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    Senior Member toke lahti's Avatar
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    Quote Originally Posted by Barry_Green
    But 4:2:0 and 4:1:1 are fairly equivalent to each other.
    If you compare the amount of data, they are equivalent.
    If you compare them to human vision 4:1:1 has no sense at all.
    Just a relic from interlaced era.


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    Quote Originally Posted by ullanta
    What Bob is sensibly saying is that in the Panasonic case, we may describe a chroma position as a unique COMBINATION of R,G,B pixels. There may be some overlap, but each TRIO is unique and has some new color info.
    I see what's being said, and it's an interesting point. Engineering wise I'd think it to be a good way of doing things.

    But all I think it will do in practice is smooth out the changes, very comparable to increasing the image resolution of a picture in a photo editing program. That will also seem to look better because it's less 'steppy' - but does not, can not, increase actual resolution. Same here.

    Is this relevant to the real world? Only noticeably in certain cases probably, and chroma key being the most obvious, I'd say. Imagine a black horizontal bar against the green screen background, such that if you read out the values of green pixels 2=full signal, 0=no signal. If we read out a vertical column of the 540 green pixels, we may get: 2,2,0,0,2,2 etc. (Guess where the bar is!?!)

    If we wanted 1080 pixels in total, we could simply repeat each one, so: 2,2,2,2,0,0,0,0,2,2,2,2. What Bob is saying (which I think is what does happen) is that the interpolation would give us something like 2,2,2,1,0,0,1,2,2,2,etc - smoothed, but no extra detail. Whereas 1080 real pixels may pick up a crack in the bar and give 2,2,2,0,2,0,0,0,2,2,2,etc say. Unlike the interpolation, they have found real extra detail.

    Coming back to the real world, Panasonics approach I consider in principle to be a very good engineering compromise in designing a 1/3" HD camera. What I don't believe it can do is deliver more than 540 lines of real vertical colour resolution. If anybody can think of a mechanism whereby it can, I'd be very interested to hear it.
    Last edited by harddrive; 02-28-2006 at 05:04 AM.


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    Senior Member esperman's Avatar
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    Quote Originally Posted by Justyn
    I'd also like to relay a story that my friend told me about a shoot he just did. He does high-end audio and video assist on 35 and HD shoots here in Town. Big ones, like he just did a disney commercial with Antwon Fuqua (sp).. Spike Lee, Adidas.. and all that jazz.

    Well he's also the one who took my place in line when the HVX came in and the other day he brought it to a cinealta shoot that he was providing video assist for. He was doing it to let the coordinator see the camera.. and just start to show it off as he aims at being able to rent it out on these cinealta and varicam shoots as a potential B camera.

    Well, in his honest assesment, he was shooting some side by side stuff and was blown away at how similar the images look, and quite often he said that he tought his footage looked even better than the Cinealta. He then got the director's attention who came over to check out his footage.. then more than a few times came back to A and B the cameras... With the growing wrath of the DP who owned the Cinealta.. and how after a while the director took his card... then asked where he kept it so he could sneak in and steal it... then after lunch break.. he'd worked his way into shooting on the commercial for the next day with his camera.

    Now, I know a lot of commercials want the big form cams on the dolly...and that the cinealta is of course a better camera... but the HVX impresses professionals. My buddy said the director went off to consult with the producer about the possible angles that this small form camera will offer. It's so much of a difference in size and mass... that the shortcomings are clearly overshadowed by what else it can offer.

    So, given that I can't understand a whole heaping lot about this camera.. I know that when we had it shooting at a concert the other night.. with the Dell 2405 pumping out it's image... we had a friggin swarm of people over there going nuts over the image.
    Exactly what I've been saying. The image is impressive anyways...and gets real impressive when you see what originates it. This camer rocks.


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    Now I think an HVX Andromedized will be worth the price. Juan we are patiently waiting.


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    I wanted to try to help clear up some of the things I said in the thread. This may get a bit technical... so be forewarned.

    When I spoke about 4:2:0, I was speaking about the USA form of 4:2:0, where the color information changes every 2 scan lines.

    With 1080 lines, a 960x540 CCD must have every other scan line as interpolated. This does NOT add any new information to the image, but it does smooth any rough edge in the color information. In 1080 mode, it looks like this:
    ...
    Scan Line 100: New Green, Interpolated Red & Blue
    Scan Line 101: Interpolated Green, New Red & Blue
    Scan Line 102: New Green, Interpolated Red & Blue
    Scan Line 103: Interpolated Green, New Red & Blue
    Scan Line 104: New Green, Interpolated Red & Blue
    Scan Line 105: Interpolated Green, New Red & Blue
    ...
    This is NOT as good as having new Green, Red, and Blue information on every scan line (true 4:2:2), but is better than repeating the same color information for 2 scan lines (USA 4:2:0).

    In zooming into different still images of HVX in 1080 mode, I can't find any color problems due to their native CCD resolution and DSP. The exception is one green screen shot, which had glitches due to a codec problem. The problem was the conversion to another format and NOT the fault of the HVX.


    You can see several 10x stills from different images in the following message:


    http://www.dvxuser.com/V6/showthread.php?t=47914



    Bob Diaz


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    Quote Originally Posted by BobDiaz
    This is NOT as good as having new Green, Red, and Blue information on every scan line (true 4:2:2), but is better than repeating the same color information for 2 scan lines (USA 4:2:0).
    But isn't a more fair comparison to have the missing lines in the 4:2:0 case be interpolated instead of repeated? If interpolation makes sense in the pixel shifted case, wouldn't you use it in the non-pixel shifted case as well? Agree the offsetting of the green might result in smoother interpolation, but the same *amount* of interpolation is happening in both cases, isn't it? I am curious as to how quantifyable the resulting chroma benefit is.

    Thanks for the pointer to the green screen thread -- interesting.


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    Quote Originally Posted by BobDiaz
    This is NOT as good as having new Green, Red, and Blue information on every scan line (true 4:2:2),
    All fully agreed.
    .........but is better than repeating the same color information for 2 scan lines (USA 4:2:0).
    Well - only if you're using the information directly as such. But surely if the keyer or whatever makes use of the 4:2:0 data via interpolation (as it should), it all comes out the same? Panasonics approach makes life simpler later in the chain, as it interpolates early on, then records the interpolated samples. The disadvantage to this approach is that bitrate gets used up recording interpolated samples - surely (in this idealised discussion) it's far more efficient in bandwidth terms to record 4:2:0 and then interpolate, rather than interpolate and then record 4:2:2?


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    The Professor BobDiaz's Avatar
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    As I tried to find images to prove or disprove my point, that the sharp edges of objects in 1/3" CCD images do not exist. Sorry, but 1/3" CCDs just do not provide full 1080 detail. What I see in the 10x views from the Canon and Panasonic are slightly fuzzy transistions from one edge to another.

    In the case of the Panasonic, the transistion is smooth. In the case of the Canon, it can be rough, BUT yes there is software that can smooth out the color information making it a smooth transistion. Would it be as good as the Panasonic? I can't be sure until I see results.

    Here is a 10x zoom green screen shot from the Canon:





    Here is a shot from the HVX that I've pulled a 10x zoom from the right side of the face with something green in the background.




    Here's the whole image in context; I reduced the size of the image to fit nicely within this message.




    As seen cropped, look closely at the edge this is shown 1x size:




    The background is a bit out of focus, but the edge of the face looks clean without any roughness to it.


    I wish we had 2 exact same shots, one with the HVX green screen and the other a Canon green screen. Might be interesting to compare the final keyed results to see if there's any real difference.

    Real World Tests ---> <--- Theory
    You may find Part 3 interesting to read; see below:

    http://www.coax.tv/ListOfIssues.htm#larrythorpe


    While he does not get into color issues, he does talk about resolution.


    Bob Diaz


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    Senior Member toke lahti's Avatar
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    Quote Originally Posted by johncordell
    But isn't a more fair comparison to have the missing lines in the 4:2:0 case be interpolated instead of repeated? If interpolation makes sense in the pixel shifted case, wouldn't you use it in the non-pixel shifted case as well?
    With 4:2:0 you only have one chroma component sample per 2x2 pixels. There's no room for interpolated sample.
    If 4:2:0 is converted to 4:4:4 (eg for cc or fx) then its up to decoder how well it interpolates the missing values.
    Pixel shifting is two-bladed sword. On the other hand we get more luma resolution (but with lesser MTF) with real world images with all the colors in them. But in the trade off we loose chroma resolution in special situations like chroma key.
    More calculated luma samples, but all a bit blurry and all calculated chroma pixels a bit blurry. Because every YCbCr pixel has interpolation in it.
    Think about shooting a black object with green background. Or red, blue and black. Suddenly pixel shift advantage is all gone and all you have is 960x540 from which you have to substract Kell factor so you have only about 750x400. This is way lower than what chroma resolution camera records (1080p: 640/720x1080 720p: 480x720). Actually chroma resolutions that camera head produces and storage part records are upside down. So in the end there will be only 640/720x400 (1080p) or 480x400 (720p) in these cases. So we are quite far from what real fullHD 4:2:2 chroma would be (960x1080).

    Once again I have to say that 4:2:0 would be more optimal chroma resolution for this camera when shooting progressive with square pixel luma resolution (1280x720).

    Another thing with pixel shift is decreased "dynamic resolution" when there is movement in the picture. After all we are shooting moving pictures. But I don't think that's such a bad issue because human eye's resolving power also decreases with movement and there's also motion blur involved with moving objects.

    Could somebody explain why this "dynamic resolution" decreases with pixel shift?
    I haven't fully understood this yet.


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    Senior Member toke lahti's Avatar
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    Quote Originally Posted by toke lahti
    Could somebody explain why this "dynamic resolution" decreases with pixel shift?
    Please, somebody, educate me?
    I suppose Steve Mullen does not chat here?


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