hvx200 pixel count revealed

[Steve Mullen]

Originally Posted by Chris Hurd

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.

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.

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.

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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.

[Barlow Elton]

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.

[Stephen L. Noe]

Originally Posted by Steve Mullen

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.

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.

[Leigh Wanstead]

Hi Steve,

May I ask what is wobulate? Spelling mistake?

TIA

Regards
Leigh

Originally Posted by Steve Mullen

MOTION: wobulate tha camera and rez. drops significantly.

[David Mintzer]

Originally Posted by Leigh Wanstead

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.

[Leigh Wanstead]

Hi David,

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

Regards
Leigh

Originally Posted by David Mintzer

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

[Arjun Bhuyan]

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.

[Leigh Wanstead]

Hi Arjun,

Thanks for the explaination.

Regards
Leigh

[Steve Mullen]

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.

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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.

[Stephen L. Noe]

Originally Posted by Steve Mullen

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.

insert "cleanly sensitive...." instead.

[Brian Luce]

Originally Posted by Thomas Smet

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


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.

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

[Jan Crittenden Livingston]

Originally Posted by Thomas Smet

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.

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

[David Heath]

Originally Posted by Jan Crittenden Livingston

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.

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?

[Stephen L. Noe]

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.

[Philip Williams]

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