.......if there is too much change between frames (such as often happens in nature or if flash photography is involved) the first frame may get overloaded with information, and will leave about 10% of the data rate for the rest of the frames in the group.
This shouldn't be the case, and isn't with any good long-GOP codec.

The allocation of bitrate to ref frames and difference frames is dynamic, so the situation you describe shouldn't happen. On a static scene the diff frames don't get allocated much data (they don't need it), but with a lot of movement the ref frames get allocated less, the difference frames more.

Imagine two extreme cases, one with NO movement, the other basically a succession of random images frame by frame. If 25fps, 50 Mbs, and a GOP of 12, you could allocate the bitrate in two (extreme) ways

1. Allocate 25Mbs to each I frame, (two every second), and none to the difference frames.
2. Allocate 2Mbs to EVERY frame - difference frames getting the same as I frames.

1 would (theoretically) be optimum for a completely static scene, 2 would be optimum for the succession of unrelated images. In practice, real life situations fall between these two stools, but the underlying principle holds good. Less movement =less bits to diff frames. More movement =more bits to diff frames (and less to I frames)

It follows that for the same bitrate, and all else equal, a long-GOP system MUST be better in terms of quality than an I-frame only one. The debate starts when bitrates aren't equal - at what ratio can the qualities be said to be "equivalent"? The generally held figure is about 2-3x - that's why the equivalence between XDCAM422 and AVC-Intra 100 shouldn't come as any surprise - in spite of the 2:1 bitrate difference.

To me, it is highly questionable as to whether or not the HPX250 is an improvement over the HPX170. Panasonic could have chosen to dominate the ENG camcorder field by upgrading the three-CCD imaging block and the global shutter of the 170 to a true 1080p array, but chose instead to substitute its already-developed MOS-rolling shutter imaging block for the 250. Very disappointing, although good for those on a limited budget who aren't doing fast action video. Neither the new Canon C300 nor the Scarlet have incorporated CCDs or global shutters. Panasonic has missed a great opportunity here. Maybe they should consider an HPX350 at up to an $ 8500 price point with the aformentioned quality imaging block. Until then, I'll stay with my HPX170 until side-by-side tests demonstrate a rolling shutter without significant problems in fast-action shots.

To me, it is highly questionable as to whether or not the HPX250 is an improvement over the HPX170. Panasonic could have chosen to dominate the ENG camcorder field by upgrading the three-CCD imaging block and the global shutter of the 170 to a true 1080p array, but chose instead ...............
It's a nice wish, but think about it. What you want involves shrinking the size of the 170s pixels by a factor of well over 4 (well over, because of the guard spacing), if they'd stayed with CCD, what do you think the noise, sensitivity etc would be like? (The 170 is not exactly the most noise free camera in the first place.)

Basically, the choice was go to CMOS, develop bigger than 1/3" chips, or stay with 960x540.

As more and more displays become "full HD" (1920x1080) the differences between the 170 and cameras like the EX were becoming more and more noticeable - have you seen the two intercut? Hence the last option (stay at 960x540) gets ruled out. You'd need 2/3" to keep the pixel size the same and go to 1920x1080 - which becomes hardly practicable in this size and price of camera.

Hence CMOS.

So David, if I understand correctly, the increased sensor size necessary for a full-frame 1080 3-CCD camera would be too large for an HPX 170 sized or slightly larger camcorder, because the CCD sensor subunits are considerably larger than the CMOS subunits ? Or is it that with the rolling shutter, the CMOS chip doesn't need a full set of sensor subunits - instead, the same subunits are re-scanned slightly later with a different portion of the frame ? Sorry for the basic questions, but my knowledge of the detailed workings of an image block is rather limited.

Just one more slightly off-topic question, David. Several manufacturers are now making CMOS sensors with global shutters. Do you see this as the next major advance in the field of prosumer and professional video cameras ?

Mark - the fundamental issue is that matters like sensitivity and highlight handling etc are heavily dependent on the size of individual photosites. Pack more onto a chip of the same size, and inevitably they become smaller - hence a compromise between resolution and sensitivity.

The only way to improve one without compromising the other is to move to a larger sensor or change the technology. The HVX171 is not the most sensitive of cameras as it stands - going to 1920x1080 and keeping 1/3" CCDs wasn't an option. Hence - bigger chips, or CMOS.

Bigger chips (you'd need 2/3" to keep the photosite size the same as the 171, whilst moving up to 1920x1080) mean bigger, heavier, more expensive lenses. Not really practical in a camera of the form factor/cost we're talking about here. Hence CMOS.

I'm not aware of any cameras currently that have CMOS/global shutter - do you have any references? Is it "the next major advance"? Probably depends what you do - some people get very disturbed by the effect, other people find it less of an issue. Even if not a global shutter, differing cameras have different readout times - mobile phone etc video shows it far worse than a true camcorder, even if both CMOS.

It will be interesting to see what the new Canon C300 is like in this respect. It uses a simplified readout compared to standard deBayering, which may make it relatively fast and hence may mean lessened rolling shutter effects. (Their readout method - see the C300 thread - is not new, what is new is that it's being applied to a sensor with the optimum pixel count for the technique, twice 1920 horizontally, twice 1080 vertically.)

Several manufacturers are now making CMOS sensors with global shutters.

Who is making global shutter cmos Mark?

Two companies came up quickly on a Google search, and I believe that there are others as well. The first one, Teledyne DALSA is producing Falcon high-speed cameras with CMOS chips and global shutters (www.teledynedalsa.com), and the second one appears to be a chip distributor named Viimagic (CMOS image sensor, Imaging sensor (http://www.viimagic.com)). They are advertising a HDTV sensor chip that is CMOS with a global shutter, Apparently Kodak labs wrote some papers on CMOS with global shutters back in 2003, but the technology has been slow to come to market.

The Panny looks like a great buy for those who've already taken the plunge with P2 cards. Not so good if you don't have them. Having said that, the card prices are not as bad as they were, and there seems to be a decent resale value in them.

It'll be interesting to see the camera side by side with the canon, but there is another excellent budget option. The mighty EX1 pops up on Ebay (often with very few hours on the clock) at half price with batteries, SxS card etc. The budget conscious can get a lot of camera for their cash, and even sell the camera on at little loss should they wish to move on to something else.

Two companies came up quickly on a Google search, and I believe that there are others as well. The first one, Teledyne DALSA is producing Falcon high-speed cameras with CMOS chips and global shutters (Teledyne DALSA (http://www.teledynedalsa.com)), and the second one appears to be a chip distributor named Viimagic (CMOS image sensor, Imaging sensor (http://www.viimagic.com)). They are advertising a HDTV sensor chip that is CMOS with a global shutter, Apparently Kodak labs wrote some papers on CMOS with global shutters back in 2003, but the technology has been slow to come to market.

Interesting... Looks like camera making companies will have to make their own sensors - they wont buy it from other companies...

The Panny looks like a great buy for those who've already taken the plunge with P2 cards. Not so good if you don't have them. Having said that, the card prices are not as bad as they were, and there seems to be a decent resale value in them.

That's what I am thinking to. People who are already heavily invested in P2 will definitely be looking at another P2 camera. But it looks like that this is the only reason why somebody would buy another P2 camera from Panasonic. Because as of now they don't have a P2 camera that followed the trends of the market. Excluding the varicam ENG series of cameras.

This troubles me to. I'm also invested in P2 but don't really want to buy the next camera from Panasonic. Give me an AF100 with P2 and you got me sold! Or a reasonably priced 2/3 ENG type cam (cmos I presume...).

This is a better link to the Teledyne DALSA site info : Falcon2 Cameras (http://www.teledynedalsa.com/mv/products/cameras/family.aspx?fam=Falcon2)

I was ready to buy an HPX-250, but I now wonder of the Canon XF-300 would be a better choice, or if I should just wait a while longer and see what else comes out. I am very comfortable with the P2 workflow and Edius 6. Switching to a new file system is not something that sounds like fun. I really like the results that I get with my HPX-170, so I may wait a bit and see what others say about the HPX-250.

One thing about 50mbps long-gop on the XF300 is that you'll be getting a lot more recording time per GB of storage than AVC-I (depending on noise and scene complexity/motion).

I don't know if this has been discussed before: is the lens on the 250 parfocal? This is a big big problem on my 170! Zooming in and out looses focus. I'm never again buying a camera that can't retain it's focus. At least not an 1/3 chip camera with a servo focus ring that can't retain focus... Having a biger chip camcorder with a folow focus is a differnt thing.

But this small chip cameras with their small and useless LCDs and viewfinders and also their awful servo focus rings... I'm just furious as I was just watching some footage from today's talking heads shot where there are some parts out of focus, just because the cameraman zoomed out from a CU to a semi medium CU.

Sounds like your lens was not working properly. Just because it is part of the camera doesn't mean it is working as intended. I would ask Panasonic to check it out.

A German website published a test on the HPX 250

http://www.slashcam.de/artikel/Test/Panasonic-AG-HPX250EJ.html

Actually the first 'real test' I could find so far. Did anybody find another test - or even a comparison with the xf 300?

After reading everything I could find on the XF-300, it seems that it produces very sharp clear images at 1080p, but there are reports of markedly degraded performance at 720p. Since I use 720p 60 fps regularly, I have decided to go ahead and take my chances with the HPX-250. Once it arrives I will do some real-world testing of the rolling shutter and report back here.

After reading everything I could find on the XF-300, it seems that it produces very sharp clear images at 1080p, but there are reports of markedly degraded performance at 720p. Since I use 720p 60 fps regularly, I have decided to go ahead and take my chances with the HPX-250. Once it arrives I will do some real-world testing of the rolling shutter and report back here.

I would really appreciate if you could test the focus between different focal distances - zooming in and out and see if the focus stays on the spot.

I might have discovered the combination which seemed to produce the results you talk about. I was playing with the camera today at B+H to see if i wanted to buy one. I was using manual zoom but the camera was in autofocus. When I manual focused the lens but with autofocus on with lens zoomed all the way in and then zoomed out and zoomed in back to the original the subject very was out of focus. I thought this fit your issue. The camera was pretty slow in autofocusing when zoomed in and there wasn't much hunting so it didn't seem like it was in Autofocus. When in Manual Focus the focus held like it should.
I still haven't made my mind up about the camera but I did feel the lens was very sharp and held its back focus if in manual focus. Not so good in Auto focus




I don't know if this has been discussed before: is the lens on the 250 parfocal? This is a big big problem on my 170! Zooming in and out looses focus. I'm never again buying a camera that can't retain it's focus. At least not an 1/3 chip camera with a servo focus ring that can't retain focus... Having a biger chip camcorder with a folow focus is a differnt thing.

But this small chip cameras with their small and useless LCDs and viewfinders and also their awful servo focus rings... I'm just furious as I was just watching some footage from today's talking heads shot where there are some parts out of focus, just because the cameraman zoomed out from a CU to a semi medium CU.

When in Manual Focus the focus held like it should.


That's all I needed to hear! Thank you for the info!:)

About the autofocus, my thoughts: if you zoom out the framing changes. To me it sound obvious that the autofocus would change it's focusing point... There could be something in the foreground that you eliminated when you zoomed in or just the change in the composition made it necessary to change focus.

After reading everything I could find on the XF-300, it seems that it produces very sharp clear images at 1080p, but there are reports of markedly degraded performance at 720p. Since I use 720p 60 fps regularly, I have decided to go ahead and take my chances with the HPX-250. Once it arrives I will do some real-world testing of the rolling shutter and report back here.
Recording to a format that requires scaling, such as shooting 1080p on a 720p cam or vice-verse will usually result in a degraded image on any camera, or are you saying that the scaling on the XF300 isn't very good in particular?

That's all I needed to hear! Thank you for the info!:)

About the autofocus, my thoughts: if you zoom out the framing changes. To me it sound obvious that the autofocus would change it's focusing point... There could be something in the foreground that you eliminated when you zoomed in or just the change in the composition made it necessary to change focus.

Hey Sanjin,
Your welcome. Of course Auto focus will change to what it thinks you want to focus on. The slowness of the lenses focusing on the center target at the long end of the lens was surprising and completely in contrast to how fast it refocused (usually to infinity according to the viewfinder readout) when zoomed out and nothing was in the foreground. Could make you think the lens wasn't backfocused

The slowness of the lenses focusing on the center target at the long end of the lens was surprising and completely in contrast to how fast it refocused (usually to infinity according to the viewfinder readout) when zoomed out and nothing was in the foreground. Could make you think the lens wasn't backfocused

Hm... Don't know that much about lenses. Is it in any way harder for a lens to focus when zoomed in than in wide angle?

Konstantin - I have no personal knowledge of the XF-300, but several owners have expressed concern over the quality of the image in 720p. I believe that some of these reports are on this forum under the XF-300 thread.

Recording to a format that requires scaling, such as shooting 1080p on a 720p cam or vice-verse will usually result in a degraded image on any camera, or are you saying that the scaling on the XF300 isn't very good in particular?
Downconversion will almost certainly be more difficult than upconversion. The reason is that unless done in a very sophisticated manner, the fine detail captured by the 1920x1080 sensor will act to give aliasing on the downconvert. With upconversion, that's a problem that doesn't exist - but the upconverted signal won't be any sharper than what's present in the 720 signal.

What this means is that 1920x1080 imagers will give sharper (1080) pictures - but worse performance when downconverted to 720. It's quite likely that the 250 will be just as bad as the XF300 - purely down to it also having 1920x1080 sensors.

In the past (with 960x540 sensors) it's not been a problem for Panasonic - since although cameras like the HVX200 first make a 1080 raster, the real definition within that is somewhat below 1280x720. Then do the downconversion to 720 and there is no fine detail there to give the aliases!

Mark - if you're thinking of choosing the camera largely on the basis of 720p abilities, I doubt the 250 will be any better than the XF305. It's more likely to be worse, based on cost and "you get what you pay for". I'd certainly check it out before parting with any money.

Also worth thinking of the EX1, which does seem to be proven to do the downconvert pretty well. Alan Roberts tested it for the BBC, and his report concludes "the downconversion appears to be a little asymmetric, but in an acceptable way.......... It is highly unusual to see such good downconversion in a camcorder." See http://downloads.bbc.co.uk/rd/pubs/whp/whp-pdf-files/WHP034_ADD30-rev1-Sony-PMW-EX1-and-EX3.pdf

And looking at the 720p downconvert zone plate, (Fig 6 of his report) I fully agree.

It's worth mentioning that the downconversion may be influenced by such things as detail enhancement settings. Poor performance may be down to setup as well as the camera itself.

In the past (with 960x540 sensors) it's not been a problem for Panasonic - since although cameras like the HVX200 first make a 1080 raster, the real definition within that is somewhat below 1280x720. Then do the downconversion to 720 and there is no fine detail there to give the aliases!


I can't say I agree with you on that one. My HPX171 aliases much more when set to 720p. I'm actually quite annoyed by this. And it's also the reason why I shoot 720 only when there is a desperate need for tape time...

I can't say I agree with you on that one. My HPX171 aliases much more when set to 720p. I'm actually quite annoyed by this.
Downconversion is highly likely to cause aliasing - it's a question of how much. Starting with an image with less fine detail is better in principle, that's not to say there won't be any at all. And the 250 will give far more fine detail in the 1080 picture (to most people that's a big advantage for it!), so if the 171 has given problems in the past, it doesn't bode well for the HPX250 in 720 mode. I doubt it will be any better than the XF305.

One thing I did neglect is that whilst the 960x540 chips should give luminance detail up to about 1175x660, DVCProHD only records a 960x720 raster - so the horizontal downconversion is to 960 - not 1280. Hence more likelihood of horizontal aliasing from the downconvert than vertical.

I'm also wondering more about how much the complaints reported about 720p aliasing in the XF305, and Alan Roberts good assessment of the EX1, are down to settings. It does seem Alan may have brought the detail down from factory default - maybe the XF305 users had it set to a higher level? So less a camera issue, more one of bad setup?

The HPX 250 is now fully BBC approved for HD production in house and by indie production companies!

The HPX 250 is now fully BBC approved for HD production in house and by indie production companies!

Is there a report from Alan Roberts?

Is there a report from Alan Roberts?

Have asked Alan if he has had a look at it yet but if the BBC have approved it he probably has.

HD Magazine - HD Mag - Panasonic's 'Third Inch Sensor' HPX250 Gets BBCApproval (http://www.definitionmagazine.com/journal/2011/12/2/panasonics-third-inch-sensor-hpx250-gets-bbc-approval.html)

I also got notification today from panasonic europe.

P.S

Alan has informed me that he hasn't tested the camera and it was approved by the BBC on the basis that the regarding sensors and recording codecs are identical to two other cameras that he has already tested and I assume these to be the HPX371 and 301 .

P.S

Alan has informed me that he hasn't tested the camera and it was approved by the BBC on the basis that the regarding sensors and recording codecs are identical to two other cameras that he has already tested and I assume these to be the HPX371 and 301 .

Interesting. Surely they will do a test of the camera? They can't just give it an Okey based on the specs... Because that's what this seems like to me.

This "BBC APPROVED" seems like more of a commercial stunt to me lately...

Interesting. Surely they will do a test of the camera? They can't just give it an Okey based on the specs... Because that's what this seems like to me.

This "BBC APPROVED" seems like more of a commercial stunt to me lately...

NO it is nothing to do with a commercial stunt at all, the camera has the same sensor and the same on board codecs and most of the spec as the HPX371 so the BBC have decided that it will be acceptable based on that data and it is nothing to do with anything commercial or being a stunt at all. I formed the same conclusions when the 250 was released and it is now my B-camera for multi cam shoots.

Take it as you wish but if you do your own research like I have done you will see beyond the commercial hype and bullshit of a lot of the twaddle written on forums like this and see what kit is really acceptable and what kit is camera bashing from people who A: have never seen it B: work for manufacturer s,c or red or C: don't even work in pro video and make test video's for a living in the hope that p, c, s or red will give them some exclusive access.

It's approved as is the 371 as is the 1/3" camera's from canon but the codec is the key to all of those and not just sensor size or lens servo from test cameras!

If you are not happy with that then buy something else or do your own tests and if you want a large sensor camera with a broadcast acceptable codec then mr C has just released one and if you wait you may be a happy bunny albeit at a cost far more than a 250 or 371!

P.S Have you bothered to do any tests yourself? I suspect not so please don't bash our public organisations that have nothing to do with commercial manufacturers that pay people like Alan and take the time to do it all for us all for free due to public access! I asked Alan a direct question re the 250 and he gave me as usual a very honest and rapid response that as always has nothing to do with commercial stunts but is totally based on fact and logical reason.

I think we have all been very lucky to get independent reports on all the cameras the BBC test and they are all based on fact and not any commercial aspects, the BBC have also approved cameras such as the AF101, the F3 and other sony camera's but they also need external recorders to attain full broadcast codec spec so at the end of the day we as users should cherish that and make our decision based on out own needs not totally on any singular report. Certainly I have and chose the HPX301/371 nearly three years ago and have not regretted going down the P2 route after several years with sony cameras and have now added the 250 based on my own experience over that time regardless of a further BBC report!

Do the slovenian national broadcaster do their own tests? LIke all the others inc the commercial broadcasters here in the UK I suspect not, so if the BBC says a camera is approved I think we should think ourselves very lucky that they get Alan to do these tests for us and allow us to make our own conclusions that can be commercial but certainly I see the BBC as a valuable independent resource for such tests that have little to do with manufacturers or commercial gain.

Garry I must have put myself wrong. I certainly didn't won't to say all the things you accused me of saying.

I wanted to say that the manufacturers are using this "BBC approved" for commercial reasons. Particularly I had Canon in mind and their XF300 cameras. Not to bash on the cameras, I had it on a shot last time and I really like it.

And I certainly understand why they would give the 250 a green light before even putting it through the paces.
But it's still a small form camera with quirks that small form cameras usually have. And that's why it surprises me that they just gave it a go. Yes, I get it: they gave it's picture a go based on the codec and on the familiarity with the 370. But still, they didn't test it! What if it also has ghosting on the pap2 setting (is it pap2?)? Or how many resolution does it have? Or how is the CA? Or how does it perform under...? I'm certain they won't be buying any before doing some test. And if this institution becomes a legitable benchmark for judging camera performance (which it already is basically) it's going to become something that the companies are going to exploit and put pressure on for their cameras to get approved also. I'm just thinking here - not accusing anybody of anything.

As for mr.Roberts, I appreciate he's work! And I'm not bashing you public organisation, I'm bashing (if any) on the people that use this BBC approved for commercial reasons. And even these people have the right to do so. There's just all this talk on the forums and people here in Slo. that aren't any experts just some lazy/"smart as hell" people that I have to deal on a daily basis that are saying: "but the xf300 is BBC approved, you know...!" -> this is what's bothering me:)

And no I haven't used or even held the 250. Wish I could, but no reseller has one here as of yet:(

Here in Slo. and Cro. material from my HPX171 is perfectly acceptable for broadcast:)

OK I take your points but the BBC ( and Alan) work very hard with the manufacturers and contact that we do not have privy to takes place, the manufacturers are also given a chance to reply to any reports and also agree with the BBC that they can be put into the public domain.

Camera's are mainly tested for technical standards and functionality is down to the camera dept and individual choice so you pays your money and makes your choices based on that not a BBC engineering report that approves it for broadcast chain use.

Companies are allowed to use the BBC approved list as are everyone who wishes to, I certainly do and it gives my clients confidence in my work but I appreciate that valuable bench mark and certainly don't use it as a marketing stunt! Canon and others may use it to sell product but that is up to them but you don't see arri or red needing to do it. If I were buying a small camera now I would chose the canon but I bought into the P2 system three years ago and now will stick with it as I can still chose 2/3" and 1/3" chip small and large cameras that all use the same codec and card storage.

As for the 250 it will have the same characteristics as the 371 and the BBC would have confirmed this with panasonic but it is approved so that is where we are, I don't think Alan does extensive operational tests and as said that is up to us to do after cameras are approved for use in the broadcast chain. There are others in the BBC who look at cameras from this perspective and only recently there was an open day up in glasgow for people to see what they thought about several cameras on the BBC approved list.

Specifically it will probably have the PAP2 problem but it may be better as that was fixed in firmware on the 371 with PAP1 and the CA is also addressed in the software on these cameras but I doubt if it will be worse than the 371 but it may also be better due to the fixed lens design, the BBC may or may not have confirmed this with panasonic.

A XYZ full HD camera may be acceptable for broadcast anywhere in the world but unless a broadcaster has tested it thru the full chain it may not meet the technical requirements of the BBC or any other broadcaster.

In some regions HDV is acceptable for HD but in others and for the BBC it is not so it is down to choice at the end of the day but you may have long wait before every camera and manufacturer is selling you exactly what you want to buy!