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gradual light change needs correction?

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Sarah Lewis
gradual light change needs correction?
on Nov 29, 2010 at 12:50:05 am

Hi
I have a shot that has had an ND filter introduced seconds into shooting so the shot gradually changes from dark to light. It is a documentary and the shot is irreplaceable. Is there a way in FCP post that I can gradually change the light over the period of the shot??
many thanks
Sarah


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Scott Sheriff
Re: gradual light change needs correction?
on Nov 29, 2010 at 1:09:57 am

Keyframe the 3WCC filter.

Scott Sheriff
Director
SST Digital Media
http://www.sstdigitalmedia.com


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Sarah Lewis
Re: gradual light change needs correction?
on Nov 29, 2010 at 1:22:15 am

HI, thanks for you reply - but how do I do this (sorry about the ignorance) Is it with motion control?

Many thanks

Sarah


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Joseph Bradley
Re: gradual light change needs correction?
on Nov 29, 2010 at 1:33:27 am

It's done in FCP. In the Effects window move the 3WCC (three way color correction)filter over the clip. You will probably need to render it out. Then double click the clip and it will open the filter tab in the Viewer window. You can do your keys there.



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Sarah Lewis
Re: gradual light change needs correction?
on Nov 29, 2010 at 2:56:02 am

I understand the keyframe part but how do you change each keyframe to look the same as the final exposure - should I be using 'frame viewer' to compare the end result and the underexposed shots?? When I try and change one keyframe it changes the whole shot for that 10 seconds.
Many thanks for your patience
Sarah


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Michael Gissing
Re: gradual light change needs correction?
on Nov 29, 2010 at 4:12:22 am

You need to keyframe very frame in the 3WayCC until the change stops. Using the scopes, try to match the changes frame by frame of the white level and the gamma. Mostly it will be the whites, but the gamma may make subtle changes as well. Scopes are useful but also trust your eye.


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Scott Sheriff
Re: gradual light change needs correction?
on Nov 29, 2010 at 7:23:39 am

I think I'd start with just 3 Keyframes. One at the last frame before the change, and one at the end of the change, and one in the middle, then see how that works. I would try to match the change with bezier curves (handles), and only ad more KF's as a last resort. If you use to many KF's the change will look 'steppy'.

Scott Sheriff
Director
SST Digital Media
http://www.sstdigitalmedia.com


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Scott Sheriff
Re: gradual light change needs correction?
on Nov 29, 2010 at 8:02:27 am

I'm not sitting in front of the Mac at the moment, but I don't think you can have KF bezier 'handles' on the controls in the 3wcc in FCP.
I should have been more specific when I wrote the above post. You can have bezier curves in Motion, which is where I was thinking I would do this. You can use the Keframe editor to have a nice ramped change in Motion.

Scott Sheriff
Director
SST Digital Media
http://www.sstdigitalmedia.com


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Bill Lee
Re: gradual light change needs correction?
on Nov 30, 2010 at 7:47:07 am

In general, you select the clip you want to correct over time, then select the Color Corrector 3-way from the Effects>Video Filters menu. Once done, press the Enter key to bring that clip and filters into the Viewer. You should now have a Color Corrector 3-way tab in the viewer; click on that tab. Move the playhead in your timeline to the start of your clip; you should see the playhead in the Color Corrector 3-way tab also move to where the clip starts. Press the Ins/Del Keyframe button in this Color Corrector 3-way tab to lock down some initial color correction settings at this stage (don't worry if they are not correct yet). Move the playhead to the last frame of the clip you are correcting; this should also move the playhead in the Color Corrector 3-way tab to the end of your clip. Press the Ins/Del Keyframe button in this Color Corrector 3-way tab to lock down some color correction settings at the end of this clip. Before you add any more keyframes, watch your clip. Note down any sudden changes in lighting, since you will need to keyframe these points. Keyframes will default to linear changes between two keyframes, so if your lighting doesn't change linearly, you will need to change the default curve (i.e. straight line) between two keyframes.

Move the clip playhead to the first keyframe (also the first frame of this clip). Use the Color Corrector 3-way to tweak the color/luminance so it looks right. Move to the last keyframe in the clip and use the graphical interface tab for the Color Corrector 3-way to get this last keyframe right. Use the Match Hue feature to get things almost right very quickly for both of these keyframes. (Use the Help if you don't know how to use this feature.) If you don't have any keyframes except for the beginning and end frame keyframes, then great!, otherwise go to the intermediate keyframes and make their color 'right'. Use the Tools>Frame Viewer to compare two frames to get a closer match.

If your lighting does not change linearly over the clip duration, you may have to tweak how the changes in parameters vary. Click on the Filters tab in the Viewer, then open the Color Corrector 3-way (numerical) filter. You should see a bunch of parameter names, their values, and on the right the keyframes and how these parameters change linearly as graphs. You probably want to get some more space for the parameters which don't change linearly, so move the arrow cursor over the bottom line which separates a parameter graph from the next graph. The cursor should change into a one way resize cursor; click and drag downwards to make the graph big enough to work with. Now move the (arrow) cursor over one of the keyframes for that graph and it will change into a cross-hair cursor. Right-click over it; a pop up menu with Clear and Smooth will appear; select Smooth and you will get an adjustable handle from that keyframe that will let you adjust how the parameter changes near that keyframe. Usually if you do one keyframe, you need to also Smooth at the keyframe at the other end of what was the straight line before. Adjusting individual parameters via the numeric filter tab can be quite time consuming with unexpected results if you change some parameters and not others, so try to get it right with the Visual interface of the Color Corrector 3-way before delving into the numerical parameters.

Bill Lee



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Sarah Lewis
Re: gradual light change needs correction?
on Nov 30, 2010 at 11:14:07 am

Hi bill, thanks so much for that extended description- it is much more what I needed and I really appreciate you taking the time to write it. So I will let you know how I get on. Many thanks, sarah


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