Does CPL affect video quality?

[D23]

Hi guys,
I've brough the CPL home and it works great during daytime. 80% of reflectioin has gone.
However it's not that good during night time especially in low light area. Kind of noise and most of the time I can't even read the number plate of other vehicles.
It's 40usd cpl and I expected more than that
Does everyone has experienced the same problem?
How about the SG9665GC V3 which come with CPL?
This is the link:

E/V set to 0
Contrast set to 0
firmware V30
Windshield is crystal clear

 

[jokiin]

The CPL filter is about removing reflections, this can also be beneficial at night if you have other interior lights etc that reflect, it will increase the effective f stop of the lens so more noise is expected, it won't improve the ability to read number plates in low light situations though, there's a thread here that @niko started previously that has demos in all types of lighting situations with and without the CPL filter so you can know what results to expect

 

[thancam]

Yes, it does. You cant refine amoun of light though filter and hoping: image will still the same. That's imposible.
What kind of CPL filter will effect to quality of image too. With CPL filter of SG, it's one of the best in dashcam market.

 

[niko]

Here is complete day and night test with / without CPL

https://dashcamtalk.com/forum/threa...ns-filter-for-street-guardian-sg9665gc.14256/

 

[jokiin]

Here is complete day and night test with / without CPL

https://dashcamtalk.com/forum/threa...ns-filter-for-street-guardian-sg9665gc.14256/

Thanks, I would normally post a link but I'm on mobile at the moment and couldn't find it easily

 

[Nigel]

Does CPL affect video quality?

Of course it affects video quality, the only reason to have a CPL is to improve video quality by removing the reflections.

Removing the reflections makes it easier to read the plates etc. It also gives the video compression an easier time since it takes a lot more bitrate to encode two images superimposed on each other with one moving and one not moving. Since we use fixed bitrates it actually means that the bitrate freed up by not having to encode the reflections is used for more important things.

The negative is that it removes half the light, or at least a good CPL will remove half the light, and the auto exposure then has to double the shutter speed which doubles the motion blur, so in dark conditions the extra motion blur can reduce readability of plates. Also, at times it will increase the ISO setting by 1 instead of doubling the shutter speed, and that will increase the noise which may be noticeable at night.

 

[D23]

... but I did expect better result (

 

[Feitelijk]

You have it. Daytime is much improved, but...
A CPL is removing about 50% of the light. Which means that the cam will increase sensitivity of exposuretime in low light contitions.
This in turn will add noise in the first case and motionblur in the second.

 

[D23]

So I can remove the CPL if I want better quality during nightime.
But what happens to the SG9665 V3 with CPL already in it, Can we remove CPL of the V3 model for better quality?

 

[jokiin]

CPL is included with the V3, it clips on though and can be removed

 

[Feitelijk]

So I can remove the CPL if I want better quality during nightime.

Yes!

 

[thancam]

So I can remove the CPL if I want better quality during nightime.
But what happens to the SG9665 V3 with CPL already in it, Can we remove CPL of the V3 model for better quality?

if you have a white dashboard, then you will improve quality of image with CPL. If you have a dark dashboard, you wont need CPL.
i have some kind of dashcams with CPL. All of them then i put CPL, image become so darker that i have to increase EV from 1/3 to 1. With SG, you dont need to.

 

[daniel_bel]

Not only the dashboard, in my case the most reflections come from my SatNav devices screen reflecting.
And one has a shiny metal-grey backside, a real star it "takes the light maaaarvelously"