Quality of Video 0826/0805

garrycol

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I have a 0816 watching out the front of the car and a 0805 looking out the back - both are set to 2304x1295 resolution as I figured that in an incident where I needed to freeze frames to view registration numbers with the highest resolution I would be able to do it when the target was some distance away.

Today I had an incident where two cars up in front of me had a coming together and one took off passing me going the other way - tracked the car as it came towards me then as it went away - all caught on the dash cam but neither at the front or the rear was I able to read the number plate.

From the front - the silver car about 20' away zooming in does not help

Frame F6.jpg

From the rear - zooming in does not help reading the number plate of the silver car but the blue car is easily read. The camera was looking straight at the blue car but the silver one is a fair way to the left.
Frame 8.jpg

This is the first time I have really needed to use the dash cam for an accident and while the general vision is moving vision is available and OK, it is not good enough to read the number plate of the silver car even when the movie and still pics are zoomed in. So it has failed my needs.

Replicator works Ok but resolution is lost when you zoom in - also tried a few other apps without success. Even tried the old Apple Quick Time that will view the movie in native resolution of 2304X1295 but the view is 4x the size of the computer screen but you cannot move the section of the image that you want onto the screen.

Also - resolution would seem to be best what the camera is looking at like the blue car but not so good at its extremities which I guess it understandable.

Is there any other software I could use to get a better look at the number plate. As it is the two Minicams have failed their first real tests where specific identification of a number plate was needed. Maybe I should just rig up my Samsung phone as I am sure it would have got the number plate.

As far as dash cams are concerned maybe I need to upgrade to something that has similar resolution but will give better real life results - open to suggestions.

Thanks

Garry
 

Mozzie

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Why don't you put the raw videos (trimmed) on the cloud (eg. mega, dropbox, googledrive, etc) and let someone here use there best tools to read the plate for you.
 
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garrycol

garrycol

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have you tried the 2560 x 1080 option?
Hmm no - will that make better? - I have no idea as I just thought that the higher resolution the better it would be

Why don't you put the raw videos (trimmed) on the cloud (eg. mega, dropbox, googledrive, etc) and let someone here use there best tools to read the plate for you.
Sorry I have no idea about any of that - I just use the Dash Cam and was expecting it to be able to display numberplates in frame capture. I have to say the quality of video etc does not match the resolution so I assume the lens in these Mini Cams is pretty ordinary.
 

jokiin

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Hmm no - will that make better? - I have no idea as I just thought that the higher resolution the better it would be
if yours has that option the general consensus is that it was the better end result of the available options
 

Mozzie

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Sorry I have no idea about any of that - I just use the Dash Cam and was expecting it to be able to display numberplates in frame capture. I have to say the quality of video etc does not match the resolution so I assume the lens in these Mini Cams is pretty ordinary.
I was suggesting that if you upload your video somewhere that someone may assist to look at it better. There are different viewers that produce better results and may be able to identify the plate.
 
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garrycol

garrycol

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Thanks - changed the resolution as recommended and I will test when I head out next.
 
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garrycol

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Thanks for the comments - changed the resolution but number plates are still readable - I think it is the lens in the dash cam and the glass in the windscreen. When looking straight ahead directly through the windscreen, the camera does alright however at a wider angle where the light travels at an angle through the windscreen glass and comes in at an angle through the lens things like number plates are not readable.

The mini dashcam series while highly regarded are relatively cheap and I guess this shows up in some areas.

Cheers

Garry
 

c4rc4m

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My take on this from my limited knowledge of cameras - 3 factors in my opinion:

1. Many cheaper lenses as often fitted to dashcams often fall off in performance at the edges (there are reasons why eg Canon pro camera lenses cost £1,000K+ per lens)

2. Window glass - get more reflection and aberrations from this when looking at an acute angle

3. The car behind is travelling in the same direction as you and therefore the relative speed difference between your vehicle and that is near zero. The car on the other side of the road is coming towards you so the speed difference is the sum of your 2 speeds eg at 30mph, 30 + 30 mph = 60 mph.

Now you're probably wondering what the significance of the relative speed is. Well it's to do with the rate of change of the data the camera is recording. The car behind, because it's hardly moving relative to yours, hardly changes from frame to frame, so needs very little compression (I understand many compression systems work by comparing the current frame with the previous frame and just recoding the data change). The more change and data to be recorded, the higher the compression and the more data is discarded resulting in more inaccuracy in the uncompressed picture. That's why when you watch people's dashcam videos with trees at the side of the road, often the car in front and road are sharp, but all the trees at the side are full of artefacts and blur = a lot of data in the leaves and a lot of change from frame to frame in that data = very high compression needed, and a lot of subsequent data loss.

There's also little blur frame to frame, as the car behind is either moving straight away or closer with any speed change, so any change in position during the exposure time translates to a slight zoom in or out = a slight fattening of the letters. The car coming the other way on the other hand, is moving it's position a lot from frame to frame (closing speed around 60mph at 30mph each), and so needs a lot more compression as the data change in this area high as it's position is changing rapidly, and compression = artefacts = a less clear picture. The plate is also moving a lot relative to your position as it's not coming straight at you but from an ever changing sidewards angle and so any distance travelled during the exposure time per frame translates much more to blur as the sides of the letter blur sideways during the exposure due to the fact it's travelling sideways across the frame relative to your position. This tends to make the letters blend together and become unreadable. So, in summary, it's harder for the camera to deal with the faster sideways (in the frame) moving object of the car coming towards you.

What's the answer?

Well probably not a lot without a camera redesign and even then there are limits on what can be achieved in a dashcam at reasonable price. However, the cheap answer that would help, would probably be a higher data rate. More expensive answers would be this plus a higher quality more consistent lens, a faster shutter speed = on a fixed shutter speed camera usually translates to a higher frame rate - the processor often becomes the limit here - how many 120fps dashcams do you know of? and even then if you record a higher frame rate, you need to ensure frames are discarded not blended back to 30fps to retain sharpness (that then can in turn result in jerky "jumpy" video as the car will have changed position noticeably between frames!) - you want blending for smooth video but discarding for sharp stills (so ideally the camera to output eg 120fps to the SD card and for you to choose between blend or discard in post production, not have any frame reduction happen in camera), a smaller aperture (your enemy at night on a fixed aperture camera as a smaller aperture = greater depth of field but less light entering the camera) etc (hence the advantage of an adjustable aperture (I know of no dashcam with one)).

So no easy answer. There are more expensive cameras that help with some of the above in some areas, eg different lens, more resolution, higher frame rate and / or lower compression, but there is no holy grail of dashcams atm that I've personally seen that produces the perfect picture.
 
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