Re: Varicam or HD

[Jef Huey <jhuey(at)henninger.com>]

Victor,

Like I said, ignore pixel count FOR THE TIME BEING.

4:2:2 and 3:1:1 is about how much information EACH pixel has.  It has 
nothing to do with how many pixels are on a line.

1920 x 1080 is a description of how many pixels wide by how many pixels 
high an HD image is.

Each of those pixels could have been captured as EITHER 4:2:2 or 3:1:1.

Do you see what I am talking about here?   So no, a 300x300 4:4:4 image 
is not better than a 1920x1080 4:2:2 image.
But the individual pixels of the 300x300 have more color information 
EACH than the later image.  And you  would get a better key from the 
300x300 image.

At least that is how I understand it.   ;)    All this said, testing is 
and good lighting is the key.  PUN!!

Jef


Victor Wolansky wrote:

> Mmmm.. I'm not sure if I can ignore pixels count on a digital image.. that is like saying that a 300x300 4:4:4 image is better than a 1920x1080 4:2:2
>
> I think I have to try it to have a better idea of what is really the best thing. This is only numbers :-)
>
>
> ________________________________
>
> From: owner-ds(at)Softimage.COM on behalf of Jef Huey
> Sent: Mon 8/1/2005 2:15 PM
> To: DS(at)Softimage.COM
> Subject: Re: Varicam or HD
>
>
>
> Victor,
>
> I agree - more pixels = more resolution. BUT ...
>
> What we are also talking about in a discussion of 4:2:2 vs 3:1:1 is how
> accurately each pixel describes the image in front of the camera.
>
> In 4:2:2 there is a greater COLOR resolution in each pixel. More
> subtlety. And that is the "key" (pun intended) to keying. Ignore number
> of pixels on a line for the time being. That is picture size. Think
> about the quality of the description that each pixel gives you when it
> comes time to do a key.
>
> Do you follow me there?
>
> Jef
>
>
>
>
> Victor Wolansky wrote:
>
>  
>
> > Well what we can tell from the numbers is that seems that the HDCAM
> > and VARICAM have the same horizontal color information, 480 pixels,
> > but HDCAM have more luma information that VARICAM, 1440.
> >
> > What I can tell by my little research now is that if you can not
> > digitize HDCAM SR, and want something better than HDCAM or VARICAM,
> > then you can connect you HD-SDI output of the camera to a Deck like a
> > D5, D6, or HDCAM-SR in which case I will have a full sampled 1920:960:960
> >
> > That is my understanding but I could not find yet information to
> > confirm this. Any one knows?
> >
> > I don't think we are comparing apples and oranges, it is an absolute
> > thing, more pixels.. more information.. the keyer will have more info
> > to do his job. If we compare format to format, VARICAM have more color
> > info per pixel, but less total information per line, what can be the
> > bad thing about having more horizontal luma information, I think that
> > can't be bad.
> >
> > Just my opinion.. I can be completely wrong...
> >
> > Victor Wolansky
> >
> > DS VFX Artist
> >
> > WEBsite <http://www.e3post.com/>
> >
> > Demo Reel <http://www.e3post.com/reels/victorreel.html>
> >
> > 815 Slaters Lane
> >
> > Alexandria. VA.
> >
> > 443-797-3507
> >
> > -----Original Message-----
> > From: owner-ds(at)Softimage.COM [mailto:owner-ds(at)Softimage.COM] On Behalf
> > Of swaffordt(at)bellsouth.net
> > Sent: Monday, August 01, 2005 8:42 AM
> > To: DS(at)Softimage.COM
> > Subject: RE: Varicam or HD
> >
> > Jeff... great information, thanks... btw, your reel rocks!
> >
> > TBONE
> >
> > -----Original Message-----
> >
> > From: owner-ds(at)Softimage.COM [mailto:owner-ds(at)Softimage.COM] On Behalf Of
> >
> > Jef Huey
> >
> > Sent: Monday, August 01, 2005 10:26 AM
> >
> > To: DS(at)Softimage.COM
> >
> > Subject: Re: Varicam or HD
> >
> > My gut instinct about this analysis is that it has its own flaws.
> >
> > It seems to be one of comparing apple and oranges.
> >
> > Alot of the numbers are base on totals per line. I think that is not
> >
> > valid when it comes to blue screen work. What matters there is color
> >
> > resolution of each Pixel, not the total for a line. The keyer must make
> >
> > decisions about what is "Green" and what is not. If color of each
> >
> > pixel is sampled at a higher resolution (4:2:2), then you will be
> >
> > better off. That is why 4:4:4 RGB keys are so desirable.
> >
> > At least that is how I am reading it and I definitely do NOT have a math
> >
> > head.
> >
> > Where did this info come from - Sony maybe ;) ?
> >
> > Jef
> >
> > Victor Wolansky wrote:
> >
> >    
> >
> > > *I found this searching on this topic, I think is very useful
> > >      
> > >
> > > information to share..*
> > >      
> > >
> > > * *
> > >      
> > >
> > > * *
> > >      
> > >
> > > *Riddle#2: Does the Varicam have more Color Space than the F900?
> > >      
> > >
> > > Is the Varicam better for green and blue screen matting?*
> > >      
> > >
> > > What I'm discovering is a bit of an eye opener in terms of Color Space
> > >      
> > >
> > > and Image Sampling between the Sony CineAlta and the Panasonic Varicam.
> > >      
> > >
> > > Have you heard the common misconception, prevalent across the
> > >      
> > >
> > > industry, that the Varicam records a 4:2:2 color space to tape? The
> > >      
> > >
> > > argument goes like this ...... while the Varicam has less resolution
> > >      
> > >
> > > in luma, it has more resolution in chroma compared to the Sony F900
> > >      
> > >
> > > CineAlta. So this means the colors are sharper, therefore the over all
> > >      
> > >
> > > image will tend to look relatively sharper as well, despite there
> > >      
> > >
> > > being less pixels in total compared to the F900. Consequently, this
> > >      
> > >
> > > helps the Varicam produce an image that looks just as sharp as the
> > >      
> > >
> > > F900. While the images are indeed amazingly similar, this reasoning is
> > >      
> > >
> > > bogus.
> > >      
> > >
> > > And if this were true, then the Varicam might turn out to be the
> > >      
> > >
> > > better tool for doing green and blue screen work. On the face of
> > >      
> > >
> > > things, it might seem the Varicam will do a better job with pulling
> > >      
> > >
> > > mattes with double the color resolution. After all you are keying to a
> > >      
> > >
> > > color, and if the colors are sharper, then it should work better -
> > >      
> > >
> > > right? Again, this reasoning is bogus. The real story is a little more
> > >      
> > >
> > > involved, as I will try to explain.
> > >      
> > >
> > > It is amazing how entrenched the misconception is that the Varicam has
> > >      
> > >
> > > approximately double the color space of the F900. But in a sense this
> > >      
> > >
> > > is true ..... it all depends on how you look at it! Lets start by
> > >      
> > >
> > > looking at precisely how each HD camcorder system processes and
> > >      
> > >
> > > records its images to tape. But in so doing, we can't lose sight of
> > >      
> > >
> > > the fact that the starting point for each camcorder is different. The
> > >      
> > >
> > > Sony CineAlta has approximately twice the number of pixels per CCD
> > >      
> > >
> > > compared to the Panasonic Varicam (2.2 megapixels for the F900 verses
> > >      
> > >
> > > 1 million pixels for the Varicam).
> > >      
> > >
> > > The first step in both cases is pre-filtering in luma. Both systems
> > >      
> > >
> > > use the same reduction factor, namely 1.33^* (recurring). The F900
> > >      
> > >
> > > starts with 1920 pixels per line, and filters down to 1440 in luma
> > >      
> > >
> > > (1920 divided by 1.33 = 1440). The Varicam starts with 1280 pixels per
> > >      
> > >
> > > line, and filters down to 960 in luma (1280 divided by 1.33 = 960).
> > >      
> > >
> > > The original "1920", and the original "1280", are defined by their
> > >      
> > >
> > > respective format specifications.
> > >      
> > >
> > > Next, chroma is sampled at 3:1:1 in the case of the Sony camcorder,
> > >      
> > >
> > > and at 4:2:2 in the case of the Varicam camcorder. So the CineAlta has
> > >      
> > >
> > > 1440 in luma and (1440/3)= 480 in chroma, while the Varicam has 960 in
> > >      
> > >
> > > luma and (960/2) = 480 in chroma. Note that both systems now have
> > >      
> > >
> > > precisely the same number of pixels per line, namely 480, representing
> > >      
> > >
> > > color information!!!
> > >      
> > >
> > > Just to be clear about the mathematics I used here, the divisors 3 and
> > >      
> > >
> > > 2 respectively, come from the how each camcorder subsamples its color
> > >      
> > >
> > > space. The CineAlta is 3:1:1, so it subsamples its chroma channels by
> > >      
> > >
> > > a factor of 3 in relation to its luma channel. Specifically, it
> > >      
> > >
> > > samples chroma at 1/3 (one third) that of the luma channel. So this is
> > >      
> > >
> > > why I divided by 3. The luma is sampled at 1440 /3 = 480 which is the
> > >      
> > >
> > > chroma sampling. Similarly, the Varicam is 4:2:2, so it subsamples its
> > >      
> > >
> > > chroma channels by a factor of 2 in relation to its luma channel.
> > >      
> > >
> > > Specifically, it samples chroma at 1/2 (one half) that of the luma
> > >      
> > >
> > > channel. So this is why I divided by 2. The luma is sampled at 960 /2
> > >      
> > >
> > > = 480 which is the chroma sampling.
> > >      
> > >
> > > While both systems (coincidentally) have equal chroma resolution, the
> > >      
> > >
> > > Sony HDCAM has 50% more luma resolution. This is not surprising
> > >      
> > >
> > > considering it started out with twice the number of pixels in the
> > >      
> > >
> > > first place.
> > >      
> > >
> > > Another way to look at this is as follows:
> > >      
> > >
> > > HDCAM = 1440 in luma, and (1440 /3) = *480* in chroma = 1440:480:480 =
> > >      
> > >
> > > 3:1:1
> > >      
> > >
> > > HD Varicam = 960 in luma, and (960 /2) = *480* in chroma = 960:480:480
> > >      
> > >
> > > = 4:2:2
> > >      
> > >
> > > In an absolute sense, the CineAlta and the Varicam have identical
> > >      
> > >
> > > color space i.e. *480* pixels per line!!!
> > >      
> > >
> > > But relatively speaking, the Varicam samples a slightly lower
> > >      
> > >
> > > resolution image at a slightly higher rate for its colors.
> > >      
> > >
> > > "A-little-more-of-a-little-less" means there is no net gain in terms
> > >      
> > >
> > > of color space compared to the CineAlta. However, the CineAlta has a
> > >      
> > >
> > > comparative advantage in terms of resolution in luma (or the black and
> > >      
> > >
> > > white component of the image) by a factor of a half i.e. 50% more
> > >      
> > >
> > > resolution in luma. Or 1440 pixels compared to 960 pixels
> > >      
> > >
> > > (mathematically speaking: 960 x 50% = 480, then 480 + 960 = 1440) (or
> > >      
> > >
> > > 960 x 150% = 1440) (or 1440/150% = 960) etc.
> > >      
> > >
> > > Sony's 3:1:1 exactly equals Panasonic's 4:2:2 in terms of color space
> > >      
> > >
> > > in an absolute sense. But in respect to the Varicam's own inherent
> > >      
> > >
> > > line resolution, it has twice the rate of color sampling compared to
> > >      
> > >
> > > the CineAlta. This leads to the conundrum that it is true to say the
> > >      
> > >
> > > CineAlta and the Varicam have identical color space, but at the same
> > >      
> > >
> > > time, it is also true to say the Varicam has twice the color space of
> > >      
> > >
> > > the CineAlta. This is of course is contradictory.
> > >      
> > >
> > > The truth of the matter can only be resolved when you look at the
> > >      
> > >
> > > total number of pixels per line that are sampled for color information.
> > >      
> > >
> > > **3:1:1 color sampling of 50% more line resolution = 4:2:2 color
> > >      
> > >
> > > sampling of 50% less line resolution.**
> > >      
> > >
> > > To complete the story, both camcorders sample at 10 bit, pre-filter,
> > >      
> > >
> > > compress, and record to tape at 8 bit. In other words, both systems
> > >      
> > >
> > > work in a very similar way, and indeed, they both produce very similar
> > >      
> > >
> > > looking images.
> > >      
> > >
> > > Many people believe that the Varicam performs better for green and
> > >      
> > >
> > > blue screen matting processes, compared to the Sony F900. I think the
> > >      
> > >
> > > reality is that they are about the same in their blue and green-screen
> > >      
> > >
> > > matting capabilities.
> > >      
> > >
> > > Just as an aside, the Sony HDCAM (D-11) compression scheme is based
> > >      
> > >
> > > upon a 1440 x 1080 image format and 3:1:1 chroma subsampling, as
> > >      
> > >
> > > described above. Downsampling is required upon compression, and
> > >      
> > >
> > > upsampling is required upon decompression. The downsampling inherent
> > >      
> > >
> > > in HDCAM compression of 1080i or 1080p means that luma sample aspect
> > >      
> > >
> > > ratio is effectively 4/3 (and chroma subsampling is equivalent to
> > >      
> > >
> > > 4:1:1) relative to the original 1920x1080 image array. So luma is
> > >      
> > >
> > > multiplied by 4/3 or 1.33^* (recurring) i.e. 1440 multiplied by 1.33^*
> > >      
> > >
> > > = 1920. Hence it is 3:1:1 color space in respect to 1440 x 1080, but
> > >      
> > >
> > > really only 4:1:1 color space in respect to the originally captured
> > >      
> > >
> > > 1920 x 1080, and also the 1920 x 1080 produced after decompression of
> > >      
> > >
> > > the signal and upsampling. In some ways it is hokus pokus with numbers
> > >      
> > >
> > > to say HDCAM is 3:1:1, as 4:1:1 is perhaps more accurate in its
> > >      
> > >
> > > practical application. Same with the Varicam, it is 4:2:2 color space
> > >      
> > >
> > > in respect to 960 x 720. This leaves us with the somewhat awkward
> > >      
> > >
> > > ratio of 4:1.5:1.5, which is the color space in respect to the
> > >      
> > >
> > > originally captured 1280 x 720, and also the 1280 x 720 produced after
> > >      
> > >
> > > decompression of the signal and upsampling.
> > >      
> > >
> > > Victor Wolansky
> > >      
> > >
> > > DS VFX Artist
> > >      
> > >
> > > WEBsite <http://www.e3post.com/>
> > >      
> > >
> > > Demo Reel <http://www.e3post.com/reels/victorreel.html>
> > >      
> > >
> > > 815 Slaters Lane
> > >      
> > >
> > > Alexandria. VA.
> > >      
> > >
> > > 443-797-3507
> > >      
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