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I am trying to create an effect where water is frozen in time, resembling the splash of water created by stepping in low water.

My issue is in compositing the borders of my water splash into the water covering the floor.

I've tried multiple shading settings and searched for countless tutorials, looking for one that basically lets me keep all the highlights of the lights bouncing in the splash effect but basically makes it so that its the only thing shown in the layer or a way to softly blend the edges into the water, as in mask feathering.

Further than this I would like to create an invisible layer below the foot that reflects only the particles of the water splash and not the environment map.

I'm not sure whether my solutions would be the right way to accomplish the effect and I'd appreciate whatever solution you might have. (I'm at a semi-beginner level and would appreciate descriptive answers if possible)

Thank you in advance!

-Chris

Image is of the foot and splash effect I'm trying to composite, the edges near the sole being my main issue compositing into the puddle beneath it

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You're not going to find a "tutorial" for this.

You are up for a very challenging task. You need to account for a lot of things, like transparency, refraction, diffraction reflection, caustics in the water, plus the reflections and shadows on the shiny floor and the shoes.

Reflections and transparency have to come from somewhere ,so you will have to put elements to be reflected and shown trough the water.

The most accurate way to deal with this would be to recreate a lot of the scene in blender to make the interaction more convincing.

Try to recreate the material for the floor as close as you can to be able to capture the reflection of the water on the ground and the reflection of the water drops. You will need also a copy of the floor to composite the shadows as a shadow catcher.

To have the transparency of the drops correctly show the background use the image in a plane that is invisible to the camera, but visible to the transparent and glossy elements of the drops.

In reality each drop of water would reflect the entire environment, the window behind, and whatever is behind the camera...

The biggest challenge is that the water on the floor should reflect the shoe as well, but from a perspective that does not exist on the original image, so most likely you need to make the shoe as as 3D element, again invisible to the camera, but visible to the glossy rays. But the water should also be reflected on the floor and at the same time the water should be transparent to show the floor, but there should be some disturbance in the surface of the water caused by the shoe.

You are in for a lot of hours of entertainment while you try things, make masks, play with different rays and multiple layers.

Some info can be found in this post:

How to get reflections from 3D to show up on real images

And then there are many more layers to this onion.

Matching the values for the light values for the scene, getting the correct perspective, etc etc,

Realistic rendering of mesh together with image?

The bottom line is this: compositing is an art, careful studying of how how light and surfaces work in the real world, and attention to small details, and ingenuity to fake things are needed to pull this one off.

Best of luck, and it would be wonderful if you could write a detailed post when you finish: the missing tutorial!

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    $\begingroup$ Could project the image onto the floor. However, replicate the light of the shot is most likely the hardest part if no hdr (captured on set) is available. $\endgroup$
    – brockmann
    Jul 8 '20 at 17:34

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