Automatic Exposure

[NiGMa]

Hi Guys,

I am trying to achieve that video camera look thats been used in alot of the latest games where if you look at the ground the camera adjusts the amount of light it lets in and the image becomes brighter but then if you look up, everything is white for a while until the camera again adjusts and the light let through the virtual iris decreases and the image is clear and not over exposed.

Ok, so what I did is render an animation to a .HDR sequence.
I then loaded that into a LW scene, put it as a background and added the "exposer" image filter on the effects tab. It has a control panel item named Iris Lag, the problem is no matter what I set it to I can get the effect I'm after, it does change somewhat when I change the lag value, but it acts strangely, sometimes like lighting flash changes.



All I'm trying to do is get that nice delay when looking at something bring to looking at something dark. Just like what happens when your outside on a bright day and you walk inside a building.

I tried searching these forums the NT forums and no-body seems to be talking about doing this. Yet I do see it on some renders everynow and then, probably not using LW though.

Anybody know how I can do this? Do any of you guys ever do it?

Thanks =)

heres the vid in XViD = http://www.koscad.com.au/pete/AutoExpose_XViD.avi

[direwolf]

Correct me if i'm wrong, but the delay is not going to smooth the difference in exposure. That would explain the flicker too.

Auto-exposure on camera's use either spot, matrix, etc. to calculate the correct exposure. Full-frame analyzing is most of the times not wanted, since there will always be a small part that is much ligher/darker then the rest of the image. You want these spots to stay that way and just auto-expose the rest of the image. Therefore spot is "better", where the camera uses only a small center circle to analyze.

The solution to your problem is to keyframe the auto-iris-envelope (that the "E" to the right). And turn off the Iris Lag. Keyframe the envelope according to your animation. And then just move your keys futher on the timeline to create a delay.

[direwolf]

I've done some small tests and it works as a charme.

Oke, i realise it's not automatic, but just set a good exposure for outside and find a good exposure for the inside. Then envelop keys from start to end, and where you want the fade.

After that, add Bloom to add some intrest to outblown parts on the inside, whenever you look into a too bright aera.

This way you'll have an easy and quick setup, and get close to your goal.

[NiGMa]

Hey Direwolf, thanks for that, yeah I agree that would work, I thought of doing that but didn't want to because I wanted a totally automatic solution. I don't see why metering the full frame would cause such varying exposures verses spots.

The thing I didn't think of was moving the Envelopes along to get the delay effect! Good thinking, thanks for that!

I will probably go with it, but if anyone else can think of a good way to do this automatically, then lets hear it hey?

[direwolf]

See if i'm right about "Exposure" using a full frame for it's calculation. The guys at the Newtek-forum should know more about this.

About the size of the meteringspot: all digital camera's have it. The cheap models use spot, or small spot only. More expensive types give you the ability to change between modes.

The theory behind this is: the camera will take the average of all pixels and will try to set this as medium exposed. So if you have a very bright or dark spot inside the metering area the camera will takes this into calculation. Therefore it's impossible to shoot directly into the sun, while shooting the sun just outside your metering will not underexpose your photo.

I've added the first link i could find on google about this topic. I've read just the first part, and i think it covers the basics of exposure in photography (and LW-hdr therefore).

http://planetneil.com/tangents/exposure-metering/