IRE settings

Leoslocks · Part Time Joined: 07 May 2003 Location: United States

// Alright, we'll just make this thread the sticky. It's probably as publish-ready as it'll ever be. -- moderator lordsmurf

Lordsmurf wrote: (as originally posted in this thread)

Well, this post may not be 100% perfect scientific way to explain all this, but given the alternate, images really would help. Lots of jibber-jabber and jargon only goes so far. I'm simply amazed at how confounding video information has to be. What should be basic principles of video (think "atoms have protons, electrons and neutrons") seemingly require advanced degrees in video theory. Uggh. Anyway, here goes an attempt to convey knowledge to the layman....

- DVD MPEG is IRE 0.0
- IRE is the name of the group that set the standard
- 0.0 is the "total black" side of the scale. It goes to "total white" at 100.0.
- North America (will call it "USA" for purpose of this article) has black set at 7.5 and not 0.0. Blame lazy engineers from a long time ago. Because of this, all of our equipment is different from Japanese stuff. Or at least is SUPPOSED to be different.
- When a NTSC USA player gets a DVD, it's output is stepped up +7.5 IRE so the tv understands it and it looks correct. When an analog signal (VHS, cable, tv, etc) is inputted into a digital device, the device steps down the IRE by -7.5 so it is at proper 0.0 for digital needs (playback, capture, encode, etc).

NOTE! Because IRE shares a relationship with 0-255/16-235 YUV scale, I have mushed them together for the purpose of this conversation, even though they are not "the same thing" necessarily.

Master scale for reference:

Proper DVD recorder and playback activity for NTSC USA:

Wrong IRE input, creates bad output for NTSC USA:

Wrong IRE input, but will look OK on the record (ONLY!):

This is an example of how Panasonic has NOT AT ALL addressed the IRE error, but rather shifted the luminance ("brightness" spectrum, which in turn holds mostly green color in NTSC USA):

++++++++++++++++++++++++++++++++

Some references:
http://www.thx.com/mod/techlib/contrast.html
http://www.signvideo.com/dv-black-levels-dvd-authoring-mpeg-2-part-1.htm

Related videohelp topics:
http://www.videohelp.com/forum/viewtopic.php?t=163667
http://www.videohelp.com/forum/archive/t219752.html
http://www.videohelp.com/forum/viewtopic.php?t=258753&postday ... p;start=30

Other sites/forums with related info:
http://www.avsforum.com/avs-vb/showthread.php?s=&threadid=416292
http://www.smr-archive.com/forum_6/messages/438.shtml
http://ultimateavmag.com/dvdplayers/904ayre/

++++++++++++++++++++++++++++++++

On a related note, in TMPGENC, that stupid "OUTPUT YUV DATA ..." settings is quite easy to understand (or at least IN THEORY should be). It was specifically made for DV input, but applies to anything with the wrong set of values.

OUTPUT YUV DATA ... CHECKED
>>>> LEAVE AS 0.0 IRE
>>>> FOR DV SOURCES AND DIGITAL 0-255 SOURCES

OUTPUT YUV DATA ... NOT CHECKED
>>>> CONVERT FROM 7.5 DOWN TO 0.0 IRE
>>>> FOR TRADITIONAL ANALOG SOURCES 16-235

.... then again, it DOES say 8-235 .... and I've been re-encoding MPEG files from capture cards for a long time with it .... and leaving it UNCHECKED did not in any way adversely affect the file .... so much for theory applying here .. then again, we already know that software is screwy, as is the setting data...

I'll have to come back to the TMPG stuff, not quite right yet.

And the RGB interface (not YUV) may have something to do with it .... at least the DVD recorder part of this conversation is correct (and "easy" by comparison!)

++++++++++++++++++++++++++++++++

None of this is really "final publish" quality, I'm still trying to catch mistakes, iron out any bugs, and make sure this is really the best way to VISUALLY explain this entire mess. So while helpful feedback is fine, derogatory feedback is not (and I prefer it be PM'd anyway, not clutter this thread).

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BJ_M · Patron Joined: 30 Jul 2002 Location: Canada

some dv is 0 and some is 7.5
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lordsmurf · Posted: Feb 21, 2005 16:16

I'm about to write a sticky for this topic in the DVD recorder forum. There is some more that needs to be added/re-worded first.

Patience.

Good stuff is on the way.
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edDV · Posted: Feb 21, 2005 17:15

Getting close but not quite,

All CCIR-601 derived digital video including DV, SDI, DVD, etc. have black defined as 16 and white defined as 235 for 8bits (64-940 for 10bit formats like Digital Betacam)

So in your first drawing above, the Blue line should read.
"IRE 0.0, PURE BLACK 0(ANALOG), 16(DIGITAL)"

Setup should exist only on the analog NTSC (composite and S-Video) outputs (not on component out). Setup gets added for broadcast equipment. Consumer and most prosumer equipment incorrectly output with no setup on NTSC composite. Most home theater equipment will correctly have no setup on the component analog Y out (e.g. DVD players and set top boxes).

On the input side, broadcast equipment is supposed map 7.5 IRE to level 16 digital and 100IRE white to level 235.

Consumer capture cards vary on how they handle this with most doing it wrong without manual intervention with the setups.

lordsmurf · Posted: Feb 21, 2005 17:18

Yeah, the re-mapping of black thing is the complex part. I may just have to make some sort of notation about this, and hope nobody gets confused. Probably put a carefully worded warning for newbies that are trying to learn too much too fast.

I may just say "16 remapped" or something for the 7.5 IRE.
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edDV · Posted: Feb 21, 2005 17:24

The good thing, if I/O levels are handled correctly, CCIR derived digital video is 16-235 anywhere in the world.

Let everyone catch up with this before introducing RGB remapping (0-255 to 16-235) and the gamma screwups (e.g. Final Cut Pro).

Also, on the first graph, the 255 level isn't really "PURE WHITE", 235 is. The area between 235 and 255 is there to handle transient overshoots and to provide some safety margin for out of spec white levels. If this safety zone wasn't there, any overshoot would cause serious clipping errors.

The area from 0-16 prevents clipping at the black level during transmission but is also used in a controlled studio environment to provide a below black clip level for keying graphics (sort of a poor man's alpha). These below black uses are removed before the final program gets out of the studio.

gshelley61 · Frequent Flyer Joined: 19 May 2004 Location: USA

Thanks for the clarification, edDV. Your professional perspective is definitely appreciated here.

I have tried to explain very carefully several times why 7.5 IRE black level NTSC sources must be adjusted to 0 IRE prior to DVD transfer, but it can be confusing and even folks who have been around the forum for a while may not quite understand the issue completely. As a video hobbyist, I have observed that different capturing devices deal with source black levels in different ways... which makes it even more confusing because it is impossible to suggest one method (or setting) that will work on every piece of equipment. This is one of the main reasons I use a high quality proc amp with an accurate luma/black level meter in my signal chain.

edDV · Posted: Feb 21, 2005 17:44

The addition of waveform monitors to Premier, Vegas, FCP, and AVID will help much for setting black and white levels correctly for NTSC inputs. Hopefully, these will get built into capture programs and encoders as well.

A great reference on all this is Adam Wilt's DV-FAQ http://www.adamwilt.com/DV-FAQ-tech.html

Marvingj · Posted: Feb 21, 2005 18:57

0 IRE FOR DIGITAL & 7.5 FOR ANALOG.....HEHEHEHE!!!!

zorankarapancev · Member Joined: 30 Sep 2003

Harpmaker · Member Joined: 11 May 2004 Location: Northeast USA

lordsmurf · Posted: Feb 21, 2005 21:25

vhelp · ..Semi Neutral.. Joined: 31 Mar 2001 Location: New York

Evening guys

As for the Pioneer 220S unit, I've seen good results from NightWings posting
on this unit. I liked the results so far. And, I like that image he posted
(dark scene) but I don't know what DVD movie that was from

I also want to see a head-to-head w/ the JVC DR-M10 unit vs. Pioneer 220S.

--> Lite-On DVD Recorder Model: 5101 at Sams for $139 any good?

Excuse me for buttin in here. I've had my share this issue, and then some.

There is a missing piece to this puzzle. Yes. But first, we (and I) need
to know something. And this makes sense to me, in my head. Now, I have to
place it her in writing, for you all to digest and depick with your comments
and theories (just like I have) ...

The problem is, we need to know weather or not, the source is at fault, or
the hardware, or both. We need to first determine this, and get it straight.

But..

.. I've often (and always) wondered why commerical dvd movies look so rich
.. and vibrant in color, and I always couldn't put my hand on it. I blaimed it
.. on a theory (which doesn't seem to hold up) on a color space YV12. But, then
.. further questions were ask inside my head. Color space. DVD is YUV 4:2:0
.. and YV12 is just a subset of YUV, just as YVU-9 is (spelling) they're all a
.. subset of YUV, which is broken down into an 8x8x8 color matrix, or 24bit bumped
.. down to 16bit or 8x4x4 (16bit) color space, which is then processed futher
.. through various other color/chrom/luma minipulations, etc. Anyways.
.. If this YV12 is on commercial DVD's (and is assumed a standard for DVD format)
.. then why are there any Encoders out there (ie, CCe; TMPG; MC; Procoder, etc)
.. with a swith or option or whatever, to encode with YV12, so that we could get
.. this Vibrant and Richness in color output in our MPEG-2 encodes. And, to add
.. another blow, of all encoders, CCE (and its heavy price tag) does not have this
.. feature ?? And, then final answer came to me. You got it. It's not YV12.
.. It's 4:2:0 but the missing piece still eludes me and you all. Or, perhaps it
.. has something to do with the way video is being minipulated and finalized through
.. the devices output channel. IRE. But, there lies another question (or two) Anyways.

No matter what the IRE channel is on any front (device etc) we also need to
know weather or not the final capture and/or encode to, is permanent, w/ respect
to IRE. For instance. If I capture from my DVD, and it is outputing an IRE 7.5
level, then THAT is what is being captured; recorded; or encoded to a final
source based on that level (assuming you can't alter the IRE produced source at
any juncture) and so.. If the IRE is 7.5 on my source (ie, dvd recorder's mpeg-2
or captured source, (though now my head is spinning because of the complications
that arrises from the codec and the color space and other attributes, when left
in the hands of casual/newbie users - oh well)) ..again, the final source is
IRE 7.5 now, on the source file in question. If the source is, shall I say,
"burned" or permanant on the source, say it be an AVI capture, then that means
that our capture (w/ its other attributes of codecs and color space) is a capture
of IRE 7.5 level. If we proceed to alter this with minipulations (ie, TMPGeng's
YUV filter) are we really bumping it back to wehre it should be, or are we just
"filtering" it to some other level of blackness. That is the question. My belief
is that once we capture it, then there is nothing we can do about it now.
.
If I capture something that is say IRE 7.5 level, and that is *suppose* to be
that level, then I should be encoding it at that *same* level. At least that is
what I beleive it should be. But tests need to be made (see below) in order to
know for sure. Anyways.
.
My understanding is this. If I capture something that is IRE 7.5 that is the
level of output richness I'm expecting to obtain when I view this source. However,
when things get dumped onto a pc screen, there is yet another issue with the color
space and IRE level and Vibrant and Richness in colors we see from this capture.
Things are beginning to get really confusing here. And this is why some are
starting to ask questions now. Anyways. As I was saying. things are beginning to
get messy here. Is IRE values getting re-IRE 'ed again, or un-IRE 'ed in all these
video transferences ?? And if so, How can one gain *control* of this before things
truely get messed up - like today. Things are just too messy and out of control.

About a month ago, I shared in a test scenario, where I recorded my DVD movie,
"The FIfth Element" onto a VHS tape. From my perspective, when played (VHS) on
my tv set, the movie looked pretty good, and colors *seemed* to match closely
to the dvd if I didn't count the dots, etc. But, afterward, when I proceeded to
capture this VHS tape I just recorded from DVD from, things got really ugly. I
could not match the same level of color space or output quality as that of the
DVD, let alone, the VHS tape. I don't know exactly what happended in between
the steps, but even I got lost in the shuffle of things - transferences of video
sources from one item to the other and back and forth, and so on and so forth

.
BUT, lets say, they are airing "The Fifth Element" on cable tv, and I capture it,
(just as I did with the VHS tape) and I process it.., guess what ?? Things look
just like the source Cable that aired my capture.
.
Something (and element) is surely missing. And, it aint "the fifth element"

So. If we are cerious in this endeavor, to finaly reveal the trueth to this
missing element (could be anything) then we need to setup a standard set of
tests, and a number of us should perform this test.
.
A certian test scenario or platform should be devised. One that we all can
share in and do.
.
Our setup should be consistant, and equipment should be the same. Only time
different, is when we're testing which *brand* is at fault with certain quality
attributes. ie, Pioneer vs. Panna. vs. iLO vs. Emerson, etc.

I would like to start a test, and have others join in if they can.
Using the following setup/equipment:

* Source: commerical DVD movie (matrix / 5th element / etc)
* Scenes: decide on several scenes to standardize (for the test disk, maybe)
.
* DVD player: Apex AD-1500 (region and MV hacked free)
* LD players: Pioneer CLD-V2600 / CLD-D701
.
* capture devices: advc-100 / trv22 / DVDR04 dvd recorder /
.
* Software Editor: vdub (nothing fancy here)
* Pic format: PNG

Perhaps a test disk could be made and a part of the new standard here, and
we could D/L the VOB file. If we create a standardized test disk, then that
will rule out any inconsistance w/ source. At least thats a start.
.
For an idea, here is a good example of a test scenario of making a test disk.

--> Panasonic E55 video recording test

Then, you could upload your results here. I (or someone) could tally the results
into a database, for a record, and to add bruse to this forum, we could add this
into the "dvd recorder" section, it's IRE values.

I don't know. I had much more to say, but my head is hurting, and I didn't get
a chance to do my other fun test and projects and things.

-vhelp 3140

vhelp · ..Semi Neutral.. Joined: 31 Mar 2001 Location: New York

Lets create a check list, shall we.

A - [TRUE/False] - IRE is a device-only thing. Not software filter.

B - [TRUE/False] - Commercial DVD movies that we buy are encoded MPEG-2 and
.................... @ 4:2:0 (not 4:2:2)
B - [TRUE/False] - but, if they are actually 4:2:2 then that might explain the
.................... missing element, because of the Vibrant and Richness in
.................... color quality we see when we view them on TV or rip them to
.................... our desktop pc harddrives. If this is TRUE, then we need a
.................... test app that can open a ripped VOB from a commercial dvd
.................... movie, and examine the video for 4:2:0 or 4:2:0 color space

C - [TRUE/False] - Commercial DVD movies are sub color space YV12.

D - [TRUE/False] - Most DVD player output an IRE 7.5 (NTSC) (lets assume all do,
.................... for now)

E - [TRUE/False] - VHS is IRE 0

F - [TRUE/False] - Laserdisc is IRE 0

G - [TRUE/False] - Cable / Satellite / Antenna sources are IRE 0

H - [TRUE/False] - CCE; MC; Procoder; TMPG; encoders feature an IRE 0 / 7.5 switch

more..

-vhelp 3142

BJ_M · Patron Joined: 30 Jul 2002 Location: Canada

lordsmurf · Posted: Feb 22, 2005 03:09

To further complicate matters ....

....

Let's take a gander at everbody's favorite MPEG encoder, TMPGENC PLUS... and that mystic setting .... you know the one...

Now... I know this isn't the prettiest VHS source in the world, but it was something I was converting (the tape is already dying, as you can see). Also note that I did some noise reduction and matted widescreen in the encodes, but the thing to pay attention to is the black/pastels changes by using this setting.

source (direct JVC DVD recorder MPEG capture, proper tonal values)

re-encode of MPEG .. unchecked ... blacks/whites/pastels remain the same

re-encode of MPEG .. CHECKED!... darks and black are pitch black (bad!) and the pastel blue turned several shades lighter, almost towards white

So..... what's going on here?

This "CHECKED EFFECT" is what happens on Panasonic E10/E20/E30 encodes. Too freaking bright.

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Another thing people keep forgetting is VHS was never "pure black" anyway. It's always a dark muddy gray at best. Yes, even commerial releases.
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BJ_M · Patron Joined: 30 Jul 2002 Location: Canada

thats why i said false for vhs ... dark muddy gray is a good description EXCEPT on broadcast quality s-video machines which can have a somewhat decent picture .. or my old sony 1000 svideo top of the line machine ....
I knew some stations that even used svideo (gag) for some things - on air
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gshelley61 · Frequent Flyer Joined: 19 May 2004 Location: USA

lordsmurf · Posted: Feb 22, 2005 14:57

Oh, and just as a note, the raw JVC source encode, as well as the new UNCHECKED TMPG encode, both look proper on the tv set. The original video is a little lighter than that, as it should be. I was unable to use a proc amp on it, as the source was too flawed, some goofy side effect happening.
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