Blackmagic Forum

Hi there

See attached. When I key a white dress in front of a white background, I get this blue shade on the shoulders. The light is pretty much the same all over, but when i move the dummy from left to right the shade shift place.
I can remove some of it with the blue density key, but what is the proper way to get rid of it?
Is it all lightning or color?

Thomas

Hi Thomas,
This could be a lens issue, called a chromatic aberration and some of the newer B4 eng lenses have a solution to this issue called CAC (Chromatic Aberration Correction).
There is a simple test to see if this is the issue. Place the dummy composited against the white in the center of the image, if both sides of the dummy are clean (no blue edge) then it's the lens, try using the CAC in the camera to fix the edges.

If your camera or lens lacks the CAC feature, you can use the U/V FG Input position in the Configure menu on the SR 4to reduce or remove the edges.
Select the Configure Menu>Inputs> On the right side you should see three knobs called FG INPUT U POSITION, FG INPUT V POSITION and FG INPUT UV POSITION> adjust the U POSITION or the V POSITION to remove the blue edge.

Thank you for a quick reply

Indeed the shades disappear in the middel of the shot.
I will try and see if I can remove it one or the other way.

This I would never have thought of.

Thanks

Thomas