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underwater_videography_with_gopro [2025/05/01 17:38] – a qlyoungunderwater_videography_with_gopro [2025/05/07 22:44] (current) – include percent sign qlyoung
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 # underwater videography with gopro # underwater videography with gopro
  
-This will describe what I do to get decent results out of a GoPro when shooting underwater.+What I do to get decent results out of a GoPro when shooting underwater.
  
 # Light # Light
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 Cameras are light gathering devices and perform better the more light is available, all else being equal. How much light is available in the water? Cameras are light gathering devices and perform better the more light is available, all else being equal. How much light is available in the water?
  
-Water absorbs light fairly rapidly compared to air. Attenuation of light in a medium is described by the [Beer-Lambert law](https://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law); in short, surface light decreases as a function of depth per+Attenuation of light in a medium is described by the [Beer-Lambert law](https://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law). In terms of water, light intensity decreases as a function of depth per
  
-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 water's characteristics (such as 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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 Notice that the camera itself is the smallest part of the whole setup, most of the bulk is dedicated to lighting to add back in light absorbed by the water. Notice that the camera itself is the smallest part of the whole setup, most of the bulk is dedicated to lighting to add back in light absorbed by the water.
 +
 +## Sensor size
 +
 +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.
 +
 +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|}}
  
-The only way to truly fix this is to add the missing red wavelengths back in with external light.+The only way to truly compensate for this is to add the missing red wavelengths back in with external light.
  
-The other thing you can do is adjust the white balance of the sensor to make it more sensitive to red wavelengths. Every sensor pixel has red, green and blue subpixels. The values from these pixels are combined to produce a single pixel color. Adjusting white balance biases the color information collected by subpixels to include more of the red channel.+In camera you can adjust the white balance of the sensor to make it more sensitive to red wavelengths. Every sensor pixel has red, green and blue subpixels. The values from these pixels are combined to produce a single pixel color. Adjusting white balance biases the color information collected by subpixels to include more of the red channel. More on this in the Settings section.
  
 ### Filters ### Filters
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 ## Framerate ## Framerate
  
-Explanation of how a camera sensor works is out of scope for this discussion but roughly speaking:+Slower framerate allows for longer exposure times. Longer exposure allows more light and better picture, all else being equal. My advice is to bias towards lower framerates in water to give the camera more breathing room.
  
-- Larger sensors are less noisy all else being equal +Diving is a slow sport, so 30fps is usually plenty. Personally I find it looks better / more cinematic as well. Fast, active subjects such as bait balls might benefit from 60fps. As a rule of thumb, start at 30 unless you plan to shoot something fast or want the action cam look, then consider bumping to 60 and potentially increasing ISO max to allow the camera a little more flexibility.
-- Dynamic range scales with sensor size - especially in highlights +
- +
-Consider that you need that lighting rig to get good pictures out of full size cameras with relatively large sensors. 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. Now consider in that we are shooting video, which means exposure times are at most to the video framerate - usually 1/60 or 1/30. +
- +
-Slower framerate allows for longer exposure times, more light and better picture, all else being equal. My advice is to bias towards lower framerates in water to give the camera more breathing room.  +
- +
-Diving is a slow sport, so 30fps is usually plenty. Personally I find it looks better / more cinematic as well. Fast, active subjects such as bait balls might benefit from 60fps. Basically start at 30 and if you think you might need it change to 60.+
  
 ## ISO ## ISO
  
-So far we have established that: +In digital cameras ISO adjusts the electrical sensitivity of the sensor elements to incoming light. The tradeoff is that increased sensitivity results in lower SNR - i.e. higher ISO produces more noise. Fortunately denoising is very good these days, so if you are willing to denoise in post, you can get away with relatively high ISO.
- +
-- All diving footage is low light footage +
-- Small sensor size is working against us +
- +
-A useful weapon against these is ISO. In digital cameras it adjusts the electrical sensitivity of the sensor elements to incoming light. The tradeoff is that increased sensitivity results in lower SNR - i.e. higher ISO produces more noise. Fortunately denoising is very good these days, so if you are willing to denoise in post, you can get away with relatively high ISO.+
  
 I usually limit to 1600. I usually limit to 1600.
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 - Natural color - Natural color
  - `Flat` or a custom log curve in theory grant you more flexibility for color correction in post. However, after editing underwater LOG footage I realized that I do not care and that natural looks completely fine to my eye, so I don't use it anymore.  - `Flat` or a custom log curve in theory grant you more flexibility for color correction in post. However, after editing underwater LOG footage I realized that I do not care and that natural looks completely fine to my eye, so I don't use it anymore.
 +- White balance auto
 + -  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 have a Hero 11 and haven't used either of these settings so I can't speak to how well they work. I have a Hero 11 and haven't used either of these settings so I can't speak to how well they work.
  
-# Diving Praxis+# Praxis
  
 ## Case ## Case
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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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 ## Stabilization ## Stabilization
- 
-### Overview 
  
 Image stabilization is used to turn shaky handheld camera footage into nice smooth footage. Optical image stabilization, typically found in full size cameras, does this with motors that physically move the lens to cancel out shake and vibration. Image stabilization is used to turn shaky handheld camera footage into nice smooth footage. Optical image stabilization, typically found in full size cameras, does this with motors that physically move the lens to cancel out shake and vibration.
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underwater_videography_with_gopro.1746121093.txt.gz · Last modified: 2025/05/01 17:38 by qlyoung
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