FPV Latency

[annikk.exe]

Hi,

I have some questions about FPV latency, ie the time it takes between an image appearing in front of the camera, and that image being shown onscreen in front of your eyes.

What are the main components that affect the latency of FPV?  (From what I understand, the camera is generally the biggest latency bottleneck.  Is that true?)
Do the other components (video TX, RX, the screen/goggles, etc) have any bearing on latency?
Which camera has the lowest latency?
Why is latency a hard problem in FPV cameras in the first place?
Are there any low-latency CCD cameras with WDR etc, that are also 800 TVL or greater?
Are there any documented mods to improve the latency of an FPV camera?
Are digital transmission solutions (eg Lightbridge) better or worse than regular analog, in terms of latency?

[Chippercheese]

Hi,

I have some questions about FPV latency, ie the time it takes between an image appearing in front of the camera, and that image being shown onscreen in front of your eyes.

What are the main components that affect the latency of FPV?  (From what I understand, the camera is generally the biggest latency bottleneck.  Is that true?)
Do the other components (video TX, RX, the screen/goggles, etc) have any bearing on latency?
Which camera has the lowest latency?
Why is latency a hard problem in FPV cameras in the first place?
Are there any low-latency CCD cameras with WDR etc, that are also 800 TVL or greater?
Are there any documented mods to improve the latency of an FPV camera?
Are digital transmission solutions (eg Lightbridge) better or worse than regular analog, in terms of latency?

In my experience, you';ll experience latency with any digital camera that processes the image (gopro, mobius, fatshark pilothd for example)

Analogue cameras (like your bog standard $10 CMOS board cam) will be pretty much real-time, at least in terms of human perception. Radio gear shouldn';t provide any latency, unless you';re flying thousands of miles away, as it carries the bare signal over RF with no added processing/jiggery-poker.

I';ve yet to see the whole lightbridge/HD streaming thing in action myself.

[annikk.exe]

I watched this youtube video and it seems to show that most cameras are quite slow (100ms+) but there is one 600TVL camera that is much faster.  Unlike most other latency testing videos, the guy is actually using a decent methodology to figure out the latency of the cameras.  It really shows the difference.

If anyone has an FPV camera not featured in the video, and is able to do a latency test with the same method used in the video, that would be very cool and interesting to see some other comparisons.. :>

[Revs]

I have several different board cams and non have any noticeable latency. 800TVL Emax, 700TVL Sony SuperHAD and 600TVL Sony SuperHAD.

As opposed to the GoPro, Mobius, etc that all have enough latency to make them unsuitable for FPV imo.

[dirtyharry]

Latency

Sonny 600tvl = 0.02 seconds
effio-v 800tvl 0.1 seconds

Mobius 720p= 0.063s
mobius 1080p= 0.093s

Is latency really an issue or just a talking point ,  I use 600tvl superhad sonny  as their cheap + give the best all round performance for me. You can only ask a 5.8ghz video transmission to carry so much info , so above 600tvl theres going to be some processing and for FPV its not a win- win situation.

[kilby]

If you stop the video at any point you see something like 0.02 second discrepancy between the board camera and the output.

Considering 0.02 works out at 1/50th of a second (the speed of a PAL frame) it';s not overly surprising.

There is a difference between how CCD & CMOS pull data out of the sensor but it';s negligible (counts for the curved props in videos though)

There have been complaints with the Effio CCD devices but turning off the 3d noise filtering solves most of the issues (as does the later revisions), also these complaints have been mostly from armchair pilots and a lot of the well known proximity flyers have absolutely no issues with latency on them

[annikk.exe]

Ah, so that';s why some quadcopter videos feature curvy propellers.. :>  I guess that';s because it doesn';t capture all of the pixels at once, but does them top-to-bottom or something?

Is latency really an issue or just a talking point

To be honest I don';t know how much of an issue it is, since I';ve never flown FPV before.
I plan to, though.  Coming from a background in twitch computer gaming, where latency is very important, I figured a the same would be true for FPV.  It would make sense... you only get a certain amount of time to see the tree branch coming in, and dodge it.  If the latency is larger, that';s going to impact your total reaction time.

On the other hand, better resolution means the branch is visible from further away.

I';ve heard most of the FPV racers tend to use the Sony 600TVL camera that you mentioned because it has the lowest latency.

[kilby]

Ah, so that';s why some quadcopter videos feature curvy propellers.. :>  I guess that';s because it doesn';t capture all of the pixels at once, but does them top-to-bottom or something?

The pixels are captured by scanning the sensor rows, and the time taken to read each row.

CMOS cameras are often written off by people, but the image is decent an they';re usually better than CCD at light/dark (or vice versa) transitions, they';re also supposed to cope better in high contrast situations.

Essentially the less processing (noise reduction etc) the camera has to do the more suitable it is for FPV

[annikk.exe]

CMOS cameras are often written off by people, but the image is decent an they';re usually better than CCD at light/dark (or vice versa) transitions, they';re also supposed to cope better in high contrast situations.

I thought CCD was better for light/dark transititions?

Essentially the less processing (noise reduction etc) the camera has to do the more suitable it is for FPV

Ah right, that';s quite interesting..  Could it be that the larger TVL count cameras simply have more post-processing features turned on?
I guess my ultimate goal here is to have Pal-Frame latency with an 800TVL camera.  That way I  can justify buying the Dominator HD.. :P

[Revs]

CCD';s are generally more sensitive but colours can be flat and contrast too high. CMOS sensors have more colour definition and give a more natural image.

How good the light/dark transitions are is generally down to firmware as that is what controls the auto exposure.