3D Artist

KeyShot & Photoshop Tutorial: Render Passes For Texturing and Compositing

Tips & Tutorials
Carrie Mok

Learn how to render out passes and composite them

KeyShot & Photoshop Tutorial: Render Passes For Texturing and Compositing

This tutorial was written by the amazing David Schultz and appeared in issue 106 of 3D Artist. Subscribe today and never miss an issue!

After seeing the rise of the modelling/sculpting concept artist over the last few years, I’ve been trying to figure out some ways I could play around in this space. A lot of what I have done in the past has been more technical and, frankly, slower than where I needed to be to accomplish this, since speed is obviously an important part of creating a concept. So, I needed to figure out ways to get around having to make production-ready meshes and textures (which is very time consuming), and still try to create something that hopefully maintains a higher quality level as a still image. On the sculpting/modelling side, I’ve been using ZBrush and Fusion 360, and discovered some ways to make more concept-level quality meshes in less time, but I still wasn’t happy with what I was doing on the materials and texturing side of things. Last summer, I saw a video of Peter Konig doing some compositing/concepting work at ZBrush Summit, and he showed how he rendered out different materials applied to a model and composited the passes in Photoshop. This may seem obvious to some, but for me it was a revelation. I didn’t need to worry about breaking my mesh up into enough parts for assigning different materials before I rendered out my final image, or setting up complex materials with scratches and dirt that take forever to render.

I could render out passes of different materials and masks from KeyShot, which would enable me to paint in different looks and textures in Photoshop more quickly. In this tutorial, I will go over the way I set up a few materials and masks, and how I use Photoshop to blend everything together.

Step 01 – Render out base materials

KeyShot & Photoshop Tutorial: Render Passes For Texturing and Compositing

Initially, I set up base materials in KeyShot as I am working to help me get an idea of how things will look in the end. The materials in this scene are all standard materials that ship with KeyShot. I rendered them as an EXR with an alpha. If you are familiar with shooting photography in RAW this is the same thing. It just gives you more flexibility in terms of how much it can be modified in Photoshop.

Step 02 – Convert EXR to 16 bit

KeyShot & Photoshop Tutorial: Render Passes For Texturing and Compositing

When you open the EXR in Photoshop, you can reduce the bit depth under Image>Mode to 16 bit. This will bring up an HDR Toning menu. For this image, I just used Exposure/Gamma under the Method dropdown, which gives me the equivalent of what I rendered out in KeyShot. I’ve used the Local Adaptation method on several pieces, and tweaked all of those values to get a better- looking base than what I had straight out of KeyShot.


Step 03 – Define a stress/wear material

KeyShot & Photoshop Tutorial: Render Passes For Texturing and Compositing

I wanted to treat this base armour as if it was a sort of coating over a metal. I know that a lot of armour would actually be made of carbon fibre and other synthetics, but I liked the way it looked having the metal coming through on the edges. To get this edge wear effect, I linked my materials together in KeyShot and dragged Steel Rougher onto my mesh. I rendered out a pass of this. Since this is a reflective material with a higher roughness, it’s going to take longer to render. You don’t have to let the render completely resolve, since we are just going to be using it in really small areas and mostly at lower opacity, and I didn’t mind having some noise in the render.

Step 04 – Create an Occlusion Dirt material

KeyShot & Photoshop Tutorial: Render Passes For Texturing and Compositing

Next, I rendered out an Occlusion Dirt pass. I made a simple material that I saved out to my Miscellaneous folder in KeyShot. The key is to change the occlusion to be Inside. This changes the occlusion to expand further out from the edges instead of remaining in the cavities. You can play with the Radius and Falloff to get the desired look. I decided to blend this with a Fractal Noise, using a Color Composite set to Burn. You can play with the Scale, Levels and Falloff in the Noise node to get the right dirt effect. I wanted it to be a little bit more micro and softer. This just gives the Occlusion Dirt a little extra ‘dirt’ feel.

Step 05 – Stress/wear through masks

KeyShot & Photoshop Tutorial: Render Passes For Texturing and Compositing

In Photoshop, I put a black mask on the render and then used Select by Color Range on the AO dirt and curvature combined with hand painting in the areas I wanted to reveal in the mask. I had three separate layers using this Steel Rougher render. For the first, I used a larger scuffing/discolouration pass on the armour plating, so it’s at a lower opacity of 46%. The second layer I used for some medium wear/distressing, and I used a brush with a larger, rougher alpha. The third layer I used in select areas to act as more distinct edge wear. I don’t do this too much to avoid making it look too over the top.

Step 06 – Get darker grunge

KeyShot & Photoshop Tutorial: Render Passes For Texturing and Compositing

I used the Occlusion Dirt pass and selected areas with Select by Color Range again. It’s probably better to increase the value range and select something that will give you more dirt information to work with, since you will be working subtractively and painting out areas of the mask. I then created two layers with brownish Color Fills (I use fills because I like to be able to easily go back and change out the colours of the whole layer later). I then used that selection and filled it with white in the mask on the Fill Layer. After that, I manually painted away parts of that mask using a brush with a sort of speckled dirt pattern with black and grey values. If you don’t already have custom brushes, go look for some good brushes with dirt patterns. It will make your life so much easier. I use brushes I got a while back from Daarken and then more recently from Maciej Kuciara. They can both be found on Gumroad.

Step 07 – Add in carbon fibre

KeyShot & Photoshop Tutorial: Render Passes For Texturing and Compositing

I rendered out a carbon fibre material pass to use in a few places where I wanted to change the way the materials looked. This can be done at the rendering stage, but I didn’t make this decision until later. I used the Clown pass to start my masking process, and then I had to manually paint, select and fill to refine those masks. I set this layer to Soft Light. Then, under Layer Properties, if you hold Alt and drag the gradient slider called This Layer, you can do a soft clipping of the blacks or whites of your current layer, which enables you to keep the highlights or shadows from the layers below it.

Step 08 – Use Lens Blur and Lens Correction

KeyShot & Photoshop Tutorial: Render Passes For Texturing and Compositing

To finish up, I took all of these layers and created a Smart Object. This enabled me to add filters to all of the layers at once in a mostly non-destructive manner. I used Lens Correction to add in some slight chromatic aberration. Play with the Fix Fringe settings and see what gives you a feel that you like. I think it makes it feel more cinematic. I also used the Depth Mask with the Lens Blur filter to add in depth of field. To do this, put your Depth Mask at the top of the layer stack. Temporarily make it visible. Duplicate it in the Channels and name it Depth. Duplicate your Smart Object, rasterise it and then select your Depth Channel in the Depth Map Source. You don’t want to go too heavy-handed here. I just wanted to blur out the back hoses and the edges of the right arm, to give it a little more depth.


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