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Cine Meter for iPhone: how to... copyright © 2013 Adam J. Wilt  
A light meter with a waveform monitor and a false-color picture

How To...


Matrix metering

Shooting this scene in matrix mode captures most of the tonalities but leaves the subject a bit underexposed.

Spot metering

Switching to spot mode metering and putting the “spot” on the painting bring up the levels: a stop brighter on the meter, about a stop and a third in the picture and on the waveform (this is not unusual; the meter and the displays don’t always track each other, as explained here).

Using the spotmeter mode to capture correct

Using Cine Meter’s spot mode, we can get a reading on the backlit cat and avoid too much influence from the bright sky and the low winter sun.

False Color confirms the proper exposure

False Color mode lets us double-check light levels and gives us a graphic portrayal of our danger zones. The green shows us that the cat is nicely placed around the midgray tones; the darkest bits of the shaded foliage to the right are liable to lose shadow detail, and the sky... well, the sky is going to clip, no two ways about it. If I planned to use an ND grad on this shot, I could hold it in front of Cine Meter and see right away what sort of difference it would make.

It’s important to note that the pictures and the light meter don’t track each other precisely, due to the particular exposure-level programming in your iDevice’s camera module.

It just so happens that in this example my midgray level is smack-dab on the cat at this meter reading, but practically speaking, I’d take a meter reading for my production camera, then I’d separately “trick” the camera into putting my midgray tones where I wanted them (by tilting the camera more towards the bright sky or the dark foliage until the exposure changed to what I wanted). I’d then lock that exposure and look at the false-color and waveform displays to see what the rest of the scene is doing.

Barney on a badly-lit greenscreen

Here, our subject is lit from one side with a KinoFlo Diva-lite 400. The waveform monitor shows how much exposure variation there is side-to-side (the tilt in the green and blue lines) as well as top-to-bottom towards the edges of the image (the fattening-up of the green and blue lines at the sides of the waveform monitor image).

It’s interesting to note that even though I haven’t locked white balance in this shot, the camera has auto-balanced on the rabbit’s white fur (and/or the rabbit’s tan fur counterbalances the greenscreen’s green in the camera’s tiny mind), so the picture looks reasonably correct.

The waveform monitor shows that the blue reflected by this particular greenscreen (a sheet of green poster board bought at an art store) is quite strong; it’s only about a stop under the green, though red reflection is admirably absent.

The scene looks fine to the eye—it’s obvious which parts are rabbit and which parts are greenscreen—but Cine Meter shows us how sloppy the green lighting is. Yes, I’m sure we could pull a key in one pass, if we didn’t care about fine detail... but if we don’t even out the lighting, our VFX guy will be very cross with us. 

False-color of Barney on the badly-lit greenscreen

False-color mode confirms that this exposure is probably OK, even if the balance isn’t great (you’ll observe that the meter reading is ⅓ stop darker than in the previous screenshot, even though the image is a little brighter. Remember what I said I said about the camera exposure not always tracking the meter reading?). There’s a clipped specular kick in Barney’s eyelight; practically speaking, this sort of thing is likely to happen with most shiny speculars as well as with lights in the shot.

If I’d put the waveform monitor in Y mode, we’d see the greenscreen’s luma level along the left side hovering around 41% or so: the false-color green level defaults to 41% ± 2.5%.

Barney on a better-lit greenscreen

Now I’ve filled from the left with another Diva-lite 400. The side-to-side balance is just fine, though I still need to work on the greenscreen shadowing at the edges (it’s due to our subject being close enough to the screen that his diffuse shadows are falling on it. I’d move him forward, but he’d fall off the table. I’m also seeing some slight hotspotting at the upper corners due to the poor positioning of my lights, something the waveform monitor makes immediately apparent even if my eyes glossed over that half-stop difference. In microbudget production, this sort of sloppiness is regrettably common. Cine Meter makes it harder to overlook).

The blue is still rather toasty, but I’m using daylight tubes in the Kinos. Putting tungsten-balanced light on this backdrop might help. Even with the daylight tubes, the separation is tolerable; the VFX guy won’t have to work overtime on this key.

Cine Meter looking at greenscreen materials

A week later, with more money in the budget ($5.49), I try again: this time I get clever, and use Cine Meter to compare potential greenscreen material before I set up my “studio”. That middle material has much better separation (the left green is the same card I used before, though this time I’m lit with 2900K KinoFlos).

Looking at the new greenscreen

Immediately I see a cleaner and purer green, though my background illumination is kinda sloppy... again.

Balanced lighting, in YRGB mode

Cine Meter makes it easy to see when it’s evened up. I’ve put the waveform monitor in YRGB mode, so I can see the overall luma values as well as the color component levels.

False-color on the new greenscreen

If I turn on FalseColor, my levels are OK, but the false colors aren’t helping me much at their default settings.

Adjusting false-color for greenscreen lighting

The green “midtone” level defaults to 41%, but here I drag it to 75% to highlight the background lighting level.

Using false green to even out our screen

That makes it a lot easier to see when I have things better balanced.

Viewing YRGB in 1 line mode

To simplify things even further, I use 1 Line mode on the ’scope. By tilting Cine Meter up and down, I can scan that line across the entire vertical extent of the scene and see precisely whether my remaining imbalance is due to shadows at the top of the screen or the bottom.

This is a much better keying setup than I had before; the VFX guy can pull a key in his sleep. That’s $5.49 well spent... thanks to Cine Meter!

Big Pig and friend on a green cove

Big Pig and friend perch on a cove painted with Composite Components Digital Green, side-lit with a 10K fresnel, in this photo from Don Craig. (I have Cine Meter’s camera data overlay turned on, just for fun.)

There’s good separation between the green and the red and blue with this paint, so the VFX folks will be happy.

ChromaDuMonde® charts seen in Cine Meter screenshots used with kind permission of DSC Labs. DSC Labs is not responsible for any images viewed with Cine Meter, or how they appear in Cine Meter's pictures.

© 2013 Adam J. Wilt.  Last updated 2013.01.17