With Mark Rubin's help, I've setup a web page to help coordinate FAQ questions and answers. Please visit http://www.yubyub.net/scalerfaq to take a look at the existing questions and answers. If you would like to contribute a question, an answer or a suggestion please email it to scalerfaq@mlm.yubyub.net along with any pertinant references or other helpful info.

Please note that the questions and answers will only be present in their "raw" uneditted form until such time as we begin to sort and edit them. Once it's complete, the FAQ will be handed over to AVSForum for general consumption (although I'm guessing others will maintain it).

Also, please note that any questions or answers submitted will be incorperated into the FAQ (with attribution or without - your choice), so if you suggest or answer anything, expect that it will be made public.

Thanks to everybody, especially Mark Rubin, Allan Jayne and Ofer, for their help and contributions so far.

What we need people to contribute are:

1) Questions - if you have questions that aren't answered in the FAQ, please let us know! This FAQ is designed to help people, so some of the most important input we can gather is what people need help with. Be sure to check the FAQ first to make sure your question isn't already posted.

2) Answers - if you've got answers to posted questions, let us know!

Also, note that is is a work in progress, not the FAQ as it will be posted. In a short amount of time, we will digest and edit all of the info provided into a comprehensive FAQ.

I will try to make updates to the web page as time allows. I will post the date and time I updated the FAQ (along with what changed) at http://www.yubyub.net/scalerfaq

Please keep the info coming!

-Jon

Jon- great job

to all forum members:

please feel free to post comments/questions/answers in this thread-

we will eventually post a new thread in final form to replace this one

please add your comments/expertise to any question or propose new ones

Mark

I could use some input on a few items I'd like to include in the FAQ:

1) History - what companies came about, and when? What major milestones did the company contribute to video processor development? Facts such as Deuce made the first scaler, Faroudja was the first to really tackle video deinterlacing, etc... would be most appreciated. Also, if there are any neat history tidbits, I'd appreciate it if you could drop me a note.

2) Different brands of processors available. I know about Deuce, Silicon Image, Faroudja, Key Digital, Snell & Willcox, Terranex, and Focus, but what about other companies?

3) History of PAL video. I'd like to include a European slant to the document, but I don't know much of PAL video. I need references, history, facts, etc...

Thanks for the input so far - please keep the ideas coming!

-Jon

Hi,

Here's some useful information:

Stacey Spear's DCDi Overview
http://www.dcdi-video.com/technology/articles/sage-dcdi-overview.html

Information About 3:2 by Secrets of HT & HiFi
http://members.rogers.com/tholbrook/other/pgscan.html
(You probably got this already, but this is very good.)

I also provided an algorithm plan for what I believe to be the world's first open-source implementation of the 3:2 pulldown algorith, now currently used in dScaler ( http://www.dscaler.org/Authors.htm ).

You should also give TAW, Key Digital and Immersive Inc. mentions as well for the PC based products (PC based appliance, and PCI based card.) I realize that TAW may be infamous in other ways, but the contribution was groundbreaking in that it used a standard PC architecture!

one of the functional uses of an external scaler is for switching among various signal sources. Given the recent developments re. HDCP, in which a source can only output an encrypted HD signal via DVI, the extrnal scaler would have to have multiple dvi inputs and be able to pass through the encrypted HD/DVI. Is anyone addressing this? does the new HD Leeza have multiple dvi inputs?
what if you have more than one display device...multiple DVI outs?

In the case of the pioneer plasma, apparantly the Key card will take HDCP/DVI in, but how would you switch sources? would you need BOTH the Key card and the HD Leeza?

John

good point-

an external processor with DVI-HDCP input and encryption flags turned on will ONLY output that signal through its DVI-HDCP output- and the display it is connected to must also be DVI-HDCP

ideally you want 2 or more DVI-HDCP inputs on a plug in board

Mark

I've got some more questions for the faq

a) Can I use my HTPC/HCPC instead of a scaler, and get the same sort of performance as a dedicated scaler?

b) What about the difference between displays with rectangular & square pixles, and how does the scaler compensate?

Not sure of the answers, but that's why I'm posing the questions...

A.

Good questions. I'll try to take care of them today.

-Jon

Jon,
great job. very, very helpful.

Gee, thanks - it's not even edited or organized. The editing and organization will happen over the next few days. After this weekend (if time permits), we should have a more cohesive document.

-Jon

I cut this from one of my prevoius posts. It gives a very technical description of time base correctors and how they relate to consumer devices and processors. Thought this might be good in the FAQ
Glimmie 01-16-2003

There is no such thing as a perfect bearing. There is no such thing as a perfectly balanced wheel. Therefore VTR heads and mechanical components wader and jitter. Same goes for laser disks, DVD's and even hard disk drives.

This mechanical jitter causes the timing of the recorded signal to jitter as well. In even early B&W video recorders this jitter was not an issue. When color came about, it was intolerable. The sensitive phase modulation of the chroma signal would be upset to the point where at a minimum you get the wrong color to total loss of color. This happens several times a second. So at least the chroma portion of the signal must be corrected and that's just what the consumer machines did. The correction was analog done by frequency mixing - basic AM radio technlogy. An out of phase jittery refernece signal was made from the lumanince and mixed back with the chroma. Result was the error was subtracted from the chroma and it was now stable.

But the B&W or lumanance signal still has the jitter. In the early days of consumer VTR's this was fine. As higher quality displays came into being with 3 line comb filters, this "half way" time base correction showed it's faults. Furthermore any digitizing of the video signal requires it to be totally time base corrected or broken down to RGB before being digitized. And decoding this non-coherent video has it's own set of problems. decoding is best done with coherent signals.

A TBC corrects the whole signal (both B&W Luminance and the Chroma). It works by keeping a memory buffer half full of video. The video fills the buffer in an unstable manner and the output of the buffer is controlled by a stable reference. Suppose you have a bucket with a 1 inch pipe in the bottom through a pressure regulator. The water comes into the bucket in splashes. As long as the bucket doesn't run out or overflow, you will have constant pressure water out the pipe and not lose any of the "input" water. This is exactly how a TBC works. Now to keep the memory buffer half full which is the safest operating point, the controller actually speeds up and slows down the head or disk motors to feed video into the system as needed. Even consumer VTR's with TBC's built in use this feedback principle. This is an important point as I will expalin next.

In order to keep the video centered in memory, the TBC must be able to control the VTR or disk players motor. Only professional VTR's allow this feature. So how does a consumer machine work with an external TBC? Another form of TBC is a "full frame or field" TBC. This device has the same memory but much more, a full televuision field or even two making a full frame of storage. There is so much memory versus the amount of error it can be thought of as a bottomless pit. But it's not. Sooner or later if the video is coming in slower than the stable output reference, the buffer will empty and the controller will repeat the last field or frame while it waits for the buffer to partially re-fill. Likewise if the video is entering faster than the output reference the controller will drop a frame to catch up. For general viewing and even most editing applications, this process is invisible. Most computer input cards or video processors that can accept raw VHS use this system.

The full frame system suffers another problem in that a VHS or Laser Disk has stable chroma but unstable luminance. The chroma must be un-stabalized to match the lumanince jitter. This can be done by demodulaing the choma but there is a quality hit for this step. Many processors now do this processing digitally but that too has it's artifacts.

TBC are also used in digital VTR's and even CD players. Your lowly computer hard disk has a TBC of sorts to buffer the data. But these are simpler due to the all digital signal path.

Bottom line is that an internal TBC with the source device works best. Some consumer and most prosumer VHS machines have TBC's bult in and these are the best. Same for laser diskplayers. I have an old $500 Sony LD player which has a TBC built in. DVD, OTA, and DBS are stable signals to begin with and don't require TBC's. In fact DVD and DBS produce textbook perfect NSTC signals at least in timing requirements. Video quality is another issue with DBS. The only problem remaining is Macrovision. Most Capture cards and processors, even external TBC's choke on Macrovision. Often a cheap Macrovision buster is all that is need to fix it and for the most part they don't degrade the signal. Processor manufactures can't include them outright for obvious reasons but they can offer more sophisicated back porch clamping. This is just a Macrovosion buster wearing "legal" clothes.


Last edited by Glimmie on 05-07-02 at 06:45 PM

Glimmie,

Excellent material! Thank you very much!

-Jon

Focus did not make the first scaler. In reality, the first doubler was a scaler. just to fixed rate. All the doublers triplers and Quadruplers of old were scalers, just to fixed rate.

The multi frequency scaler came about due to the fact that the Digital displays that started coming about were not programmed for and could not understand doubled or tripled. THey needed to match with the computer rates that they were programmed for. Thus the need for the "scaler" was born.

Dizzman,

IIRC I claimed Deuce made the first scaler, not Focus. Is that not correct?

-Jon

Sorry, my bad, CSI made the deuce, but my comments still stand. The Deuce is a Model by Communications Specialties Inc (CSI) (Not to be confused with the TV show)

Scalers are any device which changes the signals Frequency/Resolution

Ah! Thanks for the Deuce/CSI. I think I might have known that, but it certainly wasn't in the front of my brain...

-Jon

How about a product availabiliy section leveled from El Cheapo to state of the art. See the HDTV Hardware synopsis on STBs as an example.

http://www.avsforum.com/avs-vb/showthread.php?s=&threadid=179095

Now my question. On a budget, I want to take s-video or composite from a satellite STB and covert it to 480p component. One signal, no switching necessary. What are my options?

Of course, I want the best quality for the least $$. :}

Duffin,

I'm planning on putting in a section with quick reviews of the popular scalers and approximate prices to help people get an idea of what the equipment costs and what kind of performance to expect.

Sorry, I haven't had too much time to organize this, but I'm hoping to do so soon.

-Jon

Just a suggestion, but I'd split the sections between list of products section and a review section

I'm not sure how extensive it will be. The object of the FAQ would be to help the person learn about video processors, and introduce them to what's out there. For extensive info, they'd have to consult the forums.

-Jon

If a video scaler is used in the forest, and there is no one there to see it, does it improve the picture? Please answer ASAP as I need to purchase a new scaler by Monday.

Actually, used as you describe it, a scaler is able to actually create details which are not in the original signal. The resulting picture is fantastically detailed. The scaler can also remove edge enhancement, corrects for colorspace differences, and makes you a smackingly strong cup of coffee.

Since you're not there to see it, though, you'll never know.

-Jon

P.S. - I know, I haven't updated or touched the FAQ in ages. If anybody wants to help out, please let me know. My copious spare time has dropped to negative values in the past few months...

P.P.S. - a scaler alone in the forest will also output, on analog component, a signal which was input to it via DVI/HDCP with the copy protection turned on.

:D

Originally posted by yubyub


P.P.S. - a scaler alone in the forest will also output, on analog component, a signal which was input to it via DVI/HDCP with the copy protection turned on.

:D

Jon

don't let the studios find out about this

Mark

As long as they never visit the forests, we'll be just fine :D

-Jon

BTW,

I don't think edge enhancement in-itself is a bad thing.

The problem with edge enhancement is the overshoot problem. It's not just the edge that gets enhanced, but the areas beyond the edge (not part of the edge itself) that get lighter.

If manufacturers can improve the edge without overshooting the nearby pixels, that might actually have a somewhat positive effect on perceived sharpness without the inducing the annoyance we all feel when watching a badly enhanced picture today...

Edge enhancement is changing the source material, which I'd rather they not do, especially given the mostly rather dumb decisions made by most studios.

-Jon

BTW,

Mark R., I would say that you personally, should get a lot of the credit (+ a special place in the Video-processors "hall of fame").

David Bott pointed out to me that a number of links on the FAQ no longer work due to the recent archival of messages on AVS. I'll try to update this tonight, to keep the FAQ in at least a stand-still state (and not move backward).

I've been wondering what all those terms are for creating custom resolutions, like Vertical Synch Width, Back Porch this and that. There is a good site that describes it all, and has pictures. Maybe this would contain good material for the FAQ.

http://www.parallab.uib.no/SGI_bookshelves/SGI_Developer/books/VFC_PG/sgi_html/ch03.html#idFormatJargon10

Terry,

Groovy. I'll try to incorperate it into the FAQ. My time recently has been rather limited, but it's good to post here - I can return and collect the info when I have time.

Thanks again,

Can't read the FAQ, because of the archive problem mentioned, so I can't tell if my question is covered.

My question is:

Can you use a scaler to scale down to lower resolution? Can you receive 1080i video and convert it down to 480i for recording? (I suspect the scaler can't keep up with the 1080i input).

Related question, Is there a way to record 480p to hard disk or other medium?

Some scalers can downconvert, others can't. I don't know of a single scaler, however, that can scale down 1080i to 480i (scalers don't usually go down as low as 480i). This could be a good suggestion for Lumagen and DVDO to put into their scalers (they can both down convert).

While the links to the original questions may not work, the answers are all hosted on http://www.yubyub.net/scalerfaq/faqanswers.htm - so you should be able to read the answer if there is one.

Sorry, I just don't have the time to sit down and update the page to reference the archive. If anybody wants to update it and send me the page, I'd be happy to repost it...

For the good of the forum, the very intent of a FAQ, to educate and avoid repetitive Q's and A's, shouldn't the Q and A thread be brought from the archives and placed near the top of this forum?

1) only the origin of the questions are in the archives. All of the questions and answers are in the FAQ. I don't understand what issues people have with the origin of the questions being in the archive.

2) I don't have time. If anybody does, please go ahead and work on it. I can only host it now.

I guess imitation is a sincere form of flattery.

http://www.climaxtek.com/Faq/GeneralFAQ.htm

Right off of the FAQ we've created. In fact, it is the FAQ we've created, copied onto their site. Anybody know who the heck Climaxtek is?

Looking through the climatek website, I saw this contact info:

Steven Liao
Fountain Valley, CA 92708
(717) 964-2864

I did a search of the forum and guess what I found!!!!:eek:

Steven Liao (http://www.avsforum.com/avs-vb/member.php?s=&action=getinfo&userid=76484)

Strangely enough, this guy has only posted once, and that was over 6 months ago... And guess which forum he posted in!!! You guessed correctly, the Video Processor forum! While his forum profile says his location is Taiwan, the website also listed in his profile contains a phone number from California...

This circumstantial evidence is overwhelming. :mad:

IDK, I just think the lack of courtesy is annoying. It's free information, so I can't see a problem with them using it. But the lack of courtesy (ask first?), and contribution is annoying.

Oh well, what a world, what a world...

This is my first post but here goes...

Thought I would chime in concerning scalers. I know Teranex is currently out of range for most HT (our lowest priced box is around 17K list price currently, digital I/O only) but it will do up and down scaling. Important to remember that even our cheapest scaler uses the same algos that are in the bigger systems.

On down conversion, there is a very good chance that the DVD you see has been down converted from an HD master using a 3 or 6RU Teranex. We have variable, anamorphic, or centercut (full screen w/pan-scan) aspect choices. FYI, you can also zoom into the HD image up to 200% when down converting.

On enhancement, we use the unsharp mask filter, which in my opinion is far superior to anything else I have seen. It has a - 7.0 to + 7.0 range and works VERY well. At the '0' setting the enhancement is off. You would normally use this on ups.

At last count there were 50+ Teranex's in HT around the world, most here in the US. The HT box type varies from our large 6RU 'all you can eat' system (just a few) to the 1RU 2 channel blade that we sell. FYI the blade is running the same algo as the big box but is limited to up and down only. Same enhance and NR algos as the big guys.

Not trying to sell Teranex at all but just stating some facts about the system. Hope I didn't get to far off the subject here.


Ray

Well now we will see Silicon Optics changing the way the world see's video all for the price in upcoming OEM boxes at ZERO off the previous price . That for under $2k for entry level and prehaps included in upcoming LUMAGEN skews .

The future's so bright I got to wear shades at least they won't be perscription ones needed anymore !!

Originally posted by tstand
I've been wondering what all those terms are for creating custom resolutions, like Vertical Synch Width, Back Porch this and that. There is a good site that describes it all, and has pictures. Maybe this would contain good material for the FAQ.

http://www.parallab.uib.no/SGI_bookshelves/SGI_Developer/books/VFC_PG/sgi_html/ch03.html#idFormatJargon10

I've always wanted such a guide, but unfortunately the link no longer works. Do you or anyone else have an alternative source.

Cheers,
RAM.

Here is an idea that I did not see in the FAQ.

For those that are buying or even who own low to mid range projectors like the Panasonic AE-700 or the Sony HS51 and those that own the higher end projectors like the Sony Qualia, what can we expect a scaler like the iScan DVDO HD+ to do for us.

I know, this is something that would probably have to be maintained as new generations of projectors and processors come along, but it is a good question in my opinion. Even though it would have to be answered in a broad sense because of so many variables, it would help newcomers to this aspect of the hobby get an idea as to what one could expect a scaler/processor to do for them.

I am at a fork in the road and am desperately trying to find out this answer.

Example, you could state how a scaler/processor improved HD quality... if it all on projectors like the AE-700 and the Sony HS51 vs what a scaller does for something like a high end Qualia.
Then list any improvements in DVD picture quality... if any, then what improvements were noticed in standard definition in the same manor.
Again... I know this would require a broad answer, but it would give those of us who are unfamiliar to this portion of the hobby something to start on.


Craig :)

ive read this thread, ..... but this is so confusing. have some extreme nOOB questions: here goes...

1. scalers & processors are the same thing?
2. DVDO iscan HD is a scaler??!!! ... then which are the processors??!... faroudja DCDi ??
3. sooo... if i have a $100 dvd player (panasonic s47) and i use DVDO iScan HD , wud it give better results in video than $3000 dvd player ??... as in better black levels, good images,colors etc etc. ??

ive read this thread, ..... but this is so confusing. have some extreme nOOB questions: here goes...

1. scalers & processors are the same thing?
Yes and no.

Practically, yes. You'll see the terms used interchangably.

Technically, no.

Scaling is the process of re-scaling a video source. For example, DVD is natively 720x480 (for NTSC sources). If you converted that to 1024x768, that's scaling. Even if you converted it to 320x240 or such, it's scaling.

Processing is a more general term, and can refer to a bunch of things (deinterlacing, scaling, etc).
2. DVDO iscan HD is a scaler??!!! ... then which are the processors??!... faroudja DCDi ??
DVDO IScan HD is a processor which scales. It also deinterlaces.

Faroudja DCDi is a technology which helps with deinterlacing video sources as opposed to film sources. See the FAQ for descriptions (3:2 pull down, etc.).
3. sooo... if i have a $100 dvd player (panasonic s47) and i use DVDO iScan HD , wud it give better results in video than $3000 dvd player ??... as in better black levels, good images,colors etc etc. ??
It all depends on what the $3k player does.

Remember the old adage of "garbage in, garbage out" - a processor can't create new information - it can only reinterpret the existing video signal. So, while it can make the signal appear better, it is an illusion - there is no more information present than in the original signal.

So, the question is more one of which DVD player/processor combination produces a better video - the $3k one, or the $100 one. And it doesn't all depend on price - back in the day, there were Panasonic models which ran $300 or so which were top of the line, beating out much more expensive alternatives.

Hope this helps,

05.07.13
With my svhs wearing out, and stores kinda geting out of the vhs market, one has to move towards dvd and hd recording of tv programs (esp time shifting so one can review programs at a later date.)
But:
1. It seems the fcc is going to broadcast flags that stop recording content, and recorcing audio seems to have be done through analog channels.
2. geographic restrictions mean dvd from other countries/ areas are not playable.
3. Some recorded content has a timer, where it is unscramblable /viewable after a set amount of time.
So:
Interested in opinions especially as the fcc mandates hdtv by 2007, if one wants to update their home AV system and still review vhs tape archive or update to dvd or dual layer dvd while still time-shifting their tv and hdtv programs, what recording media or recorder should one consider. It is hard to even find svhs tapes anymore or replace heads worn out from usage. So recording to the 250 and 500GB hd seems the future. And converting older computers to a personal storage-burner may be what is needed.

But,

Get one of the combination hard drive recorder/ DVD burner something like a Panasonic T3040.

You can transfer your VHS tapes onto DVD and time shift your standard def programming onto the hard drive. Some, not HD receivers allow you to get a svideo signal that could be routed into the player.

yubyub thanks for the reply! :) it really helped and i read the FAQ page, very well laid, it answered to a lot of my questions. ... BUT it raised another question in my mind.here goes.

1.it all comes down to the source. the current dvds are in 480i format. would it be possible to have 480p or 720p or 1080i or 1080p formats on the upcoming HD-DVD or blu-ray discs?
2. if it is possible to do that then would'nt it not require the job of a scaler? and a connection frm a decent player to the display would be enough ???

yubyub thanks for the reply! :) it really helped and i read the FAQ page, very well laid, it answered to a lot of my questions. ... BUT it raised another question in my mind.here goes.

1.it all comes down to the source. the current dvds are in 480i format. would it be possible to have 480p or 720p or 1080i or 1080p formats on the upcoming HD-DVD or blu-ray discs?
That's the hope. I believe current Blue-ray stuff is at 1080i, but I haven't been following it closely. It should be above 480p.
2. if it is possible to do that then would'nt it not require the job of a scaler? and a connection frm a decent player to the display would be enough ???
Not unless your display could show 1080i and/or 720p natively. Currently, the only devices which do that are analog projectors, i.e. CRTs and such.

Since digital projectors have a fixed panel size (i.e. 1280x720), a scaler is still necessary to scale from 1080i (which is 1920x1080 interlaced) to 720p (which is 1280x720). Note that, in this case, 720p would map directly onto a 1280x720 display - which is one of the reasons modern DLPs are created in exactly that resolution.

05.07.13
With my svhs wearing out, and stores kinda geting out of the vhs market, one has to move towards dvd and hd recording of tv programs (esp time shifting so one can review programs at a later date.)
But:
1. It seems the fcc is going to broadcast flags that stop recording content, and recorcing audio seems to have be done through analog channels.
2. geographic restrictions mean dvd from other countries/ areas are not playable.
3. Some recorded content has a timer, where it is unscramblable /viewable after a set amount of time.
So:
Interested in opinions especially as the fcc mandates hdtv by 2007, if one wants to update their home AV system and still review vhs tape archive or update to dvd or dual layer dvd while still time-shifting their tv and hdtv programs, what recording media or recorder should one consider. It is hard to even find svhs tapes anymore or replace heads worn out from usage. So recording to the 250 and 500GB hd seems the future. And converting older computers to a personal storage-burner may be what is needed.
Bug,

I'm not sure what any of your comment has to do with a Video processor and scaler FAQ. Please post in the appropriate thread (indeed, in the appropriate forum as well) in the future.

no hot yes

no hot yes
The mind reels...

I hope i don't sound dumb
I am getting a sceptre 42''lcd and was looking to find out who made the chip in it?
The sceptre is supose to up scale to 1080p ?how does this work?

Hi,

May adventures in video scaling started with Immersive Technologies introduction of the HOLO3D computer based PCI scaling card ( now out of production).

I was one of the Beta testers which afforded me access and preferential pricing on the HOLO3D and an SDI modified Panny rp82 dvd player.

For those not familiar with this video scaling card, Tom Strade it's inventor and Mark Rehon who wrote the code for it ingeneously used the computers operating system and onboard vid card (combined with EntechTaiwan's Powerstrip and even D'Scaler for the more sophisticated of us) to do all of the work that a store bought black box video scaler did back in 2002 for 1/3 of the price.

It only worked with a 408i signal from outboard equipment. Cable/sat/vcr/dvd and such. It would then scale the 480i to any resolution that your display could handle. It had SDI, Composite, Component and S/Vid inputs.

At that time 1080i was the cats ass. 1080p is NOW beginning to get some notice.

My question is do you think that the DCDI chip on this card (2002 vintage) combined with today's much more powerful PC VID cards could scale a signal to a display which accepts 1080p? If not why?

Or do you think it is possible to just switch out the DCDI chip on the PCI card to a 2006 model without a whole new set of code having to be written?

Thanks,
Peter M.

I am thinking of buying the JVC RS1 but the dam thing will not stretch for my anamorphic lens and CIH system. The JVC has a Genum chip which does its internal video processing so how does an external processor override the internal processing.

Say two years from now HDMI 1.3 becomes the video standard by changing to an external processor can I uprade without changing the projector. Also can an external processor change the standard output frequency to 24 frames a second

First off, my compliments to the already fine FAQ. Here are my two related questions:

1) Can I store the output of a scaler on a hard disk or can I burn the output to a DVD? The purpose would be to use the improved image on another system - which would not have the scaler.

2) What would happen if I fed the output signal back into the scaler? Would the image improve, degrade, or remain the same?

You can store the output of a scaler on a hard drive if the storage system accepts that format of video (e.g. 480p).

It is not practical to burn scaler output on regular DVD's because the DVD storage format is 480i.

Generally, recording the video after it has gone through a scaler and playing it back through another scaler will result in a worse image compared to one de-interlacing move if needed followed by one scaling that went all the way to the desired resolution. Now, there is no inherent problem with going from 480i to 480p in one place and going from 480p to 720p in a different place since these are the de-interlacing and scaling steps that are a distinct step 1 and step 2.

Video hints: http://members.aol.com/ajaynejr/video.htm

I cut this from one of my prevoius posts. It gives a very technical description of time base correctors and how they relate to consumer devices and processors. Thought this might be good in the FAQ
Glimmie 01-16-2003

There is no such thing as a perfect bearing. There is no such thing as a perfectly balanced wheel. Therefore VTR heads and mechanical components wader and jitter. Same goes for laser disks, DVD's and even hard disk drives.

This mechanical jitter causes the timing of the recorded signal to jitter as well. In even early B&W video recorders this jitter was not an issue. When color came about, it was intolerable. The sensitive phase modulation of the chroma signal would be upset to the point where at a minimum you get the wrong color to total loss of color. This happens several times a second. So at least the chroma portion of the signal must be corrected and that's just what the consumer machines did. The correction was analog done by frequency mixing - basic AM radio technlogy. An out of phase jittery refernece signal was made from the lumanince and mixed back with the chroma. Result was the error was subtracted from the chroma and it was now stable.

But the B&W or lumanance signal still has the jitter. In the early days of consumer VTR's this was fine. As higher quality displays came into being with 3 line comb filters, this "half way" time base correction showed it's faults. Furthermore any digitizing of the video signal requires it to be totally time base corrected or broken down to RGB before being digitized. And decoding this non-coherent video has it's own set of problems. decoding is best done with coherent signals.

A TBC corrects the whole signal (both B&W Luminance and the Chroma). It works by keeping a memory buffer half full of video. The video fills the buffer in an unstable manner and the output of the buffer is controlled by a stable reference. Suppose you have a bucket with a 1 inch pipe in the bottom through a pressure regulator. The water comes into the bucket in splashes. As long as the bucket doesn't run out or overflow, you will have constant pressure water out the pipe and not lose any of the "input" water. This is exactly how a TBC works. Now to keep the memory buffer half full which is the safest operating point, the controller actually speeds up and slows down the head or disk motors to feed video into the system as needed. Even consumer VTR's with TBC's built in use this feedback principle. This is an important point as I will expalin next.

In order to keep the video centered in memory, the TBC must be able to control the VTR or disk players motor. Only professional VTR's allow this feature. So how does a consumer machine work with an external TBC? Another form of TBC is a "full frame or field" TBC. This device has the same memory but much more, a full televuision field or even two making a full frame of storage. There is so much memory versus the amount of error it can be thought of as a bottomless pit. But it's not. Sooner or later if the video is coming in slower than the stable output reference, the buffer will empty and the controller will repeat the last field or frame while it waits for the buffer to partially re-fill. Likewise if the video is entering faster than the output reference the controller will drop a frame to catch up. For general viewing and even most editing applications, this process is invisible. Most computer input cards or video processors that can accept raw VHS use this system.

The full frame system suffers another problem in that a VHS or Laser Disk has stable chroma but unstable luminance. The chroma must be un-stabalized to match the lumanince jitter. This can be done by demodulaing the choma but there is a quality hit for this step. Many processors now do this processing digitally but that too has it's artifacts.

TBC are also used in digital VTR's and even CD players. Your lowly computer hard disk has a TBC of sorts to buffer the data. But these are simpler due to the all digital signal path.

Bottom line is that an internal TBC with the source device works best. Some consumer and most prosumer VHS machines have TBC's bult in and these are the best. Same for laser diskplayers. I have an old $500 Sony LD player which has a TBC built in. DVD, OTA, and DBS are stable signals to begin with and don't require TBC's. In fact DVD and DBS produce textbook perfect NSTC signals at least in timing requirements. Video quality is another issue with DBS. The only problem remaining is Macrovision. Most Capture cards and processors, even external TBC's choke on Macrovision. Often a cheap Macrovision buster is all that is need to fix it and for the most part they don't degrade the signal. Processor manufactures can't include them outright for obvious reasons but they can offer more sophisicated back porch clamping. This is just a Macrovosion buster wearing "legal" clothes.


Last edited by Glimmie on 05-07-02 at 06:45 PM
Thank You very much for this post it was most informative.
I would like to know more about how the different formats and files work and why they exist. I'm trying to convert old VHS home movies to a Digital Format that will produce the best quality viewable NTSC DVD's.

BTW,

I don't think edge enhancement in-itself is a bad thing.

The problem with edge enhancement is the overshoot problem. It's not just the edge that gets enhanced, but the areas beyond the edge (not part of the edge itself) that get lighter.

If manufacturers can improve the edge without overshooting the nearby pixels, that might actually have a somewhat positive effect on perceived sharpness without the inducing the annoyance we all feel when watching a badly enhanced picture today...