Understanding of WDR On / OFF vs EV ( Exposure Value ) Settings

[TeriTerryTarry]

From the Wikipedia article, "In photography, exposure value (EV) is a number that represents a combination of a camera's shutter speed and f-number". Okay, but action cams don't have shutters or adjustable apertures. For the SJCam I guess you could say the aperture is the size of the fixed opening that light passes through. Also from Wikipedia, "the f-number (sometimes called focal ratio, f-ratio, f-stop, or relative aperture) of an optical system is the ratio of the lens's focal length to the diameter of the entrance pupil." The lens on an action cam is fixed so I guess that a fixed aperture and a fixed lens result in a fixed f-number. If that's the case, the only variable left in EV is shutter speed. So on my SJ4000, EV is actually shutter speed, or more accurately the amount of time that the image processor reads the data from the sensor, is that correct?

 

[DT MI]

...So on my SJ4000, EV is actually shutter speed, or more accurately the amount of time that the image processor reads the data from the sensor, is that correct?

I don't have an SJ4000 but in playing with the EV on my SG9665GC that's the impression I get. As I increase EV motion blur becomes more apparent which would be a side effect of an increase in exposure time.

 

[TeriTerryTarry]

I don't have an SJ4000 but in playing with the EV on my SG9665GC that's the impression I get. As I increase EV motion blur becomes more apparent which would be a side effect of an increase in exposure time.

I just did an experiment where I kept all settings constant but varied the EV on my SJ4000 Wi-Fi. I took a series of pictures and sure enough, increasing the EV increased the shutter speed - er, well you know what I mean! That answers that.

Cheers

 

[Nigel]

...So on my SJ4000, EV is actually shutter speed, or more accurately the amount of time that the image processor reads the data from the sensor, is that correct?

The EV adjustment could adjust ISO instead of shutter speed, I don't know if it ever does on your camera but maybe towards the limits of shutter speed it will change ISO in preference. EV+ just means the result will be brighter, the camera can choose to do it in whatever way it likes. "Shutter Speed" should more accurately be exposure time since there is not a physical shutter on an action cam, it is the amount of time that photons are collected for.

 

[TeriTerryTarry]

The EV adjustment could adjust ISO instead of shutter speed, I don't know if it ever does on your camera but maybe towards the limits of shutter speed it will change ISO in preference. EV+ just means the result will be brighter, the camera can choose to do it in whatever way it likes. "Shutter Speed" should more accurately be exposure time since there is not a physical shutter on an action cam, it is the amount of time that photons are collected for.

That was going to be my next question: Since action cams don't have shutters, what does "shutter speed" actually mean? In the experiment I just mentioned the only setting I varied was EV and according to the image properties that is the only property that did in fact vary. The "shutter speed" of the brightest photo was 1/595 sec whereas the darkest photo was 1/9433 sec. Both indicate that the ISO speed remained constant at 100. Is the exposure time the real, actual time that photons are collected or is that some sort of conversion from an equivalent film camera shutter speed?

While we're on the topic, I found this drawing of the "Anatomy of the Active Pixel Sensor Photodiode" from a Florida State University article. I thought it was interesting because it showed that the surface area of a pixel does not consist entirely of the sensor. Other equipment is mounted on it as well.

http://micro.magnet.fsu.edu/primer/digitalimaging/cmosimagesensors.html

 

[kamkar]

The old shutter speed was the time the shutter was open on a camera and exposing the film to light, in modern cameras i think its more fair to call it exposure time.

The time the pixels have to collect light.
Our cameras drop all the way down to 1/30 second in low light, and thats why we see so much motion blur in night footage.
You really want to have a much shorter exposure time when you take pictures or movies of somthing that move 1/250 - 1/500 second at least i would say, but for that you need much more lighe sensetive sensors.

 

[Nigel]

Is the exposure time the real, actual time that photons are collected or is that some sort of conversion from an equivalent film camera shutter speed?

It should be the actual time that photos are collected, and probably is, you can test this by looking at the amount of motion blur, it should decrease as the exposure time gets smaller.

While we're on the topic, I found this drawing of the "Anatomy of the Active Pixel Sensor Photodiode" from a Florida State University article. I thought it was interesting because it showed that the surface area of a pixel does not consist entirely of the sensor. Other equipment is mounted on it as well.

http://micro.magnet.fsu.edu/primer/digitalimaging/cmosimagesensors.html

Our sensors are BSI CMOS sensors - back side illuminated so although there is other equipment mounted on the "front", the light enters from the "back" where there is nothing in the way and the full surface area can be used to collect light.

 

[TeriTerryTarry]

Thanks kamkar1.

Cheers

 

[TeriTerryTarry]

Fascinating stuff Nigel - really very interesting to me.

Thanks again.

 

[kamkar]

I just confirmed the joovuu x camera do not keep on filming at 60 FPS when it get dark, sure the end footage is still 60 FPS but every 2 picture is just a copy of the frames made at 30 FPS.
That way the camera have 2X more time to collect light as opposed to if it was locked in 60 FPS

This is pretty common for all dash and action cameras, sure they might do 60 FPS in daytime, but at night 1/60 second is too little to collect enuff light to make bright footage.
So the camera override 60 FPS menu setting and do 30FPS and then just make a copy of each of the 30 frames to make 60 FPS output footage.

 

[TeriTerryTarry]

I just confirmed the joovuu x camera do not keep on filming at 60 FPS when it get dark, sure the end footage is still 60 FPS but every 2 picture is just a copy of the frames made at 30 FPS.
That way the camera have 2X more time to collect light as opposed to if it was locked in 60 FPS

This is pretty common for all dash and action cameras, sure they might do 60 FPS in daytime, but at night 1/60 second is too little to collect enuff light to make bright footage.

That's interesting kamkar1. Is that referred to as "double frame rate"?

 

[thancam]

WDR is better in static scene. But in action scene, 60 fps or more is better. WDR even become worse in action scene.

 

[quise2024]

Various screenshots from this morning's drive to work

WDR Off EV +2/3

I will be playing with the settings here over the weekend to figure out what i like best. Having a hard time with the openess here and brightness of the sky. I will need to order the CPL as well eventually

 

[Lola]

Very good presentation . I think different cameras evidently effect the quality of the photography in varying degrees.

There is a really good representation of it on this site http://www.techmoan.com/blog/category/car-dvr-dashcams That compares it in his review of the DDPai M3 Plus cam from China also.

I sure wish all cameras came with it.