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Why EVER use interlaced?
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In short: Psf only happens in cables and tapes.
No sense when talking about a digital file.
rafael -
But the question remains: how is 30Psf different from 60i. The Wiki page simply describes an interlaced signal containing 30p. 60i does this already, what does 30Psf gain one? Does it contain metadata in the stream that would help an MPEG2 encoder, or invoke 2:2 on a display. I imagine the reason Aja doesn’t include 30Psf is there is no difference.
John Heagy
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[Rafael Amador] “n short: Psf only happens in cables and tapes.
No sense when talking about a digital file. “Precisely! This is the context that should be mentioned went speaking of 1080p and interlace.
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precisely NOT.
Interlacing in a digital file, you get the ‘artefacts’ where the OP was complaining about.And now i’m tired of this discussion, as it jumps all over the place.
Peace out,
Bouke
https://www.videotoolshed.com/
smart tools for video pros -
[gary adcock] “I am with Shane on this one.
1080 is always transported as an interlaced signal- as that is what PsF is – an interlaced transmission and distribution signal that can interpreted as either progressive or interlace depending on whether the receiver can understand progressive. “
I disagree, John is correct on this one.
1080 is not transported as an interlaced signal, unless it was originated as an interlaced signal. If a camera is shot at 23.98p, 24p 23.98psf or 24psf, the signal is progressive, not interlaced. The psf signal is transported and recorded as what could be viewed as a TDM (Time Division Multiplex) representation of the progressive signal, where half (odd lines) are read out of the frame buffer and placed into the stream during one field time, then the other half (even lines) are read from the frame buffer and placed into the transport stream during the next field time. It could have been done by reading the top half of the buffer (lines 1-540), then the bottom half (lines 541-1080) and have had the same result, but the odd/even line approach allowed an interlaced monitor to display the progressive frame without having to have an (at the time) expensive frame buffer before the CRT. It is important to understand that since all that is being done is manipulating the timing of the transport of each line, but not the information of of each line, there is no change to the original signal, so therefor it stays progressive. Interlacing would only occur if there was some difference between the two halves of the frames being applied during the transmission, which does not happen.
In the end any display will interpret the psf signal as progressive, since that is what it is. It may (if it is a CRT) display it as odd/even lines, but it is still progressive, with no temporal difference between the odd/even lines. If the signal is interlace, the display will, if it is a CRT, display it as interlace, since that is what it is. There could be a temporal difference between the odd/even lines because of this, depending on the content (still or motion). If it is a more modern display, it will most likely display it as progressive in either case, by de-interlacing and scaling to fill the display. The means and methods of that process is very dependent on the make/model of the display, so the look can vary greatly with the same content.
In the end, there is no difference between psf and “true progressive” with the exception of the transport stream. When the final signal is displayed or processed, they are identical.
Sorry to be so long winded, and maybe overly technical, but hopefully this will clear some confusion and not add more.
Glenn Kenny
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[Glenn Kenny] “In the end any display will interpret the psf signal as progressive, since that is what it is. It may (if it is a CRT) display it as odd/even lines, but it is still progressive, with no temporal difference between the odd/even lines. If the signal is interlace, the display will, if it is a CRT, display it as interlace, since that is what it is. There could be a temporal difference between the odd/even lines because of this, depending on the content (still or motion). If it is a more modern display, it will most likely display it as progressive in either case, by de-interlacing and scaling to fill the display. The means and methods of that process is very dependent on the make/model of the display, so the look can vary greatly with the same content.”
Glenn,
Thanks for your explanation. It gets into an area that I’ve often found difficult to get my head around and to collect all the facts surrounding it. I understand that PsF was developed in part to reduce the bandwidth of transmission of progressive material. By squirting out only half of the image at a time, the pipe transporting it can be smaller. If the whole frame squirts out at once, even though the total amount of data is the same in the end, that big squirt requires a fatter pipe.Another thing that seems often overlooked is that truly interlaced transmission is displayed by interlaced devices (such as a ten-year-old Sony PVM monitor) as a constant stream of interlaced fields. These devices can’t do any sort of 2:2 pulldown, frame buffering, or deinterlacing. Unless I’m mistaken, they simply display fields as they get them. The result is interlace “artifacts” in all cases. When the transmission is i59 all of the fields have a temporal difference. When the transmission is p29 (please forgive the shorthand) every third field will have a temporal difference from the one it is interlaced with. Hence, the artifacts, which are readily seen when I play p29 material through my Kona card to a CRT monitor.
– Tom -
[Tom Brooks] ” I understand that PsF was developed in part to reduce the bandwidth of transmission of progressive material. By squirting out only half of the image at a time, the pipe transporting it can be smaller. If the whole frame squirts out at once, even though the total amount of data is the same in the end, that big squirt requires a fatter pipe. “
The band with is exactly the same.
Split or not, you pass 1920×1080 pixels per second.
rafael -
[Rafael Amador] “The band with is exactly the same.
Split or not, you pass 1920×1080 pixels per second. “Correct…
Fields = little squirts
Frames = big squirtsInterlacing is a form of compression to avoid 60 frames per second. Instead it’s 30 interlaced frames per second… aka: 60i.
It preserves temporal resolution at the expense of spatial. 60lbs in a 30lb bag.John Heagy
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