the whole 4:2:2 thing - to David Heath

[BobDiaz]

In reading several of the messages from the last few days, I get the feeling that some people are looking at the numbers and not considering how the image looks.

First, if you are doing any blue or green keying, yes higher color resolution is better. That would give a better edge on your key. However, 4:2:0 keying is still possible.


Assuming that you are not doing any chroma keying, if you look at the videos and stills posted from the HMC-150, the results look really good.

Our eyes are less sensitive to color detail than to black & white detail. This is why color resolution is almost always lower than the luminance (black & white) resolution. So, yes on paper, the 170 does produce higher color resolution than the 150, BUT in a wedding video, business video, or some other video, it's highly unlikely that you or your viewers are going to see the difference.

Both Broadcast TV and Blu-ray transmit the video as 4:2:0. So, the end result won't be able to show the real difference.

The reason for selecting a 170 over the 150 isn't color resolution, but work flow or extra features.


Bob Diaz

 

[trez]

In reading several of the messages from the last few days, I get the feeling that some people are looking at the numbers and not considering how the image looks.
First, if you are doing any blue or green keying, yes higher color resolution is better. That would give a better edge on your key. However, 4:2:0 keying is still possible.

Bob, I'm sorry to say that, but I have the feeling you haven't read those messages carefuly and are missing the point.
Of course 4:2:2 is better than 4:2:0. Nobody says it is not.
What plenty of people say is that HPX170 does not deliver true 4:2:2. Its codec's downsampling factor is 4:2:2 but it carries an upscaled chroma (thus a lot of redundant information).

How will you explain the fact, that HPX170 sensors deliver 960x540 chroma resolution while in the final DVCPRO HD footage (1080) the chroma resolution is 640x1080. Where do these additional 540 vertical chroma samples come from? 960x540 chroma samples is enough to carry all the information the CCDs capture - everything above this is simply an overkill.

The conlusion is that DVCPRO HD codec is not optimal for the HPX170 camera construction. It has been used in this camera because it is a standard - good standard! But this camera is simply not capable of exploiting its full potential (though it is capable of delivering great looking image, of course). This is what this discussion is about.

 

[Bounce]

Bob,

For me, I would rather a camera that does the full 4:2:2 cos I colour grade and composite my footage.

...though I don't do green screen, I do however isolate colours and change them to something else.

Plus a 4:2:2 camera and codec is more colour accurate.




On another point, that XDR capture device would theoretically give you a better image than the 170's DVCPRO codec. Plus 24 bit sound. Plus varying frame rates (I think). Thus a 150 with the XDR may turn out to yield a better image than a 170 on its own - we shall see.

 

[David Jimerson]

Both Broadcast TV and Blu-ray transmit the video as 4:2:0. So, the end result won't be able to show the real difference.

That is true, but there's a big step in between acquisition and the end result where it's pretty important.

 

[Jan_Crittenden]

Bob, I'm sorry to say that, but I have the feeling you haven't read those messages carefuly and are missing the point.
Of course 4:2:2 is better than 4:2:0. Nobody says it is not.
What plenty of people say is that HPX170 does not deliver true 4:2:2. Its codec's downsampling factor is 4:2:2 but it carries an upscaled chroma (thus a lot of redundant information).

The 4:2:2 is from of the DVCPRO Codec, that codec is the same as the codec that is on the Varicam or the HPX2000. It is a 4:2:2 and there is nothing about the chip set that can change this. Those plenty of people that say otherwise, well they are just confused by marketing and not engineering.

How will you explain the fact, that HPX170 sensors deliver 960x540 chroma resolution while in the final DVCPRO HD footage (1080) the chroma resolution is 640x1080. Where do these additional 540 vertical chroma samples come from? 960x540 chroma samples is enough to carry all the information the CCDs capture - everything above this is simply an overkill.

The Sensors on the 170, 150, and the 200/200A are spatially offset to deliver to the DSP an effective 1.1 million pixels by virtue of the spatial offset. That DSP captures the signal at a 1080P capture, all the processing is in the 1080P domain and once the camera processing is over, the Codec comes into play. DVCPRO HD is a 4:2:2 codec which means that there are 2 samples of red and 2 samples of blue for every luminance sample. It also means that there is color on every line.

The conlusion is that DVCPRO HD codec is not optimal for the HPX170 camera construction. It has been used in this camera because it is a standard - good standard! But this camera is simply not capable of exploiting its full potential (though it is capable of delivering great looking image, of course). This is what this discussion is about.

Are there other cameras that have more resolution, yes, but to say that the 170 doesn't exploit the virtures of the DVCPRO HD codec is simply incorrect. Sorry. An I-Frame codec is superior to a Long GOP any day of the week. That is the simple truth.

All the best,

Jan

 

[PerroneFord]

... Those plenty of people that say otherwise, well they are just confused by marketing and not engineering.

An I-Frame codec is superior to a Long GOP any day of the week. That is the simple truth.

What's that you were saying about marketing and not engineering?

I-Frame is superior to Long GOP eh? So my Mini-DV is superior to XDCam? And DVCProHD is superior to HDCamSR?

Right.

 

[Barry_Green]

HDCAM SR is not long-GOP. HDCAM SR is based on MPEG-4, but they use only an intraframe profile. Just like how Sony's own MPEG-IMX is an MPEG-2 implementation but they made it intraframe-only.

I'm certain that Jan was referring to like-for-like, so DV would not be compared to XDCAM (although, of course, you could, since XDCAM uses the exact same DV format/compression as your mini-DV does!) Certainly you meant to say XDCAM-HD or XDCAM-EX, right? But if you want to play "gotcha", you could be "gotcha'd" just like that.

HDCAM SR competes with D5-HD, not with DVCPRO-HD (and yes, they're all I-frame-only). DVCPRO-HD competes against HDCAM, and HDCAM is an I-frame-only codec. Of course, so is every codec Sony ever made for professionals, up until this recent MPEG-2 fascination. DigiBeta, DVCAM, DV, HDCAM, HDCAM-SR, MPEG-IMX, they're all intraframe-only.

 

[BobDiaz]

Correct me if I'm wrong about this, but I'm not aware of any HDTV camera for under $10,000 (USA price) that captures a full 4:2:2 color. Even the Sony EX1 & EX-3 are 4:2:0 color. Both the Canon A1 and H1 are 4:2:0 color.


In the case of the HMC-150, the color is recorded 4:2:0, looking at the color information for each row, first point, it comes together like this (starting at row 100):

Row 100: Color ((Row100+Row101)/2)
Row 101: Color ((Row100+Row101)/2)

Row 102: Color ((Row102+Row103)/2)
Row 103: Color ((Row102+Row103)/2)

...

In the case of the HVX200[a] and the HPX-170, the color is recorded as 4:2:2. Looking in the vertical direction and starting at Row 100, the color would be as follows:

Row 100: Green Pixel Row 100, Red & Blue from (Row 99+Row 101)/2
Row 101: Green from (Row 100+Row102)/2, Red & Blue Row 101
Row 102: Green Pixel Row 102, Red & Blue from (Row 101+Row 103)/2
Row 103: Green from (Row 102+Row104)/2, Red & Blue Row 103
...


The 4:2:2 of the 170 and the 200[a] does provide some color change information for each row, but is NOT as good as a more expensive 2/3" camera that has the full 1080 vertical pixels for RGB.



Bob Diaz

 

[Jan_Crittenden]

What's that you were saying about marketing and not engineering?

I-Frame is superior to Long GOP eh? So my Mini-DV is superior to XDCam? And DVCProHD is superior to HDCamSR?

Right.

Come on Perrone, You know what I meant. And if we were comparing cameras at the same level like DVCPRO 50 and the XDCAM, yeah the DVCPRo50 would be better. Since there isn't an SD $5000 camera or even a $3000 that does XDCAM, it would be hard to say if it would be better. But here we are talking about 1/3" cameras and the diff between long GOP recording codecs and DVCPRO HD, 4:2:0 vs. 4:2:2. and I Frame and 4:2:2 win out.

This isn't marketing, it is engineering.

Best,

Jan

 

[Jan_Crittenden]

Correct me if I'm wrong about this, but I'm not aware of any HDTV camera for under $10,000 (USA price) that captures a full 4:2:2 color. Even the Sony EX1 & EX-3 are 4:2:0 color. Both the Canon A1 and H1 are 4:2:0 color.

Bob, you are wrong.

Best,

Jan

 

[trez]

The 4:2:2 is from of the DVCPRO Codec, that codec is the same as the codec that is on the Varicam or the HPX2000. It is a 4:2:2 and there is nothing about the chip set that can change this. Those plenty of people that say otherwise, well they are just confused by marketing and not engineering.

Jan - everyone here agrees that DVCPRO HD is 4:2:2.

The Sensors on the 170, 150, and the 200/200A are spatially offset to deliver to the DSP an effective 1.1 million pixels by virtue of the spatial offset.

Of course. We all know how pixel-shifting works. It is capable of resolving more LUMA samples than the sensor nominal resolution (1.1 million being an optimistic scenario - it all depends on the image being captured).
However - this has nothing to do with CHROMA!
F.ex. - there's only one sensor capturing red. Its resolution is 960x540. You won' get more samples by combining it with either green or blue sensor output, because they are not sensitive to red at all.
With luma it's very different, because each luma sample is weighted average of three channels - this is why pixel shifting magic works. Each one of the sensors can contribute to luma. Offsetting the green sensor results in the ability to resolve more luma samples.

That DSP captures the signal at a 1080P capture, all the processing is in the 1080P domain and once the camera processing is over, the Codec comes into play.

Of course. This is obvious.

DVCPRO HD is a 4:2:2 codec which means that there are 2 samples of red and 2 samples of blue for every luminance sample.

It's the opposite, actually (2 luminance samples for every chroma sample). Just a typo.

Are there other cameras that have more resolution, yes, but to say that the 170 doesn't exploit the virtures of the DVCPRO HD codec is simply incorrect. Sorry.

Nobody said 170 does not exploit the virtues of the DVCPRO HD codec. I said it did not exploit the full potential of ONE of the codec properties - chroma resolution. Simply because its sensors don't resolve as many chroma samples as the codec can carry. So, some part of the chroma carried by the codec is the result of in-camera math.

Please don't over-interpret my posts. I am Panasonic user and I have good reasons to be one. In my opinion 170 is a better camera than 150! What I attempt to do is to reveal the reasons why it is superior. And 4:2:2 chroma space is not one of them, IMO. I dare to claim you can get the same chroma quality by smoothing the 150 4:2:0 chroma (compression artifacts aside).
Of course I may be wrong. Still waiting for arguments

An I-Frame codec is superior to a Long GOP any day of the week. That is the simple truth.

This is simple truth. To be precise - it all depends on the bitrate and how long the group of picture is... But in the real world implementations the I-Frame codecs are superior to Long GOP ones. So I agree with this one.

Don't get me wrong. I'm not trying to say HPX170 is bad camera. I'm not trying to say that using DVCPRO HD in this camera was wrong decision - it was great!
I'm only trying to say two things:
1. Some of the 170's DVCPRO HD bitrate carries redundant information. Not much, though. Just the tiny fraction of the huge 100Mbit/s bandwidth. Don't get me wrong - the camera exploits the DVCPRO codec as much as it can. It just can exploit it fully due to limited sensor resolution.
2. 170s 4:2:2 chroma is not an advantage over 150's 4:2:0 chroma. When hesitating whether to buy 150 or 170 take other reasons into accounts (and there are MANY)

 

[PerroneFord]

HDCAM SR is not long-GOP. HDCAM SR is based on MPEG-4, but they use only an intraframe profile. Just like how Sony's own MPEG-IMX is an MPEG-2 implementation but they made it intraframe-only.

About 10 minutes after I posted that, I realized that Mpeg4 does have the intraframe mode like AVCIntra. So I have no problem being corrected there.

I'm certain that Jan was referring to like-for-like, so DV would not be compared to XDCAM (although, of course, you could, since XDCAM uses the exact same DV format/compression as your mini-DV does!) Certainly you meant to say XDCAM-HD or XDCAM-EX, right? But if you want to play "gotcha", you could be "gotcha'd" just like that.

Yea, I could be gotcha'd.

HDCAM SR competes with D5-HD, not with DVCPRO-HD (and yes, they're all I-frame-only). DVCPRO-HD competes against HDCAM, and HDCAM is an I-frame-only codec. Of course, so is every codec Sony ever made for professionals, up until this recent MPEG-2 fascination. DigiBeta, DVCAM, DV, HDCAM, HDCAM-SR, MPEG-IMX, they're all intraframe-only.

The thing is, that these threads get so frustrating because of the spin. Probably best if people like myself stay out of them.

I have 2 Panasonic cameras, 2 Canons, and one Sony. They all make me and my clients happy. I'll just leave it at that.

 

[Jan_Crittenden]

Sure - everyone agrees that DVCPRO HD is 4:2:2.
Of course. We all know how pixel-shifting works. It is capable of resolving more LUMA samples than the sensor nominal resolution (1.1 million being an optimistic scenario - it all depends on the image being captured).
However - this has nothing to do with CHROMA!

Actually I am not convinced that everone knows how spatial offset works because thes discussions come up all the time. I have a known 1.1 million pixel imager camera in my lab. I compare it to the HVX200/170. Resolution is virtually the same. Yet everyone looks at the numbers on the chipset and just disses the camera's ability to make competitive pictures or challenge the DVCPRO codec. as you put it. Heck for all you know it may be the lens that is getting in the way of using the entire DVCPRO HD codec. The difference is that the signal coming off of the chips is analog signal, there is not a pixel to pixel relationship to the recording.

F.ex. - there's only one sensor capturing red. Its resolution is 960x540. You won' get more samples by combining it with either green or blue sensor output, because they are not sensitive to red at all.

But there are nuances in other colors say purple that are made up from the red and blue sensor. If there is any tonal gradation, you just added green. There is more resolution to be had. No if the image was only red okay, but how many times is the image only red? Few I would hope, and from my experience that is true, pretty rare for an all red movie. I have looked at spatial offset and it is probably one of the leading technologies out there, it does make something out of what seems to be nothing. We use it in every single camera we make, including the 3000, which is a 2 million pixel imager. Why, because it adds something.

With luma it's very different, because each luma sample is weighted average of three channels - this is why pixel shifting magic works. Each one of the sensors can contribute to luma. Offsetting the green sensor results in the ability to resolve more luma samples.

It is and offset of the red and the blue not the offset of the green. It would make it vastly more difficult as 70% of the image in HD comes from the Green channel.

It's the opposite, actually (2 luminance samples for every chroma sample). Just a typo.

OOps, or 2 chroma red and 2 chroma blue for every 4 green with every line having color.

Please don't over-interpret my posts.

I am only reading your posts as an novice might. And they might be lead down a very different path than the one you are stating now.

I am Panasonic user and I have good reasons to be one. In my opinion 170 is a better camera than 150!

I would agree, but that is because of the DVCPRO HD codec, Intra-frame and 4:2:2.

What I attempt to do is to reveal the reasons why it is superior. And 4:2:2 chroma space is not one of them, IMO. I dare to claim you can get the same chroma quality by smoothing the 150 4:2:0 chroma (compression artifacts aside).
Of course I may be wrong. Still waiting for arguments

Seen it, you can't make 4:2:0 into 4:2:2. Dosen't matter how good the camera is, there is a dead giveaway in the fact that every other line has color.

I'd say it all depends on the bitrate and how long the group of picture is... Of course in the real world implementations most I-Frame codecs are superior to Long GOP ones. So I agree with this one.

I don't think it depends on the bitrate. Seems to be evident in very green screen I have seen for any of the 4:2:0 codecs vs, the 4:2:2 ones.

1. Some of the DVCPRO HD bitrate is used to carry redundant information. Not much, though. Just the tiny fraction of the huge 100Mbit/s bandwidth.

I wouldn't agree with this.

2. 170s 4:2:2 chroma is not an advantage over 150's 4:2:0 chroma. When hesitating whether to buy 150 or 170 take other reasons into accounts (and there are MANY)

[/QUOTE]

If you are doing green screen work, it most definitely is.

All the best,

Jan

 

[kurtmo]

I got decent results keying with a 150. Results. Then again, I'm comparing to the results I got with a DVX100b.

It'd be nice to have someone take some green screen footage with a 150 and a 170 side-by-side and see how they compare.

 

[Jan_Crittenden]

I got decent results keying with a 150. Results. Then again, I'm comparing to the results I got with a DVX100b.

It'd be nice to have someone take some green screen footage with a 150 and a 170 side-by-side and see how they compare.

Exactly. AVCHD is to HD what DV was to SD. If your budget is <$4000 the the results you get with the HMC150 will be better than any other long GOP 4:2:0 codec as the AVCHD codec is a much better codec. When we start talking about the HPX170 and his brother, well we are talking about a camera that costs $2000 more and then there are the P2 cards.

Your result is exactly what I have seen and the differences are in the edges of objects and singular hairs blowing in the wind. Everyone has a budget and if the HMC150 is your budget, you have a fabulous little camera! More money, more better.

All the best,

Jan

 

[Noel Evans]

H
As far as the HPX500 goes, on the up side it's 2/3" chips, and they have proper optical low pass filters to help counter aliasing. (All 1/3" cameras don't, AFAIK). On the other hand, they are 0.5MP chips,

Just popped in to make a small correction. The 500 chips are not 0.5mp. Thats all.

Bit too much number crunching going on here. If you are doing CRITICAL green screen work then I wouldnt use a 150 or a 170. But for most application, both would be fine. The canon A1 does a good job, so stands to reason the 150 would as well .

 

[Bounce]

here in DVX land

Hello.

A correction. The original post was sourced from a google search which gave me an archived forum thread. Because it was about the Panasonic I erroneously claimed it was from dvxuser.com

The original quote was actually from dvinfo.net. See here:

http://www.dvinfo.net/conf/panasoni...sonic-unveils-hmc150-pricing-ship-date-5.html

Also, before anyone starts a debate about the Z1 image quality compared to the 150; it is by now (the original thread is before the release of the 150) clear that the 150 has a significantly better image.


Thanks

 

[trez]

Actually I am not convinced that everone knows how spatial offset works because thes discussions come up all the time.

I read your post and realized I hadn't known it either
You are right - the image is not just plain green or red, but also all the nuances. So, the output of the different subpixel-shifted sensors, sampled at the frequency higher than nominal sensor nominal resolution can resolve that extra chroma information. This is because the photoactive regions overlap (this is true for green/red and green/blue). This actually increases the overall chroma resolution beyond that of single sensor. It's exactly the same process that allows for greater luma resolution.
Thanks for explaining this, Jan! It is simple once you know it, but nobody has been able to clarify this before.

I have looked at spatial offset and it is probably one of the leading technologies out there, it does make something out of what seems to be nothing. We use it in every single camera we make, including the 3000, which is a 2 million pixel imager. Why, because it adds something.

I've always understood how this improves the luma resolution. But it wasn't clear how it affected the chroma. Maybe it's because all the articles about pixel shifting focus on the luminance resolution.
So, because it is the green sensor that is offset biaxially (relative to red/blue), the camera is capable of resolving finer details of, f.ex. the edge between any greenish (greenscreen) area and anything of different color. This will definitely improve greenscreen compositing. Just another reason why greenscreen is more suitable for video than bluescreen! (the pixel-shifting won't work for pure red object on pure blue area).

Now, the important question arises: Does HMC150 HDMI output the real 'pixel-shifting driven' 4:2:2 chroma or is it just the plain 150 4:2:0 chroma upsampled to 4:2:2?

 

[Bounce]

HDCAM SR is not long-GOP. HDCAM SR is based on MPEG-4, but they use only an intraframe profile. Just like how Sony's own MPEG-IMX is an MPEG-2 implementation but they made it intraframe-only.

I'm certain that Jan was referring to like-for-like, so DV would not be compared to XDCAM (although, of course, you could, since XDCAM uses the exact same DV format/compression as your mini-DV does!) Certainly you meant to say XDCAM-HD or XDCAM-EX, right? But if you want to play "gotcha", you could be "gotcha'd" just like that.

HDCAM SR competes with D5-HD, not with DVCPRO-HD (and yes, they're all I-frame-only). DVCPRO-HD competes against HDCAM, and HDCAM is an I-frame-only codec. Of course, so is every codec Sony ever made for professionals, up until this recent MPEG-2 fascination. DigiBeta, DVCAM, DV, HDCAM, HDCAM-SR, MPEG-IMX, they're all intraframe-only.

So, HDV is MPEG-2 and thus long-GOP at 25 megabits.

DVCPRO HD (HVX) is intraframe and 100 megabits.

Would then an MPEG-2 long-GOP at 100 megabits have more info than the DVCPRO HD intraframe?

I ask the more knowledgable - I'm here to learn - please be gentle.

Cheers

 

[ilauzirika]

In the, what matters is how the images look to the eyes of viewers.... about greenscreen....green edges are legit, have you recently seen star wars (the good orginal ones) they are full of green and blue edges.... if those films have edges, edges are the way to go..... I know that they are really old but it doesn't mind...... if you want some greenscreen footage look in the footage subforum.