hvx200 pixel count revealed
 

http://www.dvxuser.com/V6/showthread.php?t=47570

looks like steve mullen nailed it!

Yeah, you gotta hand it to Steve, he figured it out down to the pixel. Well done, Mr. Mullen.

The interesting thing about using pixel shift is that there is no way that the HD video could have 4:2:2 color.

Even Juan said from Andromeda that he never claimed his device gave 4:4:4 in HD modes because the color channels alternate every other pixel. He wasn't sure really what to call it but it is more like a 4:2:? that might actually be closer to a 4:2:0 but without the skipping of the every other line lick in mpeg2 4:2:0. Youwould have true blocks of color that are 2x2 pixels in size but not 2x1 pixels like in a true 4:2:2.

Yes the format records 4:2:2 but the source is not 4:2:2.

Yes it is still slightly better than HDV but not like compaing 4:2:0 to 4:2:2. If the 4:2:2 was the main reason for somebody getting the camera they may have to think about this a little bit more.

With the HVX200 even if you went analog uncompressed the HD is still pixel shifted to give this chroma reduction. With any other HDV camera and analog uncompressed at least you are getting a true 4:2:2.

Thomas, I'm right there with you in that thought.

yeah.. a few people got it.. my favorite was the guys that took it apart and used a microscope to count the pixels. :)

So how is it that the Canon has SDI 4.2.2 color, but employs horizontal pixel shift? Is it because it's only in one axis?

Pixel Shift in the XL H1 is indeed horizontal axis only.

So we enter in a new bad era for video camera , virtual pixel.
now camera can advertise any resolution (or pixel count) regardless to the real one on the CCD.
very sad in fact....

Barlow, not sure I'm exactly answering your question and I'm no tech expert, so those who are may want to amplify/correct, but I'll take a stab at it...

Just as with the Panasonic, the format of the HD-SDI out (4:2:2) has nothing to do with how the signal was obtained within the CCD block or the original detail before processing. It is simply a particular kind of output; the luma and chroma detail within the CCD block get processed, and output in either SDI or HDV, or both. Same with HDV...the 4:2:0 is simply the HDV spec'ed output of the processed signal from the CCD block. So the chroma DETAIL might not quite as sharp as it would be from a true 1920x1080 4:2:2 or 4:4:4 source, but the signal is still 1920x1080 at 4:2:2

yes horizontal is fine for 4:2:2 since you take only every other horizontal chroma sample. You end up with a raw 4:2:2 and then compress to 4:2:0 on the Canon.

Vertical pixel shift on the other hand kills any hope of a true 4:2:2. On the HVX200 the raw image going to the DSP has an odd form of 4:2:0 and then comprsses to 4:2:2.

On a side note however I'm sure the dvcpro50 mode on the HVX200 does give you pretty close to a 4:2:2 since the chroma shifted 1920x1080 is scaled back down to 720x480.

I really do think Panasonic would have been better off going with a 960x720 CCD block. At least then they could claim a true 4:2:2 in 720p mode.

I'm not saying the HVX200 is a bad camera and doesn't have a good image but it is clearly not capable of 4:2:2 like many have hoped.

Regardless of the sample size it appears from tests I did here

http://www.dvinfo.net/conf/showthread.php?t=60877

that the Canon has more colour resolution than the Panasonic even though its 4:2:0 versus 4:2:2, admittedly I was working with jpegs - but still - like for like...

This isn't new at all. I've used a GL1 for the past five years and both it and the XL1 used pixel shift to generate a full 720 x 480 image from 280K pixel CCDs. And both camera's images have looked great.

Not sad at all. This would be bad news only if Pixel Shift was a useless gimmick... but instead Pixel Shift is very real, very useful, and very much a good thing. Pixel Shift is something you want. It's been around for a very long time, and the majority of three-chip video cameras are using it. Pixel Shift provides more sampling points per pixel and actually does increase resolution. What counts is not the actual resolution of the CCD. What counts is the resolution that the DSP provides to the recording mechanism. Remember it was Pixel Shift in both axes that allowed the Canon XL1 to produce very good DV despite having only 250,000 effective pixels per CCD.

I agree Chris but I do think there should be an asterisk next to specs that explain the details. I mean Panny has touted that the CCDs were native 1080p, if not directly, indirectly, same with the 4:2:2 color space.



ash =o)

Or better yet (in my opinion), a paragraph or two in the next generation of HVX200 pre-sales marketing literature entitled "What is Pixel Shift and why is it so important to this camera."

Are you sure that the high-end HD camera use PS? F900? Varicam? Thompson?

Also, I thought the XL1 only used V. PS shift in Frame Mode.

----------------

Clearly you want PS only if the benefits outweigh the negatives. The negatives are that luma resultion is a function of both motion and color content. (It appears that chroma color sampling is also affected negatively -- something I had never considered.)

MOTION: wobulate tha camera and rez. drops significantly.

COLOR: Present it with a red rez. chart on a blue background and resolution drops significantly. Other color combination kill resolution too.

The benefits are twofold:

1) Lower rez. chips are more sensitive so you get a whole stop greater sensitivity with the HVX200. That's important. So VHPS lets these chips yield HD.

2) If the CCDs are already capable of capturing enough resolution to support the recorded format -- then HPS provides OVERSAMPLING.

Although both of these are "benefits" -- they are fundamentally different. In the case of Over-sampling, the worst-case is still equal to the format's resolution. It's like whip-cream on cake.

However, as Adam's test show -- IF the conditions are such as to defeat PS -- the DSP resolution will drop below the recorded format's resolution. Now you lose part of the cake.

But there are two other issues Adam considers.

1) Some manufactures set a camera's anti-aliasing filters low to allow more detail to be recorded. Unfortunately, that allows aliased crap to be recorded too. Unfair? Misleading?

2) Resolution numbers can be boosted by Detail and Edge enhancement. Both Vertical and Horizontal aspects can be enhanced. Unfair? Misleading?

Adam's solution -- which I agree with -- is to not count above where aliasing starts. I also dislike Edge enhancement so I agree with his decision to turn it to down a bit. (Detail is less obviously negative, but can increase noise.)

Clearly Adam will get "worst-case" numbers. And, yes it does favor cameras that use higher pixel counts rather than PS. On the other hand, these high pixel cameras will test much lower on sensitivity.

My solution is to assume that the mid-point between worst-case and best-case reflects real-world performance. But that is an assumption I make only because it's the simplest one to make. Hopefully, it matches what folks see.

btw, thanks for the answers Pete and Thomas.

Steve, you are quite a resource. Whenever I read one of your posts I feel like I've snuck into some kind of video theory symposium.

Thanks for all the technical enlightenment.

Nevertheless, their sensitivity is not so sensitive and the math also multiplies the noise. The pixel count explains alot of why the camera reacts the way it does. Camera in motion is low rez even with OIS on and the noise issues in dark areas of the image are aparent. Still the image colors are very nice. That was a given and I think what really impresses people about Panasonic cameras.

Once again, each camera has it's own user base and anyone willing to work with the camera and learn it will be rewarded with good results.

Hi Steve,

May I ask what is wobulate? Spelling mistake?

TIA

Regards
Leigh

Nice thing about Steve is that not only is he knowledgable, he is also a gentleman.

Hi David,

May I ask why you said that? What is wrong with my question?

Regards
Leigh

Nothing is wrong with your question, Dave was just making an observation.

"wobulate" refers to part of the reference test conducted by Adam Wilt at dv.com, comparing the 4 HD camcorders.

http://dv.com/news/news_item.jhtml;j...leId=177103305

This part of the test correctly checked to see if there was any non-native (chip based) resolution in the camcorders. This resulted in the HVX getting lower resolution marks than what people expected, and led to Steve Mullin come up with his theory of pixel shift on the HVX, whch has been now confirmed from panasonic.

Basically, wobulating (nice word btw) is a test of resolution under camera or subject movement, not stills.

Hi Arjun,

Thanks for the explaination.

Regards
Leigh

Wonulation is also how DLP generate 1080 rows when the DLP chip only has 540 row of mirrors. Each mirror can be deflected one row spacing.

---------

Quote: "Nevertheless, their sensitivity is not so sensitive ...."

Adam found a full stop greater sensitivity. Given that other HD camcorders are typically at least one stop less sensitive than previous SD camcorders -- not good for those of that like to shoot in natural light -- I think 1-stop is important.

Without S/N ratios its hard to judge noise so I can't comment.

insert "cleanly sensitive...." instead.

what about in dvcpro50 mode? is that true 4:2:2?

Thomas from reading your response I would say that you missed some very important information in the article. The signal that comes off of the chip is an analog signal and as such is then captured as a 1080P signal with the 14Bit A/D. It is then with the 19 bit DSP that the signal is manipulated into what ever signal it is that you need. It is a true $;@:2 in HD as it is in SD, DVBCPRO50.

As I suspected all along with the release of numbers, people do not understand. They see a number and that is all they get. Look at the second table and look at the numbers that are effective after pixel shift. You need to appreciate the engineering here as it has its impact, moreso than you seem to give it credit.

Please do not take this as being aimed solely at you as I have bee reading this all over, it is more aimed at all that do not fully understand what that article says. You have to read and understand every part of it as all parts are important. The second stage trsansformation is just as important as the initial chip count and the Spatial Offset. The third part is that DVCPRO HD is a 4:2:2 format, DVCPRO50 is a 4:2:2 format. This camera can intercust with Varicam and the SDX900. You can green screen withit and it does not have the 4:2:0 outline that is on every HDV green screen I have seen.

Hope this helps,

Jan

I've looked at the numbers and description very carefully, and whilst I can fully appreciate how more than 540 lines of resolution can be achieved for luminance, I can not think of any way in which that system could yield more than 540 lines of real vertical resolution for colour, no matter how clever the processing. (As is relevant for green screen work.)

Jan, Thomas and I are obviously not alone in this, so perhaps it would be worthwhile to have an explanation as to how pixel shift technology can improve colour resolution as well as luminance beyond the native chip resolution? To finally lay this matter to rest?

It has already been proven that when the camera is in motion that the real resolution of the chips becomes known. The technology has not eclipsed the camera in motion scenario to retain resolution using pixel shift. There is no substitute for full resolution chips and optics to support that resolution. Panasonic had a price point to hit. I'd say they hit it using some sophisticated means, however, the tradeoff is lower resolution with the camera in motion and noise.

Perhaps I'm over-simplifying this, but can't the color space issue be partially resolved by zooming sufficiently into an HVX uncompressed frame and examing the luma and chroma at the pixel level? I remember with DV you can manipulate the footage until you see the large chroma blocks over the clean Luma portion of the frame. Has anyone tried this with HVX footage?

www.philipwilliams.com

Jan this is exactly why I said it isn't 4:2:0 but somewhere in between 4:2:0 and 4:2:2. Pixel shift works by shifting the green channel to create more luma detail. This does not help the chroma detail in any way except for a slight boost to green tints. There is no way you can suck 960x1080 chroma pixels from 960x540.

Is it much better than 4:2:0? Well of course it is. Any fool can see that we are getting better than 4:2:0.

Even Juan from Reel-Stream has said that using the pixel shift from the DVX100 chips to get HD does not give chroma equal to luma.

In order to have a 4:2:2 and 1080 you would have to have 640x1080 chroma channels. Isn't it true then that through pixel shift the 960x540 luma gets sampled to 1920x1080 and then compressed to 1280x1080? With pixel shift how can all three color channels be doubled the same value when it is a well known fact that pixel shift mainly helps luma?

For keying and 4:2:2 there should be the exact same amount of vertical chroma detail as there is luma detail. If the vertical values differ in any way then it isn't 4:2:2 because 4:2:2 means only a reduction in horizontal chroma detail. Pixel for pixel the vertical value of the luma and chroma are not the same. If no pixel shift was used at all and the 960x540 samples were just upscaled well then yes the luma channels and chroma channels would be exact. Pixel shift however has different weight values on different colors. Maybe if I was shooting a commercial of the Green Giant in front of a green screen (oh god what a nightmare) then yes your chroma channels would also be high in value.

The PS is only relevant for luma and in THEORY generates 1920 by 1080 pixels. Thus, there are 2X more luma than chroma PER ROW and 2X PER COLUMN exactly as required for 4:2:2 sampling.

Every CCD element in the R, G, B CCDs yields one REAL chroma sample. So there should be 960 horizontally and 540 vertically for RBG. In theory there is a luma to chroma ratio of 2X -- exactly what is required for 4:2:2 sampling. And, there are equal numbers of Cr and Cb (960x540) which is the 2:2.

So -- in theory -- the DSP does yield 4:2:2 video.

There are three areas to consider:

First, for DVCPRO 720 there must be 480 and 720 Cr and Cb samples. Clearly there are NOT enough vertical chroma samples. <<< CORRECTION MADE

Second, for DVCPRO 1080 there must be 640 and 1080 Cr and Cb samples. Clearly there are enough chroma samples. <<< CORRECTION MADE

Third, there are not enough luma samples because PS doesn't generate 2X -- it generates about 1.25X more luma samples. <<< CORRECTION MADE

So -- in reality -- the DSP does not have 4:2:2 video. Moreover, there is not enough VERTICAL chroma samples to meet the needs of the DVCPRO codec. <<< CORRECTION MADE

We only need to look at Adam's tests to see that HVX200 luma resolution is much lower than any other 720p camera -- including the old single CCD JVC. And, we can see from the tests that the HVX200 has 1080 resolution that is both neither greater than its "720" resolution and far less than any other 1080 camcorder.

Thankfully these are worst-case numbers, but the design although very clever, can only have real-world performance that is about 20% - 30% better than these numbers. Best-case numbers are only about 35% - 40% better.

Moreover, as far as I can tell, scaling these data to 1280x640 for 1080i does not increase resolution -- although the 1080 codec can carry additional information so it should look clearer.

However, I suspect the best-case numbers come from more edge enhancement dialed in. So you really need to see if you would accept that much enhancement. For going to film -- you really can't have much, if any edge enhancement.

Lastly, there are those who say the image has noise. I can't say! But, calculations can ADD noise and scaling can AMPLIFY noise so I would not be surprised that noise -- especially for 1080 video -- might be higher than some folks would like.

Steve and others,

Question: A raw 4:2:2 format would be able to accurately represent something like a red line followed by a green line followed by a red line and so on, yes? Since the subsampling of the chroma is only in the horizontal direction?

But with the pixel shifting in 1080 mode, there is no way for the HVX200 CCDs to capture red coming and going with each vertical line, nor for it to capture the green coming and going with each vertical line. It would seem that for this case, the CCDs would capture a constant color red field and a constant color green field, resulting in a single constant color image, no? This would seem to be very close to what a native 4:2:0 format would do to the same image, no?

So, am I missing something? Or isn't this fairly close to 4:2:0 for vertical resolution? And for green screen work where the background is truly only a single color, isn't this likely to be closer to the results that could be obtained with 4:2:0?

Please clarify and enlighten, if possible,

Thanks,
Bill

Steve wrote:
"The PS is only relevant for luma and in THEORY generates 1920 by 1080 pixels. Thus, there are 2X more luma than chroma PER ROW and 2X PER COLUMN exactly as required for 4:2:2 sampling.

Every CCD element in the R, G, B CCDs yields one REAL chroma sample. So there should be 960 horizontally and 540 vertically for RBG. In theory there is a luma to chroma ratio of 2X -- exactly what is required for 4:2:2 sampling. And, there are equal numbers of Cr and Cb (960x540) which is the 2:2.

So -- in theory -- the DSP does yield 4:2:2 video."

Confusion: I thought that 4:2:0 has 2x per row and 2x per column, and that 4:2:2 had 2x per column but 1x per row (i.e., full vertical resolution).

And if the theory gives you luma at 1920x1080 but chroma at 960x540, then isn't there 4x more luma, exactly as required by 4:2:0, but half as much as required by 4:2:2?

Bill

I think along the same lines Bill. The extra row is completely interpolated and scaled to 1920x1080. You can't get something from nothing and maybe nearest neighbor or some other interpolation is used.

Great thread -- this is exactly a subject I had wanted someone who knows something to discuss.

Steve Mullen: Agreeing with others here, but it does seem your claim of full chroma for 1080 4:2:2 doesn't jibe with my understanding of the chroma notation (which, by the way, is totally goofball to begin with). I thought 4:2:2 meant "skipped" chroma for each pixel as you move across a row horizontally, but if you traverse a column up or down you have new chroma info at each successive spot. Did you get that wrong perhaps?

One thing I've been thinking about is the "bounding area" for each of the final generated pixels. (By that I mean you trace a line that includes all the area under any R, G or B component that's used in the calculation of any given pixel in the final 1920x1080 grid.) The bounding shapes that result from non-pixel shifted 4:2:0 are quite different than the shapes that HV pixel shifted create. The way they overlap is quite different, and the pattern on the HVX does seem at first glance to be "better" in some quantifiable way, but also seems like it would have some source color patterns that it does well at and other not so well at.

Actually for 4:2:2 and 720p DVCPROHD needs 480x720 chroma samples and for 1080p you need 640x1080. The 480x360 and 640x540 you describe is for 4:2:0 and is exactly what you get with HDV.

You are all correct! I was wrong about 4:2:2. I've made corrections to my post.

All of this means the DSP can NOT yield 4:2:2 and there is inadequate vertical resolution for both 720p and 1080i DVCPRO50 and DVCPRO HD codecs. (Unless, I'm wrong again.)

Unless Jan can explain how Panasonic can in good faith claim PS yields 1920 horizontal pixels (to get the "4" of 4:2:2) and point-out where the missing vertical chroma samples come from -- some real issues have been opened that I never even considered.

"Is the 960x540 pixel matrix, progressively scanned at 60 frames per second, good enough for HD after pixel shift and after Panasonic’s new DSP running their newly coined “Advanced Progressive Technology” APT processing? The short answer is YES INDEED, when compared with the HDV 1/3” CCD camcorders."

http://www.coax.tv/

so now we're saying not even dvcpro50 is 4:2:2? wow, the news gets worse all the time. i thought dvcpro50 was already confirmed at 4:2:2.