Blackmagic Forum

Tue Apr 13, 2021 10:55 am

My brain hurts reading all about 18% gray being calibrated to 42IRE or some such settings.

I shoot with a Panasonic GH5 with a profile of vLog. I shoot at 4k/422/10bit/ALL-Intra,400Mbps
The waveform is a small graph with solid and dotted horizontal lines. There are no numbers on this scale.

I also have a X Rite Passport Colour Chart

My Atomos Ninja V has a waveform with horizontal lines and a scale going from 0 to 100

My Davinch Resolve has a Waveform Scope with horizontal lines a scale going from 0 to 1023 and a dotted line at scale point 512.

I have read many, many, many reviews and forums but nobody has mentioned where the IRE Sweet-spot magic number fits onto a Waveform. And I can not find where a Waveform shows an IRE scale on my camera, monitor or Editing software.

I have the tools to read and plot a specificity printed tone of grey on a card, but I can not find anywhere on the internet to tell me where this specific tone of grey should be represented on a Waveform to achieve good exposure.

Could somebody please tell me in IDIOT TERMS where 18% (Middle) grey, on my X Rite Passport should sit on the Waveforms on my Panasonic GH5, Ninja V and DaVinci Resolve?

Its a simple question, so why can't I find the answer?

Tue Apr 13, 2021 11:18 am

For V-Log the correct Middle Gray is at 42% IRE on camera and external waveform monitors.

Don't rely on the Exposure Meter of the GH5, its readouts are 1 stop overexposed for the HLG and V-Log L profiles.

If you are using the Color Checker Passport Video, the middle gray chart is easily visible. For the regular color Checker Passport refer to the following:

https://xritephoto.com/ph_product_overv ... ortID=5097

In Resolve, the settings you use will have an impact what values you should be looking at on the waveform.

If you are using RCM with DRT enabled and set input to V-Log and output to Rec.709 Gamma 2.4, the waveform should be around 41 IRE (same goes for ACES). If you have DRT disabled, and output to Gamma 2.4, the waveform should be around 49 IRE

On the GH5, the 3 solid lines represent 0, 50% and 100%. You should be able to work out 42 from there. Have a look at the picture midway down my write-up:

https://xtremestuff.net/recording-editi ... mma-part-1

As for Resolve, change the waveform type to percentage. No more headaches from there.

Tue Apr 13, 2021 11:23 am

That is an excellent question.
Wikipedia says https://en.wikipedia.org/wiki/Middle_gray
If you make a solid color in Fusion (I chose rgb(128,128,128)) your grey color is exactly at the 50% mark in sRGB.
18% gray (as defined at rgb(118,118,118)) is slightly lower, according to the color values: 46.274%.
Fusion Background at rgb(118,118,118) is 0.4627450980392, 0.4627450980392, 0.4627450980392
If you have 1024 values, the point to aim for is 473,8509803921408 (0.4627450980392*1024)

Tue Apr 13, 2021 11:32 am

RikshaDriver wrote:As for Resolve, change the waveform type to percentage. No more headaches from there.

I'd be most grateful if you could explain how to do this?

Cheers

I will also read your review.

Tue Apr 13, 2021 11:35 am

The lemming wrote:
RikshaDriver wrote:As for Resolve, change the waveform type to percentage. No more headaches from there.

I'd be most grateful if you could explain how to do this?

Cheers

I will also read your review.

3 dots -> Waveform scale style -> Percentage

Tue Apr 13, 2021 11:52 am

Way too slow, I turn around for a minute. One can always use the OFX CST to invert the space and determine the desired input. I found the white paper on vlog and verified it's indeed 42.

https://pro-av.panasonic.net/en/dvx4k/p ... ol6_en.pdf

Good Luck

Wed Apr 21, 2021 10:03 pm

That's not the V-Log whitepaper.

This is the actual whitepaper:

https://pro-av.panasonic.net/en/cinema_ ... -Gamut.pdf

Fri Apr 23, 2021 6:18 pm

Mads Johansen wrote:
The lemming wrote:
RikshaDriver wrote:As for Resolve, change the waveform type to percentage. No more headaches from there.

I'd be most grateful if you could explain how to do this?

Cheers

I will also read your review.

3 dots -> Waveform scale style -> Percentage

In waveform the only options that I have are:
Low pass Filter
Video Level Scopes
Display qualifier focus
Ratio
Quality

No option for percentage

Sorry

Fri Apr 23, 2021 6:42 pm

You don't have this?

Fri Apr 23, 2021 7:00 pm

In the three dots menu placing your curser over or clicking on Waveform Display Style will reveal a sub menu with amongst other things, Percentage.

Sat Apr 24, 2021 7:17 pm

Mads Johansen wrote:You don't have this?

Sadly not.

I am using version 16.

Resolve 17 is just not stable on my computer.

Sat Apr 24, 2021 7:36 pm

For what seems like a very simple question with a very simple answer, I am just as confused.

To recap is it fair to say that "18% Grey" is in the middle of the Waveform, irrespective of scale values of IRE, percentages or grotes.

I have the X-Rite Video Passport. with the three solid blocks of white, grey and black, where should they sit on the Waveform?

Please don't confuse me with quoting IRE Levels, please make it simple and say where they sit on a Waveform chart that uses 1023 levels as my scale.

Sadly I can't find a way of showing percentages with my Resolve version 16.

Mon Apr 26, 2021 7:28 am

The lemming wrote:For what seems like a very simple question with a very simple answer, I am just as confused.

To recap is it fair to say that "18% Grey" is in the middle of the Waveform, irrespective of scale values of IRE, percentages or grotes.

I have the X-Rite Video Passport. with the three solid blocks of white, grey and black, where should they sit on the Waveform?

Please don't confuse me with quoting IRE Levels, please make it simple and say where they sit on a Waveform chart that uses 1023 levels as my scale.

Sadly I can't find a way of showing percentages with my Resolve version 16.

Yes. 18% grey in sRGB is exactly in the middle of the waveform.

I have made a diagram with 18% grey in sRGB, 18% grey card, pure black and pure white where you can see the waveform for each in a 10 bit (0-1023) waveform.

The reason for 18% grey in sRGB and 18% grey card is shown in https://en.wikipedia.org/wiki/Middle_gray

Mon Apr 26, 2021 7:38 am

Middle Gray for sRGB is actually 46% - around 472 on a 10 bit scale
Middle Gray for pure Gamma 2.4 is 49% - around 500 on a 10 bit scale
Middle Gray for Rec.709 is 41% - around 415 on a 10-bit scale

Your output and timeline settings will have a factor in determining what you should be aiming towards.

As I mentioned earlier, if you're using a Color Managed workflow to output Rec709 Gamma 2.4 with Input/Output DRT enabled, then middle gray is around 415

if no DRT, then Rec709 Gamma 2.4 is around 500

Mon Apr 26, 2021 7:46 am

RikshaDriver wrote:Middle Gray for sRGB is actually 46% - around 472 on a 10 bit scale
Middle Gray for pure Gamma 2.4 is 49% - around 500 on a 10 bit scale
Middle Gray for Rec.709 is 41% - around 415 on a 10-bit scale

Your output and timeline settings will have a factor in determining what you should be aiming towards.

As I mentioned earlier, if you're using a Color Managed workflow to output Rec709 Gamma 2.4 with Input/Output DRT enabled, then middle gray is around 415

if no DRT, then Rec709 Gamma 2.4 is around 500

Do you have sources for those statements?

Mon Apr 26, 2021 8:14 am

Rec.709 is the ITU specification
sRGB is the sRGB specification

Just look up the transfer function for each.

Pure gamma 2.4 is simple... 0.18 ^ (1/2.4) = 0.489 * 1023 = ~ 500

I just did the math (I'm an Engineer).

Mon Apr 26, 2021 10:20 am

This ^

Now if someone could explain to me slowly, why encoding to gamma 1/2.4 is a thing these days, I would be happy. I always feel some eerie discomfort when I read from same sentence about obsessive calibration and then encoding data with some absolute random function while producing for some well defined output (BT.1886 for example).

Where is 18% Grey on a waveform?

Where is 18% Grey on a waveform?

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