Da vhs a digitale: settaggio acquisizione

[Andala]

Originariamente inviato da [KabOOm]
...no direi che non fa una piega, resta da verificare se conviene fare l'interpolazione in acquisizione con il formato DV oppure in compressione mpeg per metterlo su DVD...

....ora non posso controllare ma mi pare che eista anche un formato low-quality standard per DVD proprio a meta' risoluzione... possibile?

Il formato DVD accetta file video Mpeg1 con definizione 320*280 associati ad audio Mpeg1Layer2 48Khz,AC3 e DTS.

[[KabOOm]]

Originariamente inviato da Andala
Il formato DVD accetta file video Mpeg1 con definizione 320*280 associati ad audio Mpeg1Layer2 48Khz,AC3 e DTS.

..grassie

[xs 400]

Originariamente inviato da Andala
Il formato DVD accetta file video Mpeg1 con definizione 320*280 associati ad audio Mpeg1Layer2 48Khz,AC3 e DTS.

Il Mpeg1 non è quello dei videocd?

[Andala]

Originariamente inviato da xs 400
Bit rate variabile? Struttura del gop? Filtri?

Pensavo di essere meno ignorante di quel che sono!!!


Puoi dirmi qualcosa in più o indicarmi delle fonti per colmare le mie (enormi) lacune?
Ho i miei ultimi 20 anni di filmini VHS e 8mm da trasferire su DVD...
Grazie!

Sulla struttura del GOP e molto altro puoi trovare tutte le guide desiderabili su VCDHelp.

In Italiano c'è l'ottimo sito del buon Paolo Paoric www.videomakers.net . E' in italiano e trovi recensioni varie sui codec, spiegazioni sui filtri ed altro.

Buona lettura

[Andala]

Originariamente inviato da xs 400
Il Mpeg1 non è quello dei videocd?

Sì!

[xs 400]

Originariamente inviato da Andala
Sulla struttura del GOP e molto altro puoi trovare tutte le guide desiderabili su VCDHelp.

In Italiano c'è l'ottimo sito del buon Paolo Paoric www.videomakers.net . E' in italiano e trovi recensioni varie sui codec, spiegazioni sui filtri ed altro.

Buona lettura

Grazie per la disponibilità!
A buon rendere...

[Alex_e_Basta]

Sulla "risoluzione" del VHS vi segnalo questo

10.) Why is a high resolution recommended when capturing VHS.?

- We all know that VHS VCR has a resolution of 320x240?
A: First, VHS has no "resolution" of 320x240 . This is just an old rumor. Second, if you use filters, there is a big difference in using a low resolution (less informations for the filter) and full PAL (or NTSC) resolution. Last but not least it all depends on your taste, if you are satisfied with a 352x288 direct Divx ;-) capture, then by all means use such a low resolution. In the end only you can tell if the quality is satisfactory.

A very good thread that explains in theory why all those '320x240 stories' are just incorrect http://forum.doom9.org/showthread.php?s=&threadid=34122 .

[xs 400]

Originariamente inviato da Alex_e_Basta
Sulla "risoluzione" del VHS vi segnalo questo

10.) Why is a high resolution recommended when capturing VHS.?

- We all know that VHS VCR has a resolution of 320x240?
A: First, VHS has no "resolution" of 320x240 . This is just an old rumor. Second, if you use filters, there is a big difference in using a low resolution (less informations for the filter) and full PAL (or NTSC) resolution. Last but not least it all depends on your taste, if you are satisfied with a 352x288 direct Divx ;-) capture, then by all means use such a low resolution. In the end only you can tell if the quality is satisfactory.

A very good thread that explains in theory why all those '320x240 stories' are just incorrect http://forum.doom9.org/showthread.php?s=&threadid=34122 .

Qual è la fonte di questa informazione?
Si afferma che la risoluzione non è 320*240 ma non si dice quale sia quella esatta...

[xs 400]

Originariamente inviato da Alex_e_Basta
... Second, if you use filters, there is a big difference in using a low resolution (less informations for the filter) and full PAL (or NTSC) resolution. ...

Questo è teoricamente vero, ma se la full PAL resolution è ottenuta grazie all'interpolazione i filtri interverranno su un frame già molto manipolato introducendo ulteriori distorsioni del segnale...
A dire il vero non mi convince molto, ma stasera consulterò il thread indicato.

Grazie, comunque, dell'indicazione.

[Andala]

Ho letto il post sul thread di Doom9.org e ci sono non pochi errori.

Certo la risoluzione Pal è 720*576, ma si tratta in pratica di un "traguardo" da raggiungere e che si è raggiunto con gli anni altrimenti avremmo dovuto avere la definizione dei DVD già vent'anni e passa fà.

Il VHS è a risoluzione di 320*240 e li si ferma per una quastione prettamente strutturale del nastro VHS che in analogico non può andare oltre come capacità dati.
Un tale supporto ci è andato bene per anni solo perchè le TV erano ferme a quala definizione, mentre ora le cose sono ben diverse.

Inoltre se il VHS fosse stata a 720*576 che necessità c'era del SVhs con le sue 410 linee e del LD con le 440 linee?

Agli inizi degli anni novanta c'era chi s'era inventato un sistema per fare backup usando i Vcr e la massima capienza di un nastro da 240, se non ricordo male, era all'incirca sui 270 MB.


Dopo tutto se anche i tecnici sui manuali riportano per il VHS una risoluzione 320*240 sui manuali ....

[Alex_e_Basta]

Dopo tutto se anche i tecnici sui manuali riportano per il VHS una risoluzione 320*240 sui manuali ....

Il VHS , essendo un supporto analogico, NON HA, per definizione, una risoluzione, ma solo un numero di linee. Ti posto un ottimo intervento di Xesdeeni su Doom9 al thread linkato. E' un pò lunghetto, ma chiarisce molte cose.

========================================
It's so frustrating to constantly see the "VHS is 352x240" statement over and over. It's simply not true, in either dimension....

[All of these numbers apply to NTSC. Scale appropriately for PAL.]

VERTICAL
Vertically, VHS captures two fields, just like the television signal that it records. For NTSC, that's a total of 525 lines, about 486 of which contain actual video. If you record onto a VHS VCR such that the even fields are all white and the odd fields are all black, you will indeed see a horrible flashing/flickering. If 240 lines were all there were, both fields would be merged together and the results would be a solid gray. There are indeed 480 separate lines...period.

However, it does not follow that the resolution of television (any format) is 480 analog lines of (vertical) resolution: It should be obvious that the example above (even field white, odd field black) would display 480 horizontal lines. This represents the case where the lines are exactly in phase with the sensor's scan lines. But, if we shift the "lines" above down by 1/2 a line, then what will we see? In the real world, it is almost guaranteed that our sensor will see part of a white line and part of a black line, so it will have to output a medium gray. Since every scan line could see the same black/white pair of lines, the whole image would be gray. And of course this means we cannot display 480 lines of (vertical) resolution at that position.

You can follow through the logic that if we reduce the line count a bit (say 478 lines), the lines will no longer be in phase with the sensor's lines. Some will line up close enough to show distinct black and white lines, while others will degrade to gray. The question then becomes, at what point can we see all the lines at all phase relationships.

The Extended Kell Factor attempts to estimate how many lines we can actually represent with a given discrete representations (in this case scanlines). It is a range of values, not because it is a subjective factor (reading a lines-of-resolution chart is no more subjective than any reading of an analog scale, like reading a ruler or thermometer), but because of the variation between the devices that capture the video. The lens can blur the image. The sensor can have overlapping sensitivity between lines, or it can have gaps between lines. The video can be encoded or processed in any number of ways. All of these (and many other factors) will affect the ability to display distinct lines.

So the Extended Kell Factor provides a rule-of-thumb for estimating what can be displayed. Vertically, this is about 370 lines of (vertical) resolution.

However, since the lines are distinct, separate units, just like the digital lines to which they would be converted, the number of digital lines is the same as the actual number of lines (480), not the lines of (vertical) resolution.

HORIZONTAL
Horizontally, is a bit more sticky. While analog video has the distinct horizontal scan lines to limit the vertical resolution, it has no such limits horizontally. There, it is limited by analog bandwidth. Theoretically, the maximum bandwidth of a video signal will provide us with the lines of (horizontal) resolution. For (NTSC) VHS, the bandwidth is about 3.2MHz. When we divide this by the number of frames per second (29.97) and by the number of lines per frame (525), we arrive at the number of cycles per line of video (~203). About 20% of each line is used for synchronization information, so only the remaining 80%, or about 162 cycles contain image. This represents about 325 pairs of black/white lines per line.

However, lines of (horizontal) resolution is defined based on a square screen (called a "screen height"). So our 4:3 television has to remove its aspect ratio, so we get (325 * 3/4) or about 244 lines of (horizontal) resolution. This is the oft-misquoted 240 lines of resolution, that seems to be at the root of the confusion regarding VHS resolution. Note well that this is the lines of HORIZONTAL resolution, or the number of vertical lines that can be represented across a (screen height) scan line, not the number of horizontal scan lines.

When converting from lines of (horizontal) resolution to a digital representation, we need to consider the above effects once again. That is, we could use 325 pixels per VHS line, but if the (vertical) lines were not in phase with our pixels, we would lose that detail, even though the VHS signal would have no problem providing such an image. So once again, the Extended Kell Factor helps us estimate what we would need to use to have enough digital pixels so we can always "handle what VHS can dish out." 325 lines of (horizontal) resolution could be represented by approximately 423 pixels.

CONCLUSION
So from this lengthy discussion, it should be clear that VHS compares more reasonably to a digital resolution of 423x480, while 352x240 is flat wrong.

DVD "LINES OF RESOLUTION"
Also, consider one other interesting pieces of misinformation. DVDs use a 720 pixel wide line, and are often quoted as having 500 (or even 540) lines of (horizontal) resolution. Yet, according to the Extended Kell Factor, 720 pixels can only represent about 553 lines of (horizontal) resolution. When you then compensate for the "screen height" requirement of the "lines of resolution" definition, you get only about 415 lines of (horizontal) resolution. And the above discussion of lines of (vertical) resolution also applies here.

[Andala]

Ma qui mi sorge la spontanea domanda.
Va bene si afferma che la risoluzione del VHS è di 423*480(NTSC), ma allora come la mettiamo con il SVHS che ha 410 linee e il LD con 440?

Certo si afferma che il la risoluzione del DVD è verosimilmente di 500-540 linee , ma solo in presenza delle bande nere.