8mm Forum: Chromatic Aberration question...

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Posted by Bryon Fields Harrington Jr. (Member # 3210) on March 21, 2013, 03:57 PM:

I would like to start with my setup at my location to transfer 8mm film. I use the Elmo TRV-8 telecine system that goes out to a ADVC. The ADVC goes into my iMac via Firewire which is then captured by Final Cut Pro.

I was recently transferring some 8mm reels and I noticed some chromatic aberration in a few frames of the footage. I could see that there was purple fringing on some of the highlights of the film that are a little distracting, but hard to notice unless you slow down the footage in Final Cut.

So, is the chromatic aberration a result of the camera from the TRV-8 or is it from the lens that the film was originally shot with?

And if the TRV-8 is the problem is there a way fix the aberration in post? Or could I fix lens that is in the TRV-8?

I have attached a few examples just in case my explanation was not clear.

thank you

all is well

Posted by Douglas Meltzer (Member # 28) on March 21, 2013, 10:52 PM:

Byron,

My first assumption is that this is a result of the lens of the CCD camera on the TRV, however here a few questions to narrow down the problem.

Can you screen the footage on non-telecine projector?

When you look at the footage frame by frame in FCP is the fringing consistent, or does it appear intermittently?

I've seen this before in overexposed parts of the frame but here it appears to be in darker parts as well. It almost looks like light being refracted off the lens coating.

As for color correcting in post, you can use the 3-Way Color Corrector in FCP to remove that part of the spectrum and decrease the saturation, but of course that will affect the rest of the image.
CoreMelt has a set of color correction plug-ins called "Pigment" which includes one for purple fringe reduction. It's part of their Editors Tools package.

Doug

Posted by Bryon Fields Harrington Jr. (Member # 3210) on March 22, 2013, 10:34 AM:

Hey Doug,

Thanks for responding so quickly to my post.

Unfortunately I can't screen the footage with a non-telecine projector because I don't have one at the moment.

As for the fringing, it appears intermittently throughout the footage. And you are right the fringing does appear on the darker areas of the film and the over-exposed areas of the footage.

I will take a look at Coremelt today to fix the problem in post for now. I tried using the 3-way Color Corrector in FCP but it makes the footage look even worse after decreasing the saturation.

Do you have any suggestions about fixing the lens in the TRV?

Thank you

fields

Posted by Douglas Meltzer (Member # 28) on March 22, 2013, 04:10 PM:

Bryon,

Could you use my email link and send me 10 seconds of footage?

I'd like to take a closer look.

Doug

Posted by Bryon Fields Harrington Jr. (Member # 3210) on March 25, 2013, 10:07 AM:

Hey Doug,

I sent you a short clip of the footage this morning. Let me know what you think.

thanks again

fields

Posted by Douglas Meltzer (Member # 28) on March 26, 2013, 11:50 PM:

Fields,

Thanks. I'm on the road this week. I'll check out the clip when I return next week.

Doug

Posted by Douglas Meltzer (Member # 28) on April 04, 2013, 07:55 PM:

Fields,

I stacked the clip in FCP and desaturated the bottom copy. I then tried keying the purple out on the top clip so that the desaturated areas would come through, however the difference was minimal. Sorry, I was hoping that would do the trick.

Doug

Posted by Maurizio Di Cintio (Member # 144) on April 04, 2013, 08:09 PM:

Hi, Doug!
Regardless of the results, your process is terrific!!! What did you use?

Posted by Douglas Meltzer (Member # 28) on April 05, 2013, 02:13 AM:

Maurizio,

I'm guessing you're asking about which filters? I used Chroma Keyer to try to isolate the purple, and Color Corrector to desaturate the bottom clip. This is in FCP 7, by the way.

Fields,

I tried again and had a little more success:

I lost most of the purple in the upper right and left parts of the chair, also in that middle spot, but not all. Expanding the spectrum of the key affected too many of the other colors.

Here are my settings:

Doug

Posted by Bryon Fields Harrington Jr. (Member # 3210) on April 09, 2013, 06:11 PM:

Hey Doug!

your results are great, thank you for getting back to me. I did some research on chromatic aberration and I am still confused why this happens. I am glad that you have found out how to resolve this problem in post, but what actually causes this problem in the first place?

I will use your settings to see if this solves my problem. Thank you again

all is well

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