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How to reduce Chromatic Abberation in Post?

AndreasOberg

AndreasOberg

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Hiya!

Any tips on how to reduce chromatic abberation in post from lenses?

For still photography I have found Lightroom to be stellar in removing chromatic abberation. Often most or all can be removed (but not always). However how do we deal with this for videos?
Does Davinci have a way of doing this?
After Effects?
Redcine?

I have considered rendering out to still images and running a pass in Lightroom, but would really like to avoid that if possible. I'm also not sure if Lightroom will introduce artifacts for moving images since it's not really meant to deal with videos.

Lets just crush those evil purple fringes!
/Andreas
 
I use a secondary color corrector. A lot of times I'll do it right in Premiere just by highlighting the green or purple, expanding out the selection and desaturating it enough to where it's unnoticeable. Those colors are usually vibrant and odd enough that it rarely effects other things in the frame. And if the colors were prevalent in the frame then the CA itself wouldn't jump out so much.
 
Justin McAleece said:
I use a secondary color corrector. A lot of times I'll do it right in Premiere just by highlighting the green or purple, expanding out the selection and desaturating it enough to where it's unnoticeable. Those colors are usually vibrant and odd enough that it rarely effects other things in the frame. And if the colors were prevalent in the frame then the CA itself wouldn't jump out so much.
Click to expand...

chromatic abberation is a prism effect, that means that the picture is skewed / scaled differently along the color spectrum so desaturating it is nor really solving it, it might be less visible but it still brings blur to your image. So better to skew or most normally scale the 3 different channels of colors so that they match up. Most compositing applications can extract an image into r,g and b as BW images those you can line up (normally scaling from center of image is enough) but some lenses also warp the color chanels so then a mesh warper or such is needed to align them. When thats done you composite the three chanels together again and then the problem is solved and even if you turn your picture black and white you will have sharper corners etc from going that route. Best is to do this process and also rectify (defisheye) your footage at the same time so you do not need to resample twice and off course this is all something that benefit to be done in full capture resolution before downsampling as that give the best result possible.

Normally you can use one setup per lens even though it differ a bit with focus and iris etc. But for our lenses I got one setup in flame for each lens that just makes them as mathematically perfect as possible. Even though I personally usually like some lens oddities so a lot of times I run the footage through so it gets "flat and correct" and then do the vfx work and then reverse the setup so it goes back to its original with all the CG in it.
 
Björn Benckert said:
chromatic abberation is a prism effect
Click to expand...

Bjorn is on it. Its not an easy fix. I've done it in the past with stills by doing RGB separations and then distorting (Fisheye or inverse fisheye effects at very low settings) to fix it. This all sounds fun and fine but Resolve isn't really set up to properly do that. The desaturation method works, sort of. I often find that older or cheap lenses most seriously exhibit pink fringing around ultra bright highlights so an HSL key on hot pink can remove the pinpoints of bizarre color - If you talent isn't wearing pink! The proper way to really fix the entire image is with something like Nuke as is mentioned above.
 
Michael

I think in V10 is it almost possible using a mix of the new node sizing and channel mixer node. You can finally separate the three channels in resolve into seperate nodes and work on the independently. And nodes have individual sizing. Now if resolve just had a mesh warper
 
Björn Benckert said:
chromatic abberation is a prism effect, that means that the picture is skewed / scaled differently along the color spectrum so desaturating it is nor really solving it, it might be less visible but it still brings blur to your image. So better to skew or most normally scale the 3 different channels of colors so that they match up. Most compositing applications can extract an image into r,g and b as BW images those you can line up (normally scaling from center of image is enough) but some lenses also warp the color chanels so then a mesh warper or such is needed to align them. When thats done you composite the three chanels together again and then the problem is solved and even if you turn your picture black and white you will have sharper corners etc from going that route. Best is to do this process and also rectify (defisheye) your footage at the same time so you do not need to resample twice and off course this is all something that benefit to be done in full capture resolution before downsampling as that give the best result possible.

Normally you can use one setup per lens even though it differ a bit with focus and iris etc. But for our lenses I got one setup in flame for each lens that just makes them as mathematically perfect as possible. Even though I personally usually like some lens oddities so a lot of times I run the footage through so it gets "flat and correct" and then do the vfx work and then reverse the setup so it goes back to its original with all the CG in it.
Click to expand...

Obviously that is assuming, that someone had a foresight to shoot a sizing chart. Without the sizing chart removing the lens distortion is more difficult, but not impossible. You'd hope that there will be some horizontal and vertical lines in the image. Even assuming, that there is none, PFTrack still does decent job removing lens distortion without the chart, but then you need a decent length video with a lot of spacial information, so PFTrack will do proper camera tracking in order to be able to calculate the lens length used for un-distorting. But if you combine the Mocha Pro lens distortion module, Resolve's color channel alignment and the sizing chart you can get decent results relatively painless.
 
Thanks for the responses guys. Very informative. It does indeed sound quite a bit more complicated than for stills, but still doable.

I will do some tests and see how Lightroom handle Red moving material since it would be reasonable easy to process frames like this and then maybe trying something along what Bjorn suggests.
Cheers!
/Andreas
 
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