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underwater_videography_with_gopro [2025/05/01 19:47] – qlyoungunderwater_videography_with_gopro [2025/05/07 22:44] (current) – include percent sign qlyoung
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 I(z) = I₀ ​e⁻ᵏᶻ I(z) = I₀ ​e⁻ᵏᶻ
  
-Where *I₀​* is the initial light intensity (at the surface), *I(z)* is the intensity at depth, *z*, and *k* is the absorption coefficient that varies depending on the medium characteristics (for water, things like clarity and particle content).+where *I₀​* is the initial light intensity (at the surface), *I(z)* is the intensity at depth, *z*, and *k* is the absorption coefficient that varies depending on the medium characteristics (for water, things like clarity and particle content).
  
-For air *k* is around 0.0001. For seawater *k* is more like 0.1. That gives us roughly the following:+For air *k* is around 0.0001. For seawater *k* is more like 0.05. That gives us roughly the following:
  
-| Depth (m) | Light Intensity (%) | +| Depth (m) | Depth (ft) | Light Intensity (%) | 
-|-----------|---------------------| +|------------|------------|---------------------| 
-| 0         | 100.00%             | +| 0          | 0          | 100%                | 
-| 5         | 60.65%              | +| 5          | 15         | 78%                 | 
-| 10        | 36.79%              | +| 10         | 35         | 61%                 | 
-| 15        | 22.31%              | +| 15         | 50         | 47%                 | 
-| 20        | 13.53%              | +| 20         | 65         | 37%                 | 
-| 30        | 4.98%               | +| 25         | 80         | 29%                 | 
-| 40        | 1.83%               |+| 30         | 100        | 22%                 | 
 +| 35         | 115        | 17%                 | 
 +| 40         | 130        | 14%                 | 
 +| 45         | 150        | 11%                 | 
 +| 50         | 165        | 8%                  | 
 + 
 + 
 + 
 +It's much more complicated than this - absorption is wavelength dependent, seawater is not uniform, there are scattering effects, etc - but this is a decent approximation for this discussion.
  
 The upshot is that the diving environment is low light as far as cameras are concerned. This is why underwater photographers have kit that looks like this: The upshot is that the diving environment is low light as far as cameras are concerned. This is why underwater photographers have kit that looks like this:
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 ## Sensor size ## Sensor size
  
-A full frame camera sensor is ~43mm on the diagonal. The Hero 11 has a 1/1.9" sensor size, roughly 13mm diagonal. That is over 3 times smaller.+Generally speaking the larger the sensor, the more light it can collect and the better its dynamic range. Smaller sensors struggle more in low light. 
 + 
 +To put in perspective how challenging it can be to use an action cam underwater: 
 + 
 +A full frame camera sensor is roughly 36x24mm for an area of 864mm^2. The Hero 11 sensor is 6.74x5.05mm for a sensor area of 34.04 mm^2. That is ~25x smaller than full frame.
  
-Wasn't sure where else to put this information.+If you are wondering why 6.74x5.05mm does not correspond to the 1/1.9" figure published by GoPro, that is because that figure is in {{wp>optical format}}.
  
 ## Color ## Color
  
-Water is blue because it preferentially absorbs wavelengths of light other than blue. The deeper you get the more light is absorbed and the bluer the scene.+Water is blue because it preferentially absorbs wavelengths of light other than blue. The deeper you are the further light has to travel through water, the more red light is absorbed and the bluer the scene.
  
 {{:absorption_coefficient_of_water.png?600|}} {{:absorption_coefficient_of_water.png?600|}}
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  -  Spectrum is constantly varying with depth and other things, on the balance I've found I get the best result allowing the camera to handle it  -  Spectrum is constantly varying with depth and other things, on the balance I've found I get the best result allowing the camera to handle it
 - Wide lens - Wide lens
- - "Wide" is the native lens. "Narrow" crops it, "Hyperview" and "Superview" convert 8:7 and 4:3 video respectively to 16:9 using an in-camera distortion mapping. I prefer an output with minimal in-camera corrections so I use "Wide". If you want 16:9 you should select that as an export option in Gyroflow instead of in the camera; that way Gyroflow benefits from the additional buffer space to perform corrections and then crops at the end. + - "Wide" is the native lens. "Narrow" crops it, "Hyperview" and "Superview" convert 8:7 and 4:3 video respectively to 16:9 using an in-camera distortion mapping. I prefer an output with minimal in-camera corrections so I use "Wide". 
- - This also helps Gyroflow; while it is capable of stabilizing Hyper/SuperView footage, that feature uses a reverse-engineered distortion matrix to undo the distortion. There's no point in using Hyperview, undoing it, then redoing it in export.+ - Notably, if you are using Gyroflow and want 16:9 you should shoot in 8:7 and select 16:9 as an export option in Gyroflow instead of in the camera; that way Gyroflow benefits from the additional buffer space to perform corrections and then crops at the end. Gyroflow can stabilize Hyper/SuperView footage, but in order to do so it has to undo the Hyperview distortion first using a reverse-engineered distortion matrix and then re-apply it, so you may as well shoot without it to begin with
  
 {{::hyperview-etc.jpg|}} {{::hyperview-etc.jpg|}}
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  - If I want to shoot 60fps for some reason then I drop the resolution to 4k in order to keep the 8:7 aspect ratio. If you want the absolute highest resolution, you can drop to 16:9 which unlocks 5.3k60. Personally I prefer working in a consistent aspect ratio and think 4k subsampling looks good enough especially at high framerates.  - If I want to shoot 60fps for some reason then I drop the resolution to 4k in order to keep the 8:7 aspect ratio. If you want the absolute highest resolution, you can drop to 16:9 which unlocks 5.3k60. Personally I prefer working in a consistent aspect ratio and think 4k subsampling looks good enough especially at high framerates.
 - Hypersmooth off - Hypersmooth off
- - I prefer to stabilize in post with [Gyroflow](https://gyroflow.xyz/). I think the result is better and it grants far more control over the stabilization parameters. See the section on stabilization for additional reasons.+ - Water or not, I prefer to stabilize in post with [Gyroflow](https://gyroflow.xyz/). The result is better and it allows more control over the stabilization parameters 
 + - Hypersmooth is calibrated for the refractive index of air and is only 70% effective in water; Gyroflow accounts for water if configured correctly 
 + - See the section on stabilization for more detail
 - Bitrate high - Bitrate high
- - Of course+ - Higher bitrate generally equals better quality video
 - 10-bit on - 10-bit on
- - I paid good money for those bits+ - More {{wp>Color depth|bit depth}} allows capturing finer grained color differences, which looks significantly better 
 + - Greater bit depth also reduces {{wp>Color banding}} which is often a problem in underwater footage, which tends to have diffuse color gradients as the backdrop
 - Shutter auto - Shutter auto
  - The camera knows best  - The camera knows best
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 I find it works best with a 3/4" or 1" bolt snap attached like this: I find it works best with a 3/4" or 1" bolt snap attached like this:
  
-{{::25-05-01_12-56-50_8320.jpg?600|}}+{{:rot.jpg?400|}}
  
 During shooting I just hold the camera itself. I have tried handles, including the official GoPro dive handle. I don't notice any improvement in footage and it is bulky. During shooting I just hold the camera itself. I have tried handles, including the official GoPro dive handle. I don't notice any improvement in footage and it is bulky.
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underwater_videography_with_gopro.1746128841.txt.gz · Last modified: 2025/05/01 19:47 by qlyoung
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