Evo II Pro 6K crop factor

[Greg]

I’ve discovered that the 6K camera crops in 4K at 40, 50 and 60 FPS.
all resolutions at 30fps or less are not cropped.
however 1080 / 120fps is not cropped.
not something mentioned anywhere....

 

[Jagerbomb52]

I believe one of the reviewers had mentioned that but I cannot remember which one. Autel has a lot of catching up to do with updating their web site with true specs and tutorial videos for the EVO II. I'm sure it will all come in time as they are a small group.

 

[Ken Ramsley]

It basically comes down to the problem of down-sampling and the computing power to accomplish this. If you have a native 8K camera sensor and down-sample to 4K, it is as simple as grouping a 4-square of pixels and averaging the data. In a native 6K array, you could do the same thing to produce a '3K' image -- but producing a 4K image requires a few more steps to work out the average -- steps the camera can complete given more time (30 fps vrs 50 or 60 fps). If 50 or 60 fps 4K from a 6K array is essential, the only solution is cropping the image to an exact 4K pixel array (which is what Autel does). FYI, 1080p can directly down-sample a 9-square of native 6K pixels -- allowing faster fps, and where the overall data rate of 1080p is low, they can bump the framerate to 120 fps. Hope this makes sense.

 

[tvwxman]

Ken, thanks for your insight, yes that made sense! Follow-up question: I realize stepping up from 30fps to 60fps reduces the exposure due to the increased shutter speed, but when sacrificing the 6K array for the 4K array am I assuming correctly that you are also sacrificing the light gathering ability of the 6K array using the full 1" sensor and the additional pixels which would have otherwise been averaged?

 

[Ken Ramsley]

Ken, thanks for your insight, yes that made sense! Follow-up question: I realize stepping up from 30fps to 60fps reduces the exposure due to the increased shutter speed, but when sacrificing the 6K array for the 4K array am I assuming correctly that you are also sacrificing the light gathering ability of the 6K array using the full 1" sensor and the additional pixels which would have otherwise been averaged?

As long as the cropping process does not downsample (which would add data from several pixels and speed up exposure times), the camera's exposure performance will work the same no matter how it is cropped.

In fact, when Autel crops a 6K image sensor frame to 4K, it is simply snipping out the central 4k of pixels (like running 16mm film through a 35mm camera ...if that were possible). Where nothing changes optically and where you are only snipping a piece of the image, exposure settings (f/stop and shutter speed) are the same.

The quality downside is a matter of magnification. Cropping a 4k image out of a 6K sensor records only ~50% of your 1-inch sensor surface area, and you wind up magnifying that smaller image to fit your post-production display screen.

For lack of a better way of summarizing this, the way Autel crops 4K cropped from a 6K sensor is nothing more than a 'digital zoom' -- and most thoughts on the matter of digital zooming generally apply.

 

[tvwxman]

Wow Ken you need to teach a course, really great information thanks so much this was driving me crazy wondering about all this, but never asked on this forum since I figured everyone was more interested in flying than getting into the weeds on image sensors!! Thank you again sir, really appreciate it!

 

[Ken Ramsley]

My Dad was a founding member of the American Optical Society, and I suppose the apple did not roll very far from the tree. Years ago, I built hobby telescopes (up to 12-inches in aperture) including the fabrication and testing of my own telescope mirrors. After that, I designed cameras for spacecraft, and soon after that, I taught spacecraft engineering. Most recently, I became a planetary scientist where I sometimes predict the optical performance of space-probe cameras to suggest what we might and might not detect from space -- and all of that is just the tip of the iceberg of my interests in optics and cameras.

 

[tvwxman]

Well that is indeed a fascinating and deep background in optics! And with that in mind, please don't leave this forum, I'm sure I (we) will have more questions!!

 

[dbeaty]

I had the exact series of questions Ken. Thanks for explaining what I was seeing in the crop factor. Now I am wondering what is a good resolution and frame rate to shoot in if I don't need HFR but also want to use the maximum performance of the sensor?

 

[herein2021]

I had the exact series of questions Ken. Thanks for explaining what I was seeing in the crop factor. Now I am wondering what is a good resolution and frame rate to shoot in if I don't need HFR but also want to use the maximum performance of the sensor?

I personally have settled upon 4K30FPS to get the maximum performance from the sensor. At 4K30FPS you get 4:2:0 10 bit color and no crop. If your WB and exposure are dialed in perfectly but you want a little latitude in post to crop and zoom then 6K 8bit 4;2:0 isn't a bad alternative. If you plan on speed ramping or think you might need to slow the footage later then 4K60FPS is the best option.

Like with anything, there is no one size fits all; I pick my framerate and resolution based on more than just 10bit vs. 8bit.