Sean Oneil
Forum Replies Created
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This is bad. Thanks for discovering this problem.
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[JeremyG] “Wouldn’t the p frames just get segmented to two fields? “
Yes I would assume that is how it works. All that matters is that it maintains the full 1080 lines (or 720 lines) for every type of HD cross-conversion except when going from 720p60->1080i (in which case it loses resolution in favor of keeping the 60fps).
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[gary adcock] “I liked this question so much I asked the guys at AJA to let me know. “
Cool, but that wasn’t a question :). That was me saying I tested it out using res patterns and all is good. Nothing to worry about. The Kona 3 does in fact maintain the highest spatial quality possible during those conversions.
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[JeremyG] “1080i conversion from 1080psf and 1080p30? What did you convert to? “
To 1080i.
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I just tested a 1080i conversion from 3 sources. 720p30, 1080psf, and 1080p30. All is kosher. Nothing to worry about. It does the conversion while maintaining the full spatial quality.
Can’t post a video but here are the test patterns if you’re interested:
https://www.tigerdave.com/test_patterns.htmIt’s an overscan pattern that also works as a resolution tester (notice the alternating horizontal lines).
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[JeremyG] “720p30 will result in 1080p30.”
Yeah but how do you know it’s not down-rezzing to 540 first then line-doubling it to be 1080? There’s no way to really know without using a test pattern (which I’ll do Monday).
720p30 is the same timing signal as 720p60. It just has 30 redundant frames added to it, so each frame is displayed twice.
My point being, when converting this to 1080i, the Kona 3 quite possibly does pull 1 field per frame just like it does with 60fps 720p. “Method 1” as I’m calling it. Since there’s only 30fps to begin with, it would look no different than if it used “Method 2”. Hence your statement above. Only the resolution quality would be a little degraded – impossible to tell without a test pattern or an A/B comparison.
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Tom, we’re mostly in agreement. I never said the Kona deinterlaced anything. I said it doesn’t care because it just sees a 1080i signal. What I am saying is that the Kona’s method for converting 720p (by first scaling to 60 half frames as oppose to 30 full frames) is not some kind of industry standard. It’s just one of two ways to do it. I’ll refer to them as “Method 1” and “Method 2”.
“Method 1” is meant for to be deinterlaced using Bob and/or line doubling. “Method 2” is meant to be deinterlaced using weave or inverse telecine.
When you say this:
[Tom Brooks] “Your description, in a roundabout way, describes the shortcomings (and advantages) of all interlaced formats when compared to progressive formats of the same frame rate. Interlacing is a way of reducing the bandwidth that must be broadcast while maintaining the perception of high resolution.”
I get the impression you think all 1080i conversions are done this way. That is absolutely not true. If the source footage is not 60fps to begin with, then “Method 1” is vastly inferior to “Method 2”. You lose half the resolution yet gain nothing because the footage wasn’t 60fps to begin with. That is not good. When an HDCamSR deck has a 1080psf24 tape loaded, and it is spitting out a 1080i signal from it’s converter board, I assure you it is using “Method 2”.I am now curious how the Kona creates 1080i footage when the source is not 60fps. 720p30 or 1080psf24 for example. If it still scales these source types using “Method 1”, then that is a problem. A huge problem. In fact, not that anyone here would listen, but I would say if that is the case people should absolutely never, ever use the Kona 3 to convert 1080i from another HD source. Hopefully it’s smart enough to know better. I’ll test it Monday using a pixel test pattern.
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[JeremyG] ” This is 1080i30, not 1080p60. “
Nobody’s talking about 1080p.[JeremyG] “By your method, all 1080i is 540p60, I guess that’s not wrong, but it’s not exactly right either.
“
It’s not right or wrong. They’re just different formats within a 1080i video signal. When the Kona does the conversion it’s meant to be played at 540p60. When FCP does the conversion it’s meant to be played at 1080p30. There are two methods of deinterlacing called “Weave” and “Bob”. I suggest Googling them if you aren’t familiar with the terms.“Weave” blends fields A and B together to create thirty 1080 progressive frames. “Bob” displays each field individually as sixty 540 progressive frames. Now you’re probably thinking “TV’s don’t display 540p!”. Actually some do, but you’re right most do not. So after the “Bob” deinterlace, it will apply “line doubling” which is exactly what it sounds like.
Basically, the Kona’s conversion of 720p60 to 1080i is meant for a Bob deinterlace. The FCP’s conversion is meant for a weave deinterlace.
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[JeremyG] “Nice! That’s exactly what is expected. THis is not 540p, this is two lines of ‘540p’, which equals 1080i. “
You really don’t understand this do you. You are focussing on the wrong thing. That video can be 1080i30, it can be 540p60, it could be 320p120, it could be 2160i15. It all depends on how the playback device interprets it. That’s how digital video works. In this case the Quicktime player is interpreting it as 1080i30, and it is wrong of course (why it looks like crap). However, Final Cut, for example, WILL interpret it properly as 540p60 under certain circumstances.
The h264 encoded one I posted earlier will not work so use this one instead, it is the original capture file from the Kona conversion:
https://www.geocities.com/lifterus/test.zipPlay it in Quicktime. Same thing, right. It’s blending mismatched fields together because it is mis-interpreting this as 1080i30 when it is supposed to play back as 540p60.
Now import it into FCP and create a 60p sequence. Drag it in there and do not change sequence settings. Jog through and look at the Canvas. You’ll see 60 p frames per second. A 540p60 picture, which is how this footage is meant to be played back.
I hope you understand now. If not, I don’t know what else to say. Do you think those extra 30 frames appeared magically out of thin air?
[JeremyG] “Re: 720p59.94 to 1080i29.97”
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