My take on orbs / hard clipping

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John Brawley

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My take on orbs / hard clipping

PostFri Sep 13, 2013 9:48 am

So it seems there was a "calibration" problem with some of the first Blackmagic Design Pocket Cinema Cameras shipped. Many have reported a kind of hard clipping, often described as ORBS or BLOOMING.

It's worth looking at exactly what this is and why it happens.

CMOS sensors are particularly susceptible to this to varying degrees, and sensors have various design features to reduce the effect like "anti-blooming drain". It can be mitigated, but not entirely - it's just physics. If you have a bazillion more photons than you can be registered hitting a given pixel, the energy has to go somewhere !

The problem is that once you describe something as an "orb" then you can start to see orbs in almost any footage including those from cameras that aren't Blackmagic Cinema Cameras.

Orbs can be created through any number of factors and are greatly affected by sensor size, lenses, exposure, where you set focus and what kind of lights or "orb" sources you're shooting.

So lets' say orbs are normal. You get them whenever you have a small point source like the bare filament of a bulb at a distance or a small glint from the sun off a car. It could also be lights at a great distance that are out of focus. They are usually super white or beyond clipping. Once out of focus they become even more "orby"

Once the sensor clips then it renders that detail white.

What was different here is that specular highlights and small sources with extreme overexposure can cause a kind of hard clipping with the Blackmgaic pocket cinema camera, as opposed to "orbs".

It barely was present in my own early footage and it seems to have been worse in the production versions of the camera.

BMD have come up with a fix for this hard clipping in the space of a couple of weeks. I've got both an uncalibrated production camera and a calibrated production camera so I thought I'd shoot them side by side with a bit of a highlight orb torture test.

One thing I've found amazing is that once you start looking for "orbs" you start seeing them everywhere ! Various forums have been rife with "orb spotting" and many of them have really just been regular clipping on small point sources.

As I mentioned, it's normal to have a kind of orb with a hot point source of light when you clip or overexpose certain objects. Look at my iPhone photo below in the same setup I've tested with below.

This is why I've never been comfortable with calling it ORBS or BLOOMING because it doesn't really accurately describe the fault and creates a false impression of a problem. To my eyes, it's a "HARD" or HARSH" clipping that occurs on overexposed or super white point sources of light. So we're looking for HARD clipping and HARD clipping that eats into foreground images, not ORBS.

Below's a shot I took with my iPhone. Would you call this an ORB fault ? I wouldn't.

MirrorBallOrb.jpg
MirrorBallOrb.jpg (827.43 KiB) Viewed 1936 times


So here's what I did to try and create the effect.

I got a mirror ball and pointed a 100w dedo at it. Right beside it in-shot is another 150w bare dedo bulb.

In the foreground I placed two plants, with the middle ground slight obscuring the 150W dedo in the deeper BG.

Pocket.jpg
Pocket.jpg (53.41 KiB) Viewed 1936 times


I wanted to set up a few "orb" scenarios and look at both re-creating the effect and also showing that there is a more "normal" kind of clipping orb. Again look at the image below, taken with my iPhone. Note the clipped "orb" highlight in the mirror ball.
SmallSpecularHighlight.jpg
SmallSpecularHighlight.jpg (663.46 KiB) Viewed 1936 times




So below is an edited version of what I shot. You can download the original ProRes files https://copy.com/BawphaZhKR9B.

I've shown both the un-calibrated camera and a calibrated camera. You'll notice that it's very difficult to pick much of a difference on the mirror ball's occasional hits from the dedo. Where you'll see the hard clipping most in the first clip with the 150W dedo that's in shot and you'll notice it actually has a hard and ugly edge and kind of "eats" into the foreground flower.

In the calibrated camera, you notice that the 150 lamp is still clipped or blown out. You could even say it's an orb too, but there is detail in near clipping, and you can also make out more of the flare. There's also none of the circular hard edged clipping that eats into the flower in foreground you see in the previous example. I also did some small blow ups and a large scale up as well so you can really look at the hard clipping close.

You should also note, that the black sun effect is also now gone from the image in the "calibrated" camera. The next firmware release should incorporate this.

Finally, just because I hadn't had the Zeiss CP2 50mm Macro on before, I did a quick grade on the footage showing off some lovely close detail.

Vimeo clip here...

John Brawley
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Marcel Beck

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Re: My take on orbs / hard clipping

PostFri Sep 13, 2013 10:02 am

Thanks John for taking the time to produce the comparison
Marcel Beck
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adamroberts

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Re: My take on orbs / hard clipping

PostFri Sep 13, 2013 10:04 am

Thanks John

A nice explanation.

Cam B is exactly as I'd expect the highlights to be handled.



I totally agree with this:
John Brawley wrote:One thing I've found amazing is that once you start looking for "orbs" you start seeing them everywhere ! Various forums have been rife with "orb spotting" and many of them have really just been regular clipping on small point sources.


I've seen many people post stuff saying they have ORBS when all they have is clipped highlights that even have a soft roll off.
Last edited by adamroberts on Fri Sep 13, 2013 10:06 am, edited 1 time in total.
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John Brawley

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Re: My take on orbs / hard clipping

PostFri Sep 13, 2013 10:06 am

adamroberts wrote:
I've seen many people post stuff saying they have ORBS when all they have is clipped highlights that even have a soft roll off.


Yeah it's driving me nuts !

jb
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adamroberts

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Re: My take on orbs / hard clipping

PostFri Sep 13, 2013 10:09 am

John Brawley wrote:Yeah it's driving me nuts !


Totally. When the highlights clip like in Cam A footage it does look nasty but the but the way is rolls off in Cam B very close to how film rolls of when over exposed.
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Mac Jaeger

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Re: My take on orbs / hard clipping

PostFri Sep 13, 2013 3:23 pm

John, thank you very much for this thorough explanation, and especially the instructive examples. Obviously your calibrated camera also had the new firmware applied that erradicates the black spot as well?

Bytheway: i'm sure you didn't mean to, but you might have given some people a minor heart attack when you wrote
John Brawley wrote:I've got both an uncalibrated production camera and a calibrated production camera
... ;-)
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Austin Reed

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Re: My take on orbs / hard clipping

PostFri Sep 13, 2013 3:40 pm

Thanks for the explanation!
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Steve Holmlund

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Re: My take on orbs / hard clipping

PostFri Sep 13, 2013 3:47 pm

John, yes, thanks for the time and explanation. I take your point about seeing orbs everywhere. Found myself looking at headlights last night and realized there was a point when cars approached where even my eyes seemed to create them.

Hard clipping does seem to be a better description esp. when it eats into the foreground image. What is a little disconcerting is the recent posting from a recent bmcc mft buyer with an example of hard clipping that apparently isn't present in earlier units. Realize the jury's still out on that one but it makes one wonder about production tolerances/variations.

Thanks again.
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Manu Gil

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Re: My take on orbs / hard clipping

PostFri Sep 13, 2013 3:51 pm

Thanks John.

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