Comping Explosions

Hi Everyone,

I’ve been tasked tasked with comping some distant explosions on a night sky within an Aces project. Easy so far i hear you say. Here’s the catch. I have to do them on day light plates working under a day for night LUT the colourist has supplied me.

For the life of me i cant get this looking anywhere near presentable as the blurs, colours blends look awful under the working lut. This is because i’m trying to push the colours so far its all falling to bits with hard edges and other delightful horrors.

Am i flogging a dead horse or does anyone know a technique to get this done. I feel i want to work ontop of the LUT then invert the result but this isnt happening with the supplied LUT.

Any ideas would be as always most appreciatted.


So youre comping to the day plate then applying the LUT? That would be my way of working as it could be a problem with the LUT pushing things too far.

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Surely you are going to need to grade down the plate in comp to some degree? I just don’t know how you would get the light properly interacting with the surrounding landscape on a day plate. It will just look terrible.

I wonder if you put some kind of colour transform/grade to grade it down, comp your explosion in then invert the colour transform at the end of your comp? I reckon you will still get some funkiness happening on that.

It’s not like you could shoot a real explosion as day for night then be able to grade that and make it look realistic either.

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LUTs are not perfect. They are just giving you an idea of how it might go in the grade.

I can believe how your day for night LUT might be making a royal mess of your explosions.

However any adjustments or grade you apply to make the shot easier to work with will drastically effect how the LUT will work. Potentially breaking the viewing LUT entirely.

You could, for example apply a colour correction yourself. Making the day plate look like night so that you can comp your explosion. You would probably be expected to invert that colour correction so that you return the plate to the colourist. Applying a LUT is not something that is reversible without messing up the original image.

Have a read of this Invert Colour Grade

This might still look terrible under the provided LUT but at least you know that a talented colourist would be able to make it work by applying a similar grade to you. If you make your own CDL you can even provide this with your shot.

However it seems like before you get too far down this road you ask some questions. If you have a VFX supervisor or maybe you can approach the colourist or producer that you are supplying the shot to.

Seems to me that request might be testing the limits of the provided LUT and maybe the workflow can be tweaked on this occasion.

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Thanks everyone. I’ve had a long chat with the colourist this morning and we have decided this just isnt going to work as i didnt think it would.

You guys hace also pretty much confirmed this so thank you.

Our solution is to do the comp on the lutted plate and a soft edge mask on the graded plate and a tweek should do the trick. I am however intrigued and looking foward to read about inverting a colour grade. Many thanks everyone. Really appropriate as always the advice i get.

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yea thats a hard one, this is one of the main issues I have with shotgrade luts personally.

On a previous shoot where they would do day for night we had the same problem, so we ended up doing the day for night in comp with no lut, only taking a dpx of the grade as a ref.

looked much better anyhow