This IS the Avid L2: Re: [Avid-L2] Safe Color Limit Inconsistent Black Level between systems?

Friday, September 23, 2016

Re: [Avid-L2] Safe Color Limit Inconsistent Black Level between systems?

So I got a QC report back saying there was slightly elevated blacks during black fades and under credits. I have my usual Safe Color limit set at RGB 16-235 and the composite now set to 0. I have now found that having composite Lum L set to 0 generates slightly elevated black and also setting the RGB Gamut L to 16 generates the same elevated blacks. WTF? If I set composite Luma L to -.1 no black elevation and similarly if I set RGB Gamut L to 15 it stops the elevated black. I've been setting 16-235 for my safe color limit for ever and never really paid attention to the composite Luma L until I saw the 7.5 setting cause really elevated black when using the DNxIO. So why the hell is this off now?

With all this in mind I did switch my home system back to the NitrisDX to see if the DNxIO was behind the slightly elevated black but F me skipping the Nitris DX is showing the same slightly elevated blacks. The only difference is that with the NitrisDx hooked up the composite Luma L slightly elevates the blacks when it's set to 7.5 but if I set it to 7.4 the black is pefect 0mV. So the difference between NitrisDX and DNxIO and more than likely any other BM card as well as other 3rd party IO is clearly about the Composite Luma L 7.5 setup parameter.

I can't imagine I've been missing this slightly elevated black for the last 4 to 5 years when safe color became necessary for file based delivery. I will have to run the same tests back on my NitrisDX at work. It has the same Mac OS and MC 8.5.2 whereas my home system is 8.5.3. I have nothing like Perian installed that I know of that would cause this. I see the elevated blacks on my scope and QC saw it on the file I generated so it's there. Anybody else see this behavior?

---In Avid-L2@yahoogroups.com, <bigfish@...> wrote :

Many years back I had the same issue when I used a saved safe color from a 59.94I or SD project in a PAL project. In that case it was all Avid hardware of the NitrisDX variety. So while it seems to be hardware related in my current case and yours going back about 6 or so years I had the same sort of behavior with all Avid hardware. Maybe something is different now.

It's curious how the hardware effects an internal level render this way. It seems as if there is some aspect of the old safe color legalizer hardware function on the old meridian Symphonys.

---In Avid-L2@yahoogroups.com, <mactvman@...> wrote :

Hello John,

This is a bug we have tracked at my facility as well, between Nitris DX systems and Aja Kona 3 I/O cards. It seems to be a bug relating to previous versions of the safe color effect, and how it is interpreted differently on systems with different i/o hardware.

For our promo work we routinely do color and final output in the AVID, with a safe color limiter as a top layer and we keep one handy in a bin, with the settings we like.

When we upgraded to Media Composer 8.5.3 we noticed the issue, only using the older saved Safe Color Limiter effect. We replaced it with a new version made from the MC 8.5.3 effects pallet, and the systems are once again consistent, between Aja i/o and Nitris DX.

Dave Hogan

Burbank, CA

On Tuesday, September 20, 2016 12:13 AM, "John Moore bigfish@... [Avid-L2]" <Avid-L2@yahoogroups.com> wrote:

At work I'm on a MacPro mid 2010 tower upgraded to 12 core OS 10.9.5 running MC 8.5.2 with a NitrisDX. I have a safe color limit on a sequence set to 422 composite -20, 110 default and RGB limit set 16 to 235. I rendered this fine on the work system.

When I take the sequence home I'm on a mid 2012 MacPro 12 Core now running a DNxIO MC 8.5.3 OS 10.9.5. I find that when I unrender the safe color limit the black level is elevated. If I drop on a new safe color and use the same settings all is correct with no black level elevation.

Finally after comparing the two effects I noticed the Luma L parameter is 7.5 on the safe color that elevates the black when it becomes unrendered and the new safe color has a Luma L value of 0. Now I've never even paid attention to those parameters before but I have seen a similar issues over the years and had never put my finger on it. The first time it happened it was when I applied the safe color limit from an 29.97 project in a Pal Project. I had figured it had something to do with a lack of setup in Pal and just rebuilt the effect. Since then I have seen this behavior from time to time.

Given my system is virtually identical to my work system the only difference is at work it's NitrisDX and at home now DNxIO. I also have a NitrisDX on my home system but have switched to the DNxIO for this 4 K PIxel hunt I'm in the middle of. Before I had a Black Magic SDSDI card and I had occasionally seen this same issue.

Is there something in the Avid IO hardware that would account for a different interpretation of the Luma L parameter in the safe color limit effect? Given I never knowingly set Luma L to 7.5 I figure it must be a by product of the video output settings composite output where you can choose to add 7.5 ire on composite setup. Could that setting effect the default value assigned to Luma L in the Safe color effect?

Given the video output doesn't have the analogue output adjustments in Avid's video output when running 3rd party IO I'm beginning to think that having Luma L at 7.5 on a Nitris DX system gets interpreted as no black level elevation whereas the same setting when using BM and perhaps other manufactures IO hardware results in elevated black. Does this make any sense? I can't see any other explanation as to how it rendered to correct black levels on the NitrisDX system but doesn't render to correct black levels on the DNxIO system. At least I finally found the parameter that is causing it bit how come it doesn't cause elevated blacks when rendered on the Nitris DX system the sequence was created on?

John Moore Barking Trout Productions Studio City, CA bigfish@...

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Posted by: bigfish@pacbell.net

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