Video distortion - best way to correct

jadebox said:
What I said is correct. Even if it weren't, there would be a loss in quality just from using less of the lens. It's like having a smaller lens.
I disagree with this statement, too. The center portion of the lens (almost any lens) is much sharper than the corners. In a fisheye lens, straight lines are also much less distorted.

Shooting with "less of the lens" can actually improve image quality.
 
jimre said:
jadebox said:
What I said is correct. Even if it weren't, there would be a loss in quality just from using less of the lens. It's like having a smaller lens.
I disagree with this statement, too. The center portion of the lens (almost any lens) is much sharper than the corners. In a fisheye lens, straight lines are also much less distorted.

Shooting with "less of the lens" can actually improve image quality.

If you could get just as good (or better) of an image from using a portion of the lens and a smaller sensor, photographers wouldn't invest so much money in larger lenses and larger format sensors and film.

While the center of the lens is usually of better quality (and the light is refracted less going through the center), when the Vision's camera is set to the 90 degree Field of View setting, it's capturing only about 1/4 as much light as it would using all of lens and sensor. Less light translates into more noise in the image.

Here's a video someone else made to demonstrate how the quality of the image drops when you reduce the field of view:

[youtube]http://www.youtube.com/watch?v=vCvpD4pu_Cw[/youtube]

You can see that the video gets noticeably more grainy when set to the 90 degree setting.

And here's the results of a test I just did. I sat the P2V on a shelf facing a white board. I recorded video at the full FOV and at the 90 degree FOV setting without changing the lighting or any other conditions. I scaled both videos by the same amount (500%). Here's what the result looks like. The 90 degree FOV image is on top. The full-FOV image is on the bottom.




The top half (90 degree FOV) shows considerably more noise.

If you're happy with the quality of the video when the camera is set to the 90 degree FOV, then use it. It's certainly easier to use the video directly than to do post-processing of the wide-angle shots to remove the fisheye effect. But, try recording in both modes to see the difference. Especially in lower light situations, it can be pretty obvious.

-- Roger
 
What's the deal with your crusade against 90° FOV?

And as a photographer, I can tell you that we don't invest in "larger lenses" for better picture quality (sensors, yes). We invest in *better* lenses - virtually all of which are sharpest in the middle.

You can pooh-pooh 90° FOV all you want, but this is still *light-years* better than cropping your 1080p video down to 700p in post, to get the same 90° field of view. That just looks horrible, no matter what you do.

I'll leave this discussion with the full video from my test:

https://vimeo.com/96341747

Pretty easy choice....
 
jadebox said:


The top half (90 degree FOV) shows considerably more noise.
The noise is certainly more noticeable on the top, because the bottom is so under-exposed you can't tell anything. This is a white board?
 
I hope it's ok to chip in here:

I have been testing both 90 and 140 FOV. I always notice however that the 90 version always looks 'washed out'. The colours never seem as vibrant and the contrast overall seems lower.

Is this something to do with where the metering or focusing sensors are located on the CCD.

Should I be adjusting settings in the app to compensate? Everything is set to auto.

I am new to this so I might not be using the right phrases.

Cheers,

A
 
Major_Defeat said:
I hope it's ok to chip in here:

I have been testing both 90 and 140 FOV. I always notice however that the 90 version always looks 'washed out'. The colours never seem as vibrant and the contrast overall seems lower.

Is this something to do with where the metering or focusing sensors are located on the CCD.

Should I be adjusting settings in the app to compensate? Everything is set to auto.

Cheers,

A
Since the camera is auto-exposure only, the exposure depends on what is in your picture. Your 90° video may look washed-out because it's over-exposed, compared with the 140° video - perhaps because the latter included more bright sky in the image (and therefore used a darker auto-exposure).

I had the opposite issue in the example video I posted above. My 90° video is exposed correctly for the rock wall, while the rock wall in the 140° video is a little bit under-exposed, probably due to the additional bright sky in the picture. I manually choose most of my camera settings, but ultimately it's still auto-exposure no matter what. My normal settings are ISO 100, -1.0EV exposure compensation, center-weighted exposure metering, sunny white balance. I have a circular polarizer filter on the lens. I find that skies are almost always over-exposed if I set the exposure compensation to 0, so I almost always use -1.0.

You could play with exposure metering, and try Spot metering to try and exposure properly for the center of your picture. But this will be hard to use accurately on a moving platform.
 
Thank you so much for the advice - I will try out those manual settings and see how I go.

I am wondering if the auto metering is occurring effectively outside of the frame I am seeing and in it (due to my settings) and because I tilt the camera in a different position it is indeed getting different exposure readings than what I expect.

The filter you are using - does that basically remove glare from water etc.?

I am going to have to do more flying to test this! ;)

Thanks again for the help.

A
 
jimre said:
What's the deal with your crusade against 90° FOV?

And as a photographer, I can tell you that we don't invest in "larger lenses" for better picture quality (sensors, yes). We invest in *better* lenses - virtually all of which are sharpest in the middle.

You can pooh-pooh 90° FOV all you want, but this is still *light-years* better than cropping your 1080p video down to 700p in post, to get the same 90° field of view. That just looks horrible, no matter what you do.

I'll leave this discussion with the full video from my test:

https://vimeo.com/96341747

Pretty easy choice....

My responses were in regards to reducing the fish eye effect, not about achieving a 90 degree field of view. I never suggested cropping a 1080p video down to 700p. I even suggested that using the narrow FOV if you're OK with the reduction in quality.

-- Roger
 
The noise is certainly more noticeable on the top, because the bottom is so under-exposed you can't tell anything. This is a white board?

Yes, as I explained, it was a white board. Both videos were recorded at the same light level. I purposefully performed the experiment in low light to accentuate the diference, but the narrow field if view will always suffer a reduction in quality of the full FOV.

-- Roger
 

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