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When is digital zoom the same as optical?

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When shooting video at a lower resolution than the sensor.

Consider the Air 2S. 20MP sensor. It has a resolution of 5472×3648, 3:2 aspect ratio. At 16:9 the sensor is cropped vertically to 5472×3078.

Stills will always be shot at the full resolution, so digital "zoom" would just crop the sensor output, and blow up the pixels to fill 5472×3648. Nothing gained.

With video, however, there are several target resolutions that you may be capturing where sensor resolution is actually thrown away in processing the video stream, and can be used for lossless digital zoom.

Suppose your project requires 1080p (FHD). You've set the camera for 1080/60. Here's what's happening: Each frame is captured at 5472×3078. The GPU downscales this to 1920×1080, then feeds it to the video compression process.

Now, were you to zoom this in in post, you would be losing resolution. Let's say you want to focus in on a building, zooming 4x. This would simply take a 960×540 section and blow up each pixel to cover 4 – and it would look awful.

However, perform this 4x zoom while capturing the video, and the building will be full 1080p resolution every pixel containing detail. This is because nothing gets enlarged. Instead, the area of the sensor being used for the image gets cropped, and the downscaling by the GPU reduces proportionally. All the way to 4x zoom where the center ¼ of the sensor is cropped, and is ~1920×1080, full FHD resolution.

Again, no good for still photos. There is no option (or reason) to capture stills in anything but full resolution. Any cropping can be done in post. It's no surprise photographers are pretty sour on digital zoom in general.

Yet for video it can be very useful depending on the target output. On several models, certain features can only be used in lower resolution, like 120fps, making digital zoom a viable and useful feature in these circumstances.

On the Air 2S, here's the digital zoom "headroom" available without detail loss for the different shooting modes:

FHD: 8x (5472/1920)²
2.7K: 4x
UHD: 2x
5.4k: none

Mini3P:
FHD: 4x (4032/1920)²
2.7k: 2x
UHD: 1.1 i.e. 10%, but the drone doesn't support any zooming in 4k
 
You will still find quality loss and quality mismatch, as video downsampled from a higher native resolution will look better than the one captured from a sensor crop.

The way to go is always shoot at max resolution of the sensor, then crop in postproduction. You should also avoid any render or process being done by the drone/camera itself, as their computing power is a crap and you'll lose quality.

So capture at max quality, do the postpro on a computer.

PS: That if you want the max image quality, for internet reels and YT content it really doesn't matter as it gets compressed to the ground and watched in a mobile phone screen.
 
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Zooming in post processing works very well if you don’t zoom beyond the native resolution of the capture.
 
When shooting video at a lower resolution than the sensor.

Consider the Air 2S. 20MP sensor. It has a resolution of 5472×3648, 3:2 aspect ratio. At 16:9 the sensor is cropped vertically to 5472×3078.

Stills will always be shot at the full resolution, so digital "zoom" would just crop the sensor output, and blow up the pixels to fill 5472×3648. Nothing gained.

With video, however, there are several target resolutions that you may be capturing where sensor resolution is actually thrown away in processing the video stream, and can be used for lossless digital zoom.

Suppose your project requires 1080p (FHD). You've set the camera for 1080/60. Here's what's happening: Each frame is captured at 5472×3078. The GPU downscales this to 1920×1080, then feeds it to the video compression process.

Now, were you to zoom this in in post, you would be losing resolution. Let's say you want to focus in on a building, zooming 4x. This would simply take a 960×540 section and blow up each pixel to cover 4 – and it would look awful.

However, perform this 4x zoom while capturing the video, and the building will be full 1080p resolution every pixel containing detail. This is because nothing gets enlarged. Instead, the area of the sensor being used for the image gets cropped, and the downscaling by the GPU reduces proportionally. All the way to 4x zoom where the center ¼ of the sensor is cropped, and is ~1920×1080, full FHD resolution.

Again, no good for still photos. There is no option (or reason) to capture stills in anything but full resolution. Any cropping can be done in post. It's no surprise photographers are pretty sour on digital zoom in general.

Yet for video it can be very useful depending on the target output. On several models, certain features can only be used in lower resolution, like 120fps, making digital zoom a viable and useful feature in these circumstances.

On the Air 2S, here's the digital zoom "headroom" available without detail loss for the different shooting modes:

FHD: 8x (5472/1920)²
2.7K: 4x
UHD: 2x
5.4k: none

Mini3P:
FHD: 4x (4032/1920)²
2.7k: 2x
UHD: 1.1 i.e. 10%, but the drone doesn't support any zooming in 4k
Never , optical zoom or nothing, cheers Len
 
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