Video Processors FAQ - under development - please help

[yubyub]

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

[markrubin]

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

[yubyub]

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

[Mark Rejhon]

Hi,

Here's some useful information:

Stacey Spear's DCDi Overview
http://www.dcdi-video.com/technology...-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!

[jlm]

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?

[markrubin]

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

[esandman]

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.

[yubyub]

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

-Jon

[ldturner]

Jon,
great job. very, very helpful.

[yubyub]

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

[Glimmie]

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

[yubyub]

Glimmie,

Excellent material! Thank you very much!

-Jon

[Dizzman]

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.

[yubyub]

Dizzman,

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

-Jon

[Dizzman]

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

[yubyub]

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

[duffin]

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/showt...hreadid=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 $$. :}

[yubyub]

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

[duffin]

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

[yubyub]

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

[QQQ]

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.

[yubyub]

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.

[markrubin]

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.

Jon

don't let the studios find out about this

Mark

[yubyub]

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

-Jon

[oferlaor]

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...

[yubyub]

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

[oferlaor]

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").

[yubyub]

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).

[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_books...FormatJargon10

[yubyub]

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,