Canon's 24F and 60i modes explained

[Steve Mullen]

Using my math model that relates CCD resolution to measured resolution, I correctly predicted HVX200 CCD resolution to be 960x540. I've now used my model to try to understand 24F.

One key question is whether Canon uses the same or a different deinterlacing process than does Sony.

Contrary to everything I've seen, the Sony does NOT simply discard one field and "bob" interpolate a new 1080-line frame. If it did, it's CineFrame V. rez. would be only about 360 TVL -- not 540 TVL. (The Sony's 50i/60i measures about 720 TVL because of row-pair summation performed in the CCD.)

I believe a "2D FIR (Finite Impulse Response) filter" is applied to one of the fields as part of the deinterlace process. These filters can have a small or large number “taps” where each tap is a sample. Current filters (interpolators) have up to 1024 taps; which would support a 32x32 window around each target pixel. The filter vertically scales the 960x540 image to a 960x1080 frame. For static video, effective vertical resolution is increased by 150%. The result is 1080-line “interlace” video (without interlace artifacts) and with an effective vertical resolution of 540 TVL.

Because of Green pixel-shift, Sony static horizontal resolution is about 560 TVL/ph while dynamic horizontal resolution is about 535 TVL/ph. (Typical resolution is 550 TVL/ph.) {From Adam's measures.}

We have two sets of 24F numbers for the Canon: Adam's worst-case (wobulation) tests have 24F resolution at 800x540. And, Shannon's best-case STATIC 24F tests at 800x800.

These numbers cannot come from a Sony CF deinterlacer. But, they could come from a more advanced deinterlacer.

Canon’s 24F function likely uses frame-adaptive deinterlacing. The CCDs are interlaced scanned at 48Hz. Each scan yields a 540-line field that is sent to the deinterlacer where logic is used to measure the motion between fields.

When there is little or no motion, the H1 performs a “weave” interpolation where odd and even fields are simply combined into one 1080-line frame. Effective vertical resolution on a static test will be about 810 TVL.

When there is motion between fields, one field is discarded and the H1 performs a "bob" interpolation to generate a 1080-line frame. Effective vertical resolution will be about 540 TVL.

In order for this process to work as described, each scanned 540-line field must have a 540 TVL resolution. And, a frame must have 1080 TVL. Were row-pair summation DISABLED this is exactly the resolution that would be generated by interlace scanning. In 1080i60 mode, row-pair summation reduces effective vertical (frame) resolution to about 710 TVL.

Disabling row-pair summation should reduce sensitivity by 6dB (1 stop). That's not the case with the H1. In fact, sensitivity is slightly incrreased by the switch from a 1/60th shutter to a 1/48th shutter-speed. So although I can explain the deinterlacing process--I cannot understand how H1 interlace scans it's CCDs so as not lose 1-stop.

NOTE 1: Row-pair summation obtains 6dB gain because it "adds" pairs of CCD rows--typically within the CCD. Because the pairs of rows are in slightly different vertical locations, the "addition" acts as a spatial filter. If the rows were not in different locations, no resolution would be lost and yet 6dB of gain obtained.

NOTE 2: If the static resolution measures were wrong -- then there is no puzzle! Were the 24F vertical resolution about 720 TVL rather than 800 TVL, row-pair summation could be fine. (I see only 750 TVL from Shannon's chart.) Which is why it would be nice to have Adam's static measure of 24F. My model really needs measures from the the same chart.

NOTE 3: If we assume each incoming field has only about 360 TVL -- is there another deinterlacing model that yields 540 TVL (dymamic) and 800 TVL (static)? I'm VERY open to being wrong on HOW the deinterlacing is done.

Because of Green pixel-shift, for both 60i and 24F, static horizontal resolution is, in theory, up to 830 TVL/ph. The lens MTF and CCD MTF, plus the anti-aliasing filter appear to limit horizontal resolution to about 810 TVL/ph. My model's estimate, for both 60i and 24F, dynamic horizontal resolution is 800 TVL/ph.

By the way, my model now estimates with less than 1-pixel AVERAGE error the performance of ALL the low-cost HD camcorders, plus the VARICAM. (Pointers to additional HDCAM and CineAlta measures are welcome.)

[John Cordell]

Thanks Steve, I was hoping your expertise would weigh in on what's under the hood for 24f. Much appreciated.

[Barlow Elton]

Thanks Steve! I felt the winds from the east blowing pretty hard from that turbo propeller on top of your beanie workin' overtime to come up with that conclusion!

For a mere mortal such as myself, your model would seem to be accurate. The only thing I think you might have forgot to mention that makes 24F work is that the CCD's are likely clocked at 48hz for 24F. This is probably a crucial aspect of the mode that makes the motion look right. I've done a number of "smart deinterlaces" in converting 60i to 24p and they've never looked quite as good or consistent as 24F does.

Thanks again!

[Barlow Elton]

btw, Steve, I'm not sure how much time you've put behind the wheel of the H1 because every real-world shooting with an HD monitor I've done in a controlled environment showed to my human eyeballs that 24F is actually *slightly* more sensitive than 60i.

1/60th in 60i at F 2.0 and 1/60th in 24F at F 2.0 on a MacBeth chart doesn't show any perceivable difference in sensitivity. And if you swtich to 1/48th in 24F you get a little more sensitivity, which is what most people would shoot 24F at anyway.

I want to understand how industry professionals like Scott Billups and people at Cineform and FotoKem have publically used words like "awesome" to describe the quality of the H1 24F when transferred to film, and in direct comparison to the F900. If the H1 isn't resolving enough TVL for film outs and other high end purposes, then what's going on here?

Is it just not "progressive" enough to be useable?

http://cineform.blogspot.com/

[Robert Sanders]

I think we fall victim to catch words and tech phrases.

"It's not really really 'progressive'", therefore it must be bad.

The footage looks great. The resolution looks great. The motion looks great. The film outs look great. But it's not really really progressive.

I find many forums, threads and message boards to be very hostile toward Canon for some reason.

I guess I better grab a cup of coffee. I'm cranky this morning.

[Barlow Elton]

Originally Posted by Robert Sanders

I think we fall victim to catch words and tech phrases.

True dat.

"It's not really really 'progressive'", therefore it must be bad.

Funny, isn't it? No matter how good the result some want the security of a buzzword.

The footage looks great. The resolution looks great. The motion looks great. The film outs look great. But it's not really really progressive.

It's like..."it depends on what the meaning of the word IS is"

I find many forums, threads and message boards to be very hostile toward Canon for some reason.

Again, curious, isn't it? Either you have the MOJO of Panny or the ahh gee isn't it cool that JVC made a neat camera? You know, if Canon had something like SSE they would be CRUCIFIED and ridiculed by a good many that participate on the forums. Instead JVC gets treated with kid gloves, even by guys like Steve Mullen...and they're a MAJOR MANUFACTURER!!

Funny how Canon is perceived as a brand when it comes to video. There's a lot of love/hate rather than objective talk. I dunno, I just go by what I see and evaluate the images and the features, then debate the tradeoffs, then make my move.

Imagine if the HVX had SDI? Would it not be shouted from the mountaintops?

I guess I better grab a cup of coffee. I'm cranky this morning.

I made mine extra strong this morning. Only made me crankier.

[Barlow Elton]

https://i.cmpnet.com/dv/video/4cam-1080cams.mov.zip

I believe it's handling the weeble wobble fairly well.

[Robert Sanders]

Well Barlow, it's easy for you and I to be written off as sour grapes because we've made our decisions and placed our money on the H1.

Again, if there are some technical inferiorities to the camera then I'm willing to accept them. What I'm having difficulty with is the "tone" of the conversations in the H1 forums as opposed to the love fests elsewhere.

And you're dead right about the HD-SDI issue. It would've been universally heralded as brilliant forsight by Panasonic if it had been included in the HVX (same goes for the JVC).

It's only a matter of time before some clever manufacturer's figure out how to take advantage of that HD-SDI tap (in a small form factor) and the Canon suddenly becomes truly codec agnostic (in many ways it already is).

Interchangeable lenses. Meh.
Full raster 4:2:2 HD-SDI. Meh.
Full resolution 1080 chip. Meh.
24F, 30F, 60i. Meh.
Hundreds of accessories pre-built for it. Meh.

BUT THE HVX CAN DO 60P. WOOT!

[John Benton]

Originally Posted by Barlow Elton

https://i.cmpnet.com/dv/video/4cam-1080cams.mov.zip

I believe it's handling the weeble wobble fairly well.

Yes,
but look, you can see the lens abberation (Blue & Red borders) around the black line on the Left on the H1.

Yes, forums are love fests. And to a certain extent they should be:
ie. I LOVE My Camera.
And hey, we all want to be able to hallucinate our dream camera; especially before we get our hands on it and after we have Paid for it.
but one of the reasons I trusted this board at DVinfo, is that it seems to be quite level headed.

J - (I Love My Camera)

[Robert Sanders]

The CA of the stock Canon lens needs to be addressed by Canon.

[Steve Mullen]

Originally Posted by Barlow Elton

... every real-world shooting with an HD monitor I've done in a controlled environment showed to my human eyeballs that 24F is actually *slightly* more sensitive than 60i.

YOU ARE CORRECT. I had read early posts that claimed the opposite, but I went to the Canon site to confirm the small INCREASE in sensitivity. That lead me to alter my first post. And, we now have a puzzle.

I have no idea what then led you into a rant that has NOTHING to do with my post. And, look at the mess that followed! We are talking about the mechanism by which the H1 gets its results. We are NOT talking about the results themselves! We are NOT comparing camcorders!

Let's get back on topic.

[Barlow Elton]

Originally Posted by Robert Sanders

The CA of the stock Canon lens needs to be addressed by Canon.

No doubt. But then again, this is where Canon will be Canon. What? CA?!Fringing?! Not on our camera!! Not with OUR lenses!!

What are your settings? Oh, that's just internet forums...there's no problem.

Try calling them and you'll see. I like a lot of people at Canon USA but I hate the smug Sony-esque arrogance. If they want to keep customer goodwill they need to tell us what's really going on and if it's fixable. Again, I don't think it's show stopping but I hate denial/obfuscation of issues.

JVC seems to be doing right by their customers. At the very least, for $9K, they could tell us the good and the bad news. I fairly sure they have the ability to do firmware updates via SD cards. Let's hope the growing chorus of complaints over this anomaly will motivate them somehow.

If noise won't do it, I'm sure a financial hit will.

[Steve Mullen]

Barlow, Roberts, and John -- your posts are TOTALLY OT.

Are you guys totally unable to resist posting that you'll use any thread to carry on your debate on some topic that clearly has nothing to do with 24F?

[Barlow Elton]

Ok, Steve, fair enough. I do appreciate what you bring to the table, but you must understand that even the tone of a post like yours would almost seem to add to the FUD that seems to be swirling around. It can get a little frustrating as an H1 owner because it seems like there's always a lot of silly naysaying going on.

Thank you for the time you put into solving the riddles of these cameras.

Could it possibly be that somehow Canon actually has a progressive image to begin with?

[Chris Hurd]

Originally Posted by Barlow Elton

Could it possibly be that somehow Canon actually has a progressive image to begin with?

To begin with? No. But to end with -- practically. For all practical purposes, Frame mode is progressive scan, in that it produces the same visual results as progressive scan. As Robert points out above, how it looks is far more important than how it happens. The operator's manual for the XL H1 actually refers to Frame mode as the progressive mode. For those who remain fixated on whether or not it's "true progressive," the real question is, what difference does it make? Not much, apparently. And that's all that should really matter.