Quick process of adapting Megascan Atlas images into volumetric lighting scenes.

If you are like me, and want to use volumetric atmosphere in a scene that incorporates the use of scanned imagery from Megascans (using their 2D scanned imagery known as Atlases) to populate the area, you are out of luck using the standard method of applying the images to planes and use the opacity channel to cut-out the shape. This is because the outline of the plane is still shown in a scene that incorporates volumetric fog/lighting, etc.

To get around this limitation, I have found a moderately quick method to get the look you want with the proper shadows and such. This process involves the use of three software packages. Adobe Photoshop, Adobe Illustrator and Cinema4D and the Megascan Atlas source file(s) from quixel.com.

For this blog, I’m going to talk about incorporating some Seaweed images from Megascans, into my underwater scene. Here is what the scene looks like with the alpha channeled image plane cut-out approach. You’ll notice the planes are easily visible along the bottom of the seabed, even though we ‘cut out’ the shape of the seaweed with the alpha channel/opacity channel of the seaweed.

With the process I’m going to describe below, here is what the scene will now look like:

When writing this blog, I wanted to encompass all levels of experience. So, I apologize in advance if you already know many of these steps. But, hopefully, you’ll still find some useful information in this approach. There are many ways to achieve this look, and so this is just one of many, but it was one I found quick and easy. There are plug-ins that can expedite this process, so feel free to experiment further. I’ve broken the process down to 26 steps. Here they are:

1) Navigate to the megascan library residing on quixel.com to find some seaweed images to use on the seafloor (https://quixel.com/megascans/library?search=seaweed).

2) After selecting the ‘Plant Seaweed’ Atlas that I want to use, I download it to my desktop. You will notice that when you open it up, it contains a variety of files (Albedo, Bump, Specular, Normal, etc.) and that they are in 4K resolution.

Depending on how close you are going to get to the image, you may only need to use a couple of the files. For my purpose, I’m going to use it to populate the seafloor in my scene and don’t anticipate getting very close to it. So, I’ll only use the ‘Albedo’ (for the color) and ‘Opacity’ (for the cutout) images, but feel free to use whichever maps makes the most sense for your project. And I’m also going to reduce the resolution quite a bit since I’m not going to need that much detail and I want to always conserve memory in Octane since I’m running it on either a GTX 1060 or GTX 1070 most of the time.

3) Next, open up all the image files you’ll want to use for your project in Adobe Photoshop (or whichever app you use). In my case, I’ll open the Albedo and Opacity files.

4) Copy and paste each of the image files into layers on the ‘Albedo’ file. You want to have all the channels on one image as layers so that when we crop them, they will all line up perfectly.

5) Once you have that done. Reduce the image to something more appropriate to your needs. In my case, I’m only going to need a resolution of 512×512 pixels. Go under Image>Image Size and select the resolution you want to shrink it to.

6) Then select the ‘Opacity layer’ and select ‘Image>Adjustments>Invert’ to invert the opacity layer to black on white as Adobe Illustrator see’s paths as black on white.

7) It should now look like this:

8) Do a ‘Save As’ of this Photoshop file as a native PSD format file. We are going to create two separate objects from this file. The seaweed on the left and the seaweed on the right. So, use the ‘Crop’ tool to crop the image on the left first. Crop it to as close as you can to the borders of the seaweed image.

9) It should look like this now:

10) Next we will Save out the Opacity and Albedo layers as two separate images. Go to File>Export>Quick Export as PNG and save it as ‘left seaweed opacity’ (or something similar if you aren’t using Adobe Creative Cloud).

11) Next hide the ‘opacity layer’ layer and do another File>Export>Quick Export as PNG and save it as ‘left seaweed albedo’. Since it is the same dimensions as the opacity layer, when we import it into C4D as a texture it will fit perfectly.

12) Now go back several steps to right before we cropped the left seaweed image, so that you will have both images visible again. This time crop the right seaweed and repeat steps 9-11 (naming your files ‘right’ instead of ‘left’ – as I’m sure you already know) 🙂

13) Now we will jump into Adobe Illustrator. Once you have Illustrator open, open up the ‘left seaweed opacity’ file you had saved. Then select the left seaweed image.

14) The open the ‘Image Trace’ window by going to Window>Image Trace, this will pop up the floating ‘Image Trace’ window.

15) In the ‘Image Trace’ window, select the ‘Preset’ drop down menu and choose ‘Silhouettes’ which I found worked well for this image.

16) It’s going to look a little blobby. Don’t worry, we’ll clean it up. Toggle down the ‘Advanced’ arrow to see additional controls. I found that the settings of 180 for the Threshold, 100% for the Paths, 100% for the Corners and 50 px for the Noise created a good clean image. You want to make sure you don’t adjust the Threshold and Noise setting too low or you’ll have free-hanging portions of your image which will import with issues into C4D.

17) Now we want to Save the file out as an Adobe Illustrator format file. File>Save As. Create a folder, or use one you already designated, and name it something logical like ‘left seaweed-opacity.ai’.

18) You will get prompted by a dialog box asking you what version to save it as. You MUST select Illustrator version 8, as C4D only reads that format.

19) Okay, almost there. Now launch Cinema4D and open the ‘left seaweed-opacity.ai’ file. You’ll be prompted by a dialog box asking you what ‘Scale’ you want to bring it in as. I found that for my purposes, a Scale of 0.05 Centimeters and Connect Splines and Group Splines checked, worked well.

20) The imported Illustrator file should look like this in your C4D window. It should come in as a spline object.

21) Next, you’ll want to add an ‘Extrude’ attribute to the imported seaweed.

22) Put the ‘left seaweed-opacity’ spline object under the ‘Extrude’ attribute. Then in the ‘Extrude’ options, select the ‘Object’ tab and make the Z Movement something like .25

23) Now we need to texture it. Create an Octane Diffuse Material and Import the ‘Seaweed Left Albedo’ image we had created earlier and apply it to the Diffuse channel.

24) We need to apply the new material onto the Extruded object. However, change the ‘Projection’ method from ‘UVW Mapping’ to ‘Flat’.

25) Finally, Right-Mouse click the texture icon and select ‘Fit to Object’ and that’s it! Repeat the process for the ‘Right Seaweed’ image and any others that you want to use. You should probably name the file something like ‘Left Seaweed’ so you know what it is as you start importing additional seaweed objects.

26) Now copy and paste this object(s) into your volumetric scene project to replace the decal planes and you have a clean model of the seaweed(s). This process is actually very quick once you understand the process. Hope this helps!

Here is a finished render using the process I outlined in this blog for both the seaweed particulates floating in the water and growing on the seafloor.: