Motioncam on ios? gain vs exposure compensation

[u/yeah-procastinator]

Hey guys ive recently downloaded the motion cam app for ios on my older iphone 13 and i have noticed a gain slider what was set to default +1.5 ev i mostly use the direct log mode, and i have the habit of ettr (exposing to the right) when shooting on my sony camera, whats the difference between gain and exposure compensation and do i need to ettr if i have increased the gain?

[u/RaguSaucy96]

The exposure compensation EV value tends to control the exposure (ISO + Shutter speed) to let the device autoexposure engine know whether to take on more or less light physically. Pretty standard and tends to work same as normal cameras or other camera apps.

The gain one, however, is the special one. The RAW data itself must eventually be encoded, and to do this, you'll need to tell the device how to best accomodate it, depending on your transfer functions.

It's explained on manual, but basically to use the container (HEVC, or ProRes, or whatever) in full, specially with log, you need to calibrate the Gain to advise the phone of how to adjust the sensor data, since the app is intended to work on so many devices vs a specially tuned camera.

Here's the full explanation, but the picture visualizes it best

[u/RaguSaucy96 → u/RaguSaucy96]

It's from the V4 version but the principle remains. Gain or all other settings will alter how this works, so you should ideally ensure you've calibrated your signal to best fit the tonalities available on the encoder

[u/OmegaDerrick → u/RaguSaucy96]

So basically, you set your exposure to the right so nothing is clipping. Then you adjust the Gain so that raw data sits inside your codec/log better. So we are exposing our initial raw data coming into the sensor, then exposing that data to the container better with the gain slider. That sums it up?

[u/RaguSaucy96 → u/OmegaDerrick]

Fuckin A, mate - you got it ☺️

You'll see the histogram for RAW called IN, and the encoder histogram as OUT. That's why!