Why is Blender Shadow Catcher not enough?

by Svyatoslav Alexandrov
December 19, 2020

Hey guys! My name is Svyatoslav Alexandrov. In this post, I will show you how to achieve the best shadows on a transparent background in Blender and Adobe Photoshop (or other photo editors). 

Why do we need to get shadows on a transparent background? To compose the initial image with a photo or a solid color background. 

Of course, you can ask me: “What’s your problem, man? Just use Shadow Catcher”. And you’ll be right…and wrong. The Shadow Catcher can’t give us the realistic shadows, but it will be a part of the process.

Please, take look at these renders:

This is a normal Shadow Catcher result. Yes, you can save some time because you render just one image, but you lose the shadow’s quality. It looks like a dirty gray spot because the shadow catcher doesn’t care what background’s color you use. And, of course, you are limited in post-production because the shadow and the object are inseparable.

And here is my method. You render all these layers separately and spend more time, right. But you get the correct color of the shadow. If your background is not just gray, this is really important! And you are free in post-production, you can edit each layer separately because they are independent.

Which way to choose is up to you. If you choose quality, let’s start

Okay. We already created a scene, set up lights and materials, now we need to render our object and shadows separately. What do we need to do?

1. Make sure that your object and background are in different collections
2. The file format is PNG or TIFF
3. The world renders as transparent

Render the object

1. Rename this layer to “Object”
2. Right-click on the “Background” collection – View Layer – Set Holdout or Set Indirect Only. It will remove the background from the camera view
3. You can crop the render region so you don’t render the empty space, it will save some time

Important thing: you should know in advance, what background’s color you will use. It will help you to get correct the color of reflections on the object and shadow on the background. 

Now press F12 and do push-ups or abs. When it’s is finished, save the image, give it the name “Object”.

Render the shadow on the background

1. Create the new view layer, rename it to “Shadow”
2. Right-click on the “Object” collection – View Layer – Set Indirect Only. The object disappeared, but the shadow is still here
3. Crop the render region where the shadow ends

4. Move to the compositing tab and choose in the Render Layers node our “Shadow” view layer

Now render it. Save it as “Shadow”.

Render the same shadow but on a transparent background

We will use this layer as a mask later

1. Choose the background mesh
2. Move to Object Properties – Visibility – Shadow Catcher

Press F12 again and save the render as “Shadow Mask”.

Alright, the work in Blender is done. Now let’s compose all these renders in Adobe Photoshop.

Open all 3 renders in Photoshop, move all images to one file, rename them: “Object”, “Shadow Mask” and “Shadow”. Also, let’s add a background below all layers. Press Shift+F5, select “Color” and take a color sample from our original background. Rename the layer as “Background” and save the file as “Render.psd”.

Now we need to prepare our shadow mask

Let’s create a new layer below the “Shadow Mask” layer, fill it white by pressing Shift+F5 – white, and add the Levels adjustment layer above the “Shadow Mask” layer.
Now adjust it to avoid these dark borders by moving Lights to the left,

and merge all 3 layers, just press ctrl+E (cmd+E if you use Mac).

Hold ctrl (cmd) and click to the layer, press ctrl+C (cmd+C if you use Mac) to copy it,

choose the “Shadow” layer, create a mask,

go to the Channels, turn on this mask and paste the mask by using ctrl+V (cmd+V if you use Mac),

go to Layers and invert the mask.

Deselect the image by ctrl+D or cmd+D. Now you can delete the “Shadow Mask” layer or just hide it if you need it later.

Choose the Multiply blend mode for our shadow. Now you can adjust all layers separately.

I created a YouTube channel where I share my knowledge. The channel is young, it’s really important to get more activity. So please, take a look at my new video, like it and subscribe to my channel.
Thank you for your support, and have a nice day!:)