane]

I'm sorry, but all this over-the-top techno-comparison between formats is very educational (not being sarcastic), but it's also pretty silly do delve into such an academic debate on format choices.

I don't care if it's SD, DV25, DV50, HD, HDV, DVCPRO or even S-VHS.. every format/codec has it's place and a match-to-job requirement that can be fulfilled and used.

You know what really matters? Output. If you want to know firsthand what these format differences really mean or more importantly, what these various cameras actually look like when you shoot them, get to a local pro-video shop, put up the cameras on a test scene with a video switcher and flip between the bodies and look at the outputs.

I'm impressed with the level of technical knowledge being exchanged, but if the point is to really show which is "better" from any single perspective, then the only way you can discern that is to get your eyeballs looking at side-by-side footage comparisons, and not at pages of specs.

And let's not forget one very important aspect of being a "measurbator": You can have the most expensive, technically impressive equipment on the planet but if you don't know how to use it properly and take advantage of what you've got then tech specs become meaningless, don't they?

[Heath McKnight]

Amen, Robert. I choose a camera based on image quality, practicality, and if it's "future-proof" (HDV is future-proof).

heath

[Chris Hurd]

Robert has hit the nail on the head, so to speak, and I can't think of a better conclusion for this thread than his post just above. Thanks to all, but it's time to put this tired topic to sleep.