FS7: Inconsistent behavior of Zebras ??? What am I missing?

B

broughtonfilm

Well-known member
While testing the camera I noticed an odd behavior of zebras. Feels like Zebra 2 sometimes is not showing in areas where I'd expect it to show.


I did this test. Set both zebras to 94%, Zebra 1 Aperture Level is not narrow, it is set to 20 (to minimize it as a factor in how two zebras are displayed). Camera is pointed at the same target. While toggling between Zebra 1 and Zebra 2, the same exact area of the target is striped with Zebra 1 but when I switch to Zebra 2 it is not (for the test purposes you can do this back-and-forth toggling conveniently by being in Zebra Select menu). Again, both zebras are set to the same exact value. The difference is not because of narrow Zebra 1 Aperture Level setting , it is set to 20. Now, in order for Zebra 2 to show stripes in the same area of the target, its value needs to be significantly lowered (approx. 8-10 IRE on average). Of course, I see no real-life situation where both zebras would be set to the same value, this is simply to test if they are matching and seems that they are not.

EDIT: I thought that the inconsistency was caused by too high zebra setting for this particular LUT (LC709A). I performed the same test with much lower Zebra IRE settings. Both zebras are set to 74% which should be well within LC709A's IRE range. Nope, same discrepancy between two zebras, again, it is about 8-10 IRE difference.


What am I missing?



My settings:


Format: XAVC-I , 1920x1080 23.98p
Mode: Cine EI
Gamma: SLog3
Color Space: S-gamut3.Cine / SLog3

Monitor LUT
Look Profile Sel. : LC709A
SDI1 & Internal: MLUT OFF
SDI2: MLUT OFF
HDMI: MLUT OFF
Viewfinder: MLUT ON
 
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I don't know but seems a better way to test would be to compare to a waveform with realistic levels for the zebras.
 
I think you are misunderstanding how the two different zebras work.

Zebra1 @ 94% with an aperture of 20 means that the zebras are going to start appearing at 84%. While Zebra2 @ 94% won't show zebras until 94%.
That is why you have to set Zebra2 8-10 IRE lower so it kicks in at 84% to match Zebra1.

You might be interested in my Master Class for more information. It covers the zebras in detail.

http://www.vortexmedia.com/DVD_FS7.html
 
Doug Jensen said:
I think you are misunderstanding how the two different zebras work.

Zebra1 @ 94% with an aperture of 20 means that the zebras are going to start appearing at 84%. While Zebra2 @ 94% won't show zebras until 94%.
That is why you have to set Zebra2 8-10 IRE lower so it kicks in at 84% to match Zebra1.

You might be interested in my Master Class for more information. It covers the zebras in detail.

http://www.vortexmedia.com/DVD_FS7.html
Click to expand...

Thanks, I wasn't sure if 20% aperture adds a margin on both sides of set value, I thought it was only above. It still does not explain the difference because I just checked it with Zebra 1 Aperture level set to 3%, much narrower. Zebras don't match and the difference is way more than half of Zebra 1 Aperture level value.

I've been eying your master class for a while, I'll definitely use it soon, it looks good.

Thanks
 
Doug Jensen said:
I think you are misunderstanding how the two different zebras work.

Zebra1 @ 94% with an aperture of 20 means that the zebras are going to start appearing at 84%. While Zebra2 @ 94% won't show zebras until 94%.
That is why you have to set Zebra2 8-10 IRE lower so it kicks in at 84% to match Zebra1.

You might be interested in my Master Class for more information. It covers the zebras in detail.

http://www.vortexmedia.com/DVD_FS7.html
Click to expand...

Also, do you know what Zebra 2's default Aperture Level is?
 
broughtonfilm said:
Also, do you know what Zebra 2's default Aperture Level is?
Click to expand...

To answer my own question, looks like the Aperture Level setting of 13 is a default Zebra 2 value. This is based on a comparison of shapes of striped areas . When Zebra 1 Aperture Level is set to 13 it seems to match that of Zebra 2, patterns look similar.
 
Doug Jensen said:
Zebra2 does not have an aperture. May I suggest the video again? :-)

http://www.vortexmedia.com/DVD_FS7.html
Click to expand...

I know it does not have an Aperture as a user accessible setting, but one way or the other it must have some kind of aperture to which it defaults (factory preset). If zebra 2 does not have Aperture then why does its pattern cover range of tones instead of just one narrow luminance value? It is not just one value of luminance but instead a range, it does have some tolerance (in a sense that it is not as precise as Zebra 1 set to Aperture Level of 1-3). That is the value that I thought was equivalent of Zebra 1's Aperture setting of 13.

I promise I will watch your DVD, :).
 
Doug Jensen said:
I think you are misunderstanding how the two different zebras work.

Zebra1 @ 94% with an aperture of 20 means that the zebras are going to start appearing at 84%. While Zebra2 @ 94% won't show zebras until 94%.
That is why you have to set Zebra2 8-10 IRE lower so it kicks in at 84% to match Zebra1.

You might be interested in my Master Class for more information. It covers the zebras in detail.

http://www.vortexmedia.com/DVD_FS7.html
Click to expand...

Ok, I tested again and of course Doug's above explanation was right on the money. "Duh" is the word I sometimes hear in situations like that. This is even before watching the DVD, watching it will be a bonus. Topic closed.
 
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Zebra 2 is that point upwards, zebra 1 is both directions. Honestly, watch Doug's video. It's worth it for those hidden gotchas, of which the are several.
 
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