White Level - Can't see moving bars - Page 7

Fair enough, it's what I've been trying to say and had originally posted four or five times already... IRE are not simply volts
In this thread I've really tried to avoid the DVD player variable altogether. A given DVD player does not change the DVDs encoded YCbCr nominal reference range. I guess by accident the YCbCr digital payload being discussed appears for some odd reason to align with my waveform monitor mV graticule.
I've only been trying to explain that a DVDs encoded Y' for example 16-235 correlates exactly to a (0-700mV) A/D and D/A unity model and that also aligns with my SMPTE SDI (10-bit) infrastructure. NO?

AGAIN I'm explaining what's encoded on the DVD disc. You are reaching back to the hypothetical I gave you in the other thread, which btw I specifically said for the ideal calibrated D/A. But all this does not matter anyway I've already listed above a mod for your standard def DVD player which will bypass the D/A process altogether, the mod would read the digital data directly and provide me SMPTE compliant SDI stream. My Leader HD-SD SDI waveform monitor will indicate 0V for digital code level 16 and .7V for the digital code value of 235.

Also an amplitude of (1-254) will measure ~800mV. With both negative and positive relative level, no matter what Chris thinks of my test equipment.

BTW it's just a coincidence that the SMPTE SDI P-P interface level spec is for 800mV. That is not a correlation with the encoded video signal levels.


Finally, Greg I do much appreciate the time!

All that everone else has really said is that in the analog realm, with a defined standard or known situation, IRE corresponds to volts.



Like above, with a defined standard, a digital signal corresponds to analog levels. You're not actually measuring mV with your scope from a digital input. Like gregr said, "Some instruments... represent digital signal levels as analog values". The scope shows a corresponding analog level, to the digital input, as defined by the selected standard.

In both of the above situations, they're each just defined relationships based on a standard.



YCrCb levels would generally correspond to analog levels through a chosen standard. The final analog representation depends on the standard selected. In a video playback chain the only place where analog levels actually arise from DVD is after a point of D/A conversion, and there are different standards for the conversion.



DVDs are encoded to digital levels. Volts are an analog unit. With a defined standard, analog units can relate to digital levels. If the standard is undefined, then discussing DVD in terms of analog levels makes no sense becuase there is not one single defined D/A conversion for DVD. Personally I consider discussing a digital medium in terms of what's actually encoded on disk to be less abstract, but if terms of conversion are defined then analog units can also relate to the stored digital information.

I have no idea what standard you are talking about, but FWIW I'm defining an MPEG-2 YCbCr standard color space digital encode.

601 mapping specifies that video black (0mV) is assigned a value of 16, and video white (700mV) a value of 235. This allows for reasonable footroom and headroom in the signal. The Y'CbCr color space is a logical choice for modern broadcast, since MPEG-2 compression operates in this color space. 700mV is also the maximum excursion required for a digital-to-analog converter (DAC) to generate SMPTE-compliant component video.

Voltage excursion for 8-bit DVD/Blu-ray DIGITAL ENCODING

Y Luminance is defined as being between peak white, 700mV (235). and black, 0mV (16).
CbCr Chroma is defined as being between max positive, 350mV (240), and max negative, -350mV (16).

The values above and below these are termed out of gamut.

All SD or HD (DVD/Blu-ray) productions employ engineers and color correction artist that reference similar if not the exact same wavefrom/vector monitors I use every day as well. These WF monitors have mV graticule markings that align with the video signal being encoded. They are calibrated to the same DIGITAL standards that I utilize.

My infrastructure is "calibrated” to the following Digital encoding standard:

HD-SD SDI SMPTE 259M, 272M, 299M.

EDIT/
Two standards, SMPTE 272M (for SD) and SMPTE 299M (for HD) define how audio is embedded into the ancillary space.

By the definitions in Digital Video and HDTV: Algorithms and Interfaces, 8-bit RGB of 235 is reference rather than peak white.

I'll let dlarsen (Dave) explain to you the concept of gamut error and legal/valid excursion. I see you still have issues with the accepted definition of IRE though

http://www.tek.com/Measurement/App_N...ponent_Puzzle/
“Eventually the IRE (later to be the IEEE) established a unit of measure for video signals. This “IRE unit’’ was defined as 1% of the video range from blanking to peak white, without reference to the actual signal voltage."

http://www.tek.com/Measurement/App_N...5W_15609_0.pdf
Preventing Illegal Colors
"For example, R'G'B' systems have an upper gamut limit of 700 mV and a lower gamut limit of 0 mV. If any channel of an R'G'B' signal exceeds either the upper or lower limit, a gamut violation exists."

"Legal signals, however, can be invalid in colordifference formats like Y'P'bP'r. The allowed range for the luma signal is 0 mV to 700 mV, and for the color difference signals P'b and P'r, the range is +/-350 mV."

Why on the prior quote do you say "IRE per definition is only correlated with the BLANKING LEVEL and reference white level" and now you say "blanking to peak white"? There is a disconnect there as to how Digital Video and HDTV defines the terms. Going by the terms in that book, 8-bit RGB of 235 is reference white and 254 would be peak white. Commercial DVDs appear to contain specular highlights above reference white as Poynton has commented.

If you wish to expain the discrepancy in how you're using reference and peak, that's fine. Otherwise I'm all for letting this thread die. Based on your prior posting history I figure that even after gregr pointed out how your comment regarding "IRE does not correlate to a fixed NTSC analog voltage" was incorrect, you would probably still contend that was an entirely true statement.

A valid signal is one that is within color gamut and remains legal when translated into any other format. IEEE makes proper use of the adjective (peak) in their definiton of IRE. For this reason HDTV and SDTV systems should NOT exceed the 0-700mV nominal gamut.

Defining Legal and Valid Gamut (From Tek link above)
“The term gamut has been used to refer to the range or gamut of colors reproducible by a television system when a scene is illuminated by a reference white (6500-degree illuminant D for NTSC/PAL and High Definition Systems).”

“Because the values of the R'G'B' signals directly represent these colors, the term gamut is often used to refer to the voltage range of R'G'B' signals. R'G'B' signals extending outside the specified voltage range, or gamut, may produce desirable color values (albeit outside the system color gamut) on a given picture monitor, but may be clipped or compressed in subsequent signal processing, distorting the color when displayed on another picture monitor.”

Please quote the words in ITU Rec. 601 that specify video black as 0 mV and video white as 700 mV? They aren't there because Rec. 601 does not discuss analog voltage levels at all. In fact it says (section 2.2), "In the circumstances when the component signals are not normalized to a range of 1 to 0, for example, when converting from analogue component signals with unequal luminance and colour-difference amplitudes, an additional gain factor will be necessary ...". It clearly anticipates the use of multiple conversions, some of which don't conform to the one case you continue to cite (which is when Y, Pb, and Pr all have the same 700 mV nominal excursions). In any case, there is nothing about a 700 mV analog amplitude in Rec. 601.

The reason for this confusion is because Rec. 601, an older standard, called 235 the peak white level. It also says (Table 2), "The signal level may occasionally excurse beyond level 235". Since it didn't make a lot of sense to say that the signal level could "excurse" beyond the peak level (and it caused confusion, often seen here on the forum), the terminology was changed/fixed in later standards, such as SMPTE 274 and ITU Rec. 709 (which are both HD standards). In SMPTE 274 and in Rec. 709, the corresponding 235 level is called reference white. (Perhaps tbrunet is stuck in the past? It sure seems a lot like "Groundhog Day" around here sometimes.)

Interestingly, SMPTE 170, which is an even older standard for NTSC composite analog video, also calls the corresponding white level the Reference White (defined as 714.29 mV for composite broadcast video), which really makes the "peak white" wording in Rec. 601 an unfortunate and poor choice of words (some say it was simply a terminology error that was never fixed).

http://broadcastengineering.com/mag/..._video_basics/
Figure 2
"The relationship between the E'Y, E'CB and E'CR analog component signal levels corresponding to a 100/0/100/0 color bars signal as specified in ITU-R BT.601, SMPTE 274M and SMPTE 296M. Click here to see an enlarged diagram."

E'Y = 0-700mV (Blk-Wht)
E'CB = +/- 350mV
E'CR = +/- 350mV

http://broadcastengineering.com/mag/..._video_basics/
Figure 2.
The relationship between the E'Y, E'CB and E'CR analog component signal levels corresponding to a 100/0/100/0 color bars signal and the 10-bit and 8-bit Y, CB and CR digital sample values, as specified in ITU-R BT.601, SMPTE 274M and SMPTE 296M. Click here to see an enlarged diagram.

235 = PEAK LEVEL
16 = BLANKING

Michael Robin, a fellow of the SMPTE and former engineer with the Canadian Broadcasting Corp.'s. He is co-author of Digital Television Fundamentals, published by McGraw-Hill, and recently translated into Chinese and Japanese.

That's a magazine article, it's not Rec. 601. Quote the section of Rec. 601 that you claimed specifies peak (reference) white as 700 mV. It isn't there. It gives normalized signal levels (Table 3), i.e. 1.0 for E'Y, not 700 mV.

Good luck with that observation.

“Signal Characteristics: All HDTV scanning formats originate as component analog gamma corrected E’ subscript R,G,B signals. These signals may be encoded into component analog E’Y, E’Cb and E’Cr. All analog signals have nominal p-p analog signal amplitude of 700mV corresponding to a 100/0/100/0 color bar signal.”

Hey Greg, I need to calibrate my analog waveform monitor so that I can adjust the black level for a given video frame that is to be encoded onto a standard def (ITU-R BT601) DVD release. Are you telling me I can’t do that because it “DIGITAL” and there are no volts envolved?

Can you then describe to me how I’ve calibrated my plant incorrectly? According to Michael Robin that books author, you do NOT know what your talking about.

Thanks in advance!

According to Figure 2 in that Broadcast Engineering Mag link above (note: click to enlarge icon), Michael Robin's math shows:

0mV = 16 for 8-bit (decimal)
700mv = 235 for 8-bit (decimal)

Again you quote magazine articles. The Y' component corresponding to 235 is not called the peak level in Rec. 709 or SMPTE 274, it is called reference white. See section 5.4 and 10.5 of SMPTE 274. See Table 5, item 5.1 of ITU-R BT.709 (i.e. Rec. 709).

You said you use SMPTE 274 in your work, so quit quoting magazine articles and give us sections of SMPTE 274 that use the term "peak white" rather than "reference white". (As I already said, the term "peak white" is used in Rec. 601.) And tell us what section of Rec. 601 defines peak white as 700 mV as you claimed (it doesn't - it defines no specific standard for analog signal levels - only normalized signal values with peak white = 1.0, but SMPTE 274 does because it defines a specific standard for digital and analog component video signals.)

When your claims are challenged, you say the standards support your claims. Then when I give you references in the standards you give us quotes from magazine articles.

More magazine quotes (talking about SMPTE 274). Quote the section of ITU Rec. 601 that you claimed said that peak white was 700 mV.


Digital levels are not in volts. That's pretty damn elementary. A waveform monitor that accepts digital signals (i.e. SDI) can have a graticule that shows equivalent analog volts in any standard that relates digital levels to analog volts, and sometimes they include more than one standard. A waveform monitor may have multiple digital to analog electronic graticules, which show different analog levels for the same digital level.


Or you don't comprehend what he is talking about.

I've wasted enough time with this. No more replies from me.

That is a word for word quote from Michael Robins's published McGraw-Hill book.

http://books.google.com/books?id=BkC...um=4&ct=result
Digital Television Fundamentals

Explains relevant SMPTE and CCIR-ITU standards

I specifically asked you in the process of color correction or encoding a DVD master. For example:

Can professionals reference a calibrated analog waveform? Below I've defined in detail exactly an 8-bit (decimal) digital YCbCr component signal and how it correlates to a calibrated component waveform monitor per ITU-R BT.601 standard.

Y' = 16-235 = 0V-700mV
CB, CR = 16-240 = +/-350mV

Greg the question IS rhetorical btw, not only is it possible but it's done on a daily basis except the medium now is Blu-ray.

OK, that quote was from the book Digital Television Fundamentals, which I have. But that quote is about HDTV formats, it says "All HDTV scanning formats ...". You were writing about Rec. 601, an SD format, not an HD format. So that quote has nothing to do with what you originally wrongly claimed Rec. 601 said about 700 mV (white) and 0 mV (black). So once again, quit taking quotes from books and magazines out of context, and tell me where in Rec. 601 you claim it says the analog voltage level is 700 mV. If you can't do that, then admit it doesn't, and quit posting erroneous information.

Also look at the source you quoted, Digital Television Fundamentals, figure 2.83 on page 121 (my 1998 edition). It shows 4 different analog component video signal standards. One is NTSC related with 714 mV white level and 53.55 mV black level, another is EBU N10 with 700 mV white level and 0 mV black level. Another is Betacam with 714 mV white level and 53.55 mV black level, and another is M II with 700 mV white level and 53.55 mV black level. (The last black level is an error in the book, BTW, it is actually 52.5 mV, and the other black levels are actually 53.57 mV rather than 53.55 mV.)

So 3 of the 4 standards used as examples in the book you selected to support your claim, disprove your claim that reference white is ALWAYS 700 mV and black is always 0 mV. The book simply lists a few of the analog component video standards that prove you are wrong, as I have been telling you.

Now I have to move on and do other things. So unless you are willing to post information directly from the Rec. 601 standard, please stop posting on this topic. Quit posting information out of context from secondary sources that does not apply to your original claims about Rec. 601.

I would NOT be soo quick to point out Michael's "errors" without first noting his obvious expertise. If you want to correct the more significant error btw, how about the table in Figure 2



Greg if you ever manage to click on the icon to enlarge the diagram (Fig. 2) provided by Michael, you will note the 8-bit (decimal) code value 16 and 235 respectively appear to correlate exactly to a 700 mV p-p waveform..NO? The same seems true of the 16 and 240 codes for CB & CR?


Send questions and comments to: michael_robin@primediabusiness.com

Paaalease!

The Broadcast Engineering Mag article is NOT “out of context” and it’s now obvious to everyone Michael Robin knows his AC from his DC

ITU-R BT.601 (Y’) component has the following p-p analog values for 8-bit Video

1 = -47.9 mV
16 = 0 V
235 = 700 mV
254 = 763.13 mV

gregr's comments appear rather clear to me. He appears to be saying this is acutally defined by SMPTE 274 rather than Rec 601. Looking at "Definition of the digital signals Y, CR, CB, from the primary (analogue) signals" from http://inst.eecs.berkeley.edu/~cs150...nts/ITU601.PDF it appears that Rec 601 uses analog levels of 0v for black and 1v for white like he said with terms to adjust between different systems. I really have no interest in reading SMPTE 274, but it seems clear that Rec 601 doesn't use the quoted terms like you've said.



Thanks for the clarification. If nothing else I found your comments interesting.

I have to ask the question if you don't mind..

Did you even look at the diagram for Fig. 2 that I posted ten times already..at all?

Can you please report what value Michael Robin suggest (author Broadcast Engineering article) an 8-bit Y' (decimal) code value 235 represents i.e.

Is it 700 mV?

Have you read the references for that item? It clearly says "as specified in ITU-R BT.601, SMPTE 274M and SMPTE 296M." Rec 601 is not where those voltages you keep refering to are defined. Rec 601 references 0 to 1v for black to white with the formulas it uses. So have you even read Rec 601 that I linked?

http://www.testequipmentdepot.com/te...al/wfm5000.htm
WFM5000
Supports HD-SDI (SMPTE 292M) and SD-SDI (ITU-R BT.601) monitoring applications.

If the machine above does not indicate 0V and .7V respectively for a nominal Y' Blk-Wht signal i.e. (16-235) 8-bit Rec. 601 video.


"it's broke"!

Yep and I'll play your game. Please provide me a link to one Y'Cb'Cr' component waveform monitor used by industry pros like me, that will indicate Blk-Wht (Y') signal that in Volts i.e. a 1V p-p waveform representing a standard reference color bar signal.

Well, I wasn't playing any game. I wanted to see what exactly is defined by Rec 601, so I looked at the document I linked. It appears to define the digital levels and it defines "primary analogue signals" that correspond with the equations it gives. Rec 601 does not appear to define typical component video, which is the key of your comments. If you've read Rec 601 then it seems to me you should either know that component video is not used in the definition of the standard, or else if that's not the case then maybe you should reference where in the standard it's defined. The component voltages you keep bringing up have to be defined somewhere, but my take is that it's not in Rec 601 like your general comments would suggest. I have no issue with how your meter can have a relationship between analog voltages and digital signals, but I'm not so sure by your communication that you understand from where such a correlation arises.

http://broadcastengineering.com/mag/..._video_basics/

Whether you or Greg understand the process of (DVD, SDTV, or HDTV) content mastering or not, believe me they are ALL looking at an analog waveform, be it RGB or YCbCr. For 8-bit or 10-bit video the nominal reference range is 0-.7V

The production artist/engineer doing color correction needs real time confidence as he/she adjusts the image. If the WF indicates the Black level i.e. is offset +/- from (0V) the blanking level, it's really an accurate measurement.

alluringreality, that is exactly correct. Now that you have provided an on-line link to Rec. 601, there is no excuse for anyone to continue to post erroneous information about what is contained in Rec. 601.