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View Full Version : Background is affected by Real Camera settings



jdw
03-02-2018, 12:53 PM
I have been doing some composite renders lately (with pre-produced background images) and noticed something odd. When using a "real camera" and setting for a particular camera, the background image is affected by the Lightwave render. I'm not sure if this a bug or by design.

If I'm matching a particular camera, then it should be assumed that whatever characteristics the LW camera / lens imparts on the geometry in the scene (parallax, vignette, brightness, etc) it should leave the background alone -- since it would have already had those artifacts in them when the camera / lens originally captured the image. So, LW "doubles" the effect.

A simple test is to start a new scene. Set the camera type to Real Camera and choose a camera / lens combo (I used Canon SLR / EOS 350D / EF 28mm f2.8). Match the frame size to the image. Set the background / composite to use this image. Now render it.

If you load the original image and the rendered image in Photoshop, you'll see pretty quickly that the rendered image has been changed during the render. In case of the camera I chose, the image is overall darker and has a noticeable vignette.

What you guys think? Should Lightwave leave the background / composite image out of the "Real Camera" process or should it affect it as well? Maybe there is a way to disable "rendering" the background?

I've attached two images -- original NTSC color bars and after being rendered through LW2018 (rendered as described above)
Thanks.

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MonroePoteet
03-03-2018, 04:04 PM
Yes, I see the behavior you mention. It appears that setting the Irradiance Falloff to 0.0 (just below the lens type in the Real Camera settings) eliminates this, and appears to give me my backplate unchanged in the render.

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mTp

jdw
03-03-2018, 04:35 PM
Thanks mTp.

I read the online help section that discusses "Irradiance" and it does manage the vignette effect, but lowering it to 0.0 removes it from the entire scene, not just the background plate. I was hoping there might be a way to convince LW to leave just the background out of the mix, but I'm thinking that it's "all-or-nothing"...

One other thing the "real camera" does is add some lens distortion based on what lens is selected, which would be expected. But LW appears to only distort geometry in the scene, NOT the background. Which causes the original background plate to now be slightly out of alignment with the render. This really messes with things when using a ground plane object with the shadow catcher surface applied to it. Where the edge of the ground plane is visible in a scene, the background will be misaligned.

Setting the same scene to use the Perspective camera will allow the edges of a ground plane object and the background plate to remain perfectly blended with no alignment issues.