One of the most critical parts of aerial/drone survey is capturing the right images on field which is crucial for the photogrammetry process. Bad images lead to unusable outputs, which means you need to get on the field one more time repeating the same mission with better camera settings. Hence knowing the basics of camera parameters plays a very important role in capturing the right images.
Below image explains what is Aperture, Shutter Speed, ISO and its importance.
Let’s see how the images are affected in case any of the above settings goes wrong
- Slow Shutter Speed – If the shutter speed is slow it introduces ‘Motion Blur’. This makes the photogrammetry process difficult & also visual aesthetics is compromised. Arriving at an optimal value is very important depending on the light on a given day. In case the value falls below the optimal value we see motion blur which is shown in the below image.
- Wide Open Aperture – Wide open apertures are good when the light conditions are low. It compensates for the low light by allowing the light inside the aperture. But the disadvantage of this is the depth of field becomes shallow & the background will be out of focus which makes the photogrammetry process difficult to find key points. As you can see in the below image the rabbit (Foreground) is in focus but the background is out of focus.
- ISO – ISO is increased in low light scenario when both aperture & shutter speed cannot compensate for the low light. But the disadvantage of it is Noise/Grains will be introduced as shown in the below image.
The 3 camera modes and it’s advantage & disadvantages are explained below with respect to aerial mapping
- Auto – In the Auto mode both ‘Aperture & ‘Shutter Speed’ changes automatically by the sensor. Disadvantage of it is, in low light scenarios shutter speed will fall beyond the optimal value introducing motion blur. The following data was captured at 20kmph & as per the histogram the slowest shutter speed is at 1/60 of a second. Drone travelling at 20kmph & shutter speed falls which may have introduced motion blur.
- Manual – In the manual mode Aperture, Shutter Speed & ISO is controlled manually which makes the user busy in monitoring the camera settings & ignoring the line of sight which is very important.
- Aperture Priority – As the name says, here the aperture is set by the user manually which will remain constant throughout the flight. Only shutter speed varies as per the lighting conditions. Following histograms shows the disadvantage of this mode as the lowest value of shutter speed is at 1/160 of a second. Note:- ISO was set at 100 for this particular dataset
- Shutter Priority – Shutter priority is where the shutter is chosen by the user which will remain constant throughout the flight & aperture varies as per the lighting conditions. The data of the following histogram was captured on a cloudy day. It shows aperture varying from f/2.8 to f/9.
Had the pilot chosen to do the same flight in aperture priority mode with light being very low, the shutter speed would have dropped very low. Hence shutter priority was the right option.Note:- ISO was set at 100 for this particular dataset.
Comparing all 3 histograms, choosing ‘Shutter Priority’ will be a win-win option even in low light conditions as shallow depth of field is acceptable than blurry images. Hence ‘Shutter Priority’ is a safe option for aerial mapping.