Cinerender Background Image

[adamsb]

Hi All,

When I render using cinerender and include a photo image as my background image, the exposure settings from my "physical camera" cause my background image to be overexposed. I have a physical sky turned on, but "sky visibility" is turned off.

Does anyone know how I can make cinerender not affect the background image?

Thanks!

[adamsb]

Hi again, thought I'd bump this back up. 151 views and no replies. Admins any idea if it's possible to not affect the background image?

[Anonymous]

What default setting did you start with? Show screen shots of your detail settings to get more help and maybe a rendered image?

[Karl Ottenstein]

I just ran a couple of dozen test renders with a background image from the library (sky_trees2_photo.jpg set at 'scale to fill'), and everything behaved as I thought it should. The physical camera works exactly like a real camera for me giving very nice results. If your background image is overexposed, then your scene is not illuminated sufficiently, requiring you to boost the camera's ISO speed, decrease the shutter speed, or open the aperture (lower f value) to expose the scene more.

With proper lighting, the result is very good for scene and background... and adjusting the camera overexposes or underexposes both equally.

Besides your sun time/date of course (assuming you're doing an external render and not looking out windows from inside), you do want to be sure that you have global illumination enabled.

[adamsb]

Karl,

Okay, so the reason my background photo became too dark is because my ISO and other Physical Camera settings are incorrect. Does that mean that the only way to get the background image to look like the original photo is to make the Physical camera settings have no affect? I'm not sure how this camera becomes a useful tool anymore then. Why not turn this physical camera off altogether?

Is it providing a different use that I'm missing?

Thanks so much for your help!

[Karl Ottenstein]

No - the way to get the background to look 'right' is to properly illuminate your scene so that it matches the (implied) illumination of your background image. Then, any camera adjustments affect each about equally.

For example, if you have a normally lit scene, but the image file that you choose for a background is underexposed, you'll wash out your scene if you open the lens enough to properly expose the background image. In your original example, it sounds like your scene was not illuminated enough, and so when you ask the camera for a longer exposure (e.g., lower f-stop and/or slower shutter and/or higher ISO speed) to show your scene properly, it then overexposed your background.

With an HDRI background, I assume this wouldn't be an issue ... since in that case, the HDRI image is illuminating the scene and so they are guaranteed to be in the same lighting realm. I haven't played with HDRI much with CR yet... Eduardo and others can give feedback there.

Comparison info on physical renderer (and physical camera) vs standard render:

http://helpcenter.graphisoft.com/guides/archicad-18-int-reference-guide/user-interface-reference/dia...

What kinds of results do you get with your background image with the standard renderer, with global illumination enabled/etc?

[adamsb]

Thanks Karl, that makes sense. Plenty of help on that link too!

I'll look into my setting to see why I'm off with my lighting levels.

[adamsb]

Karl,

As I think about the process a little more, it seems that it would be nice to still be able to check on a box somewhere that tells cinerender to simply not affect the background image.

This image, which is the existing site without the building almost always, has already been taken using a camera that has applied some level of exposure control to the environment. Why should we have to over-light our model simply to try to affect the background image SO MUCH as to then apply the physical renderer to it to look the way it did when I first took the photo? Just leave the background alone, and I'll affect the model with lighting to match!

Doesn't that make more sense to you too?