Non-photorealistic shading + outline in an illustration aesthetic style

Question

I am working on a project, and I want to replicate the Charles Schulz-esque line style and grain-flavoured airbrush shading. How do I do this in the attached figures in Blender?

Any suggestions would be greatly appreciated.

Answer 1

Textured self shadow

On Eevee, you can achieve that by converting a Diffuse shader into RGB data via the Shader to RGB node, then tweak that a little bit to use is as a mask for two colors/textures:

The Color Ramp changes the limits of the shadow, the Color Burn adds the noise, and then you can use that as a factor for either a mix RGB or a mix Shader.

Flat cast shadow

The edge blurring of shadows is mainly tied to the size parameter of your light objects:

As for its color, it is partially influenced in Eevee by the ambient light or your scene, aka the World Shader color:

You can change it if you want, using a Shader to RGB node:

Lines

There are multiple ways to make lines.

Freestyle

It's a post process render engine that is applied on top of a render made from Eevee or Cycles. Hence, you can't see it from the viewport and have to run a render.
You can enable it in the Properties Editor > Render settings tab > Freestyle panel.

Then most of the settings of how Freestyle behaves is located in the View Layer tab:

Grease Pencil

As explained by @common_goldfish, you can use the lineart system, which under the hood adds an object with a LineArt modifier from the Grease Pencil drawing system. You can add a linerat on a per-object basis, or even on a collection. I.E. you can make a collection Contour with all the object you want to draw a contour line for, and then press ⇧ ShiftA Grease Pencil > Collection Line Art.

This one is visible from the viewport, so it is easier to setup because you can see what it does without having to run a render. But it is drawn from the camera, so turning your viewport around from outside of the render camera will look a bit weird:

Inverted duplicated mesh

The oldest trick when it comes to faking contour in 3D is to make a copy of your mesh, inflate it a bit to the outside, disable the backface rendering and set the diplaced mesh's material to your contour color.

For the duplication and inflation, you can do it manually in edit mode via ⇧ ShiftD then ⎇ AltS. Another simple way to do that in Blender is via the solidify modifier:

This method has the advantage of letting you edit the thickness right from the duplicate mesh itself.

Answer 2

A way to create line art:

Select an object and make your camera view active. You can get the line style by using by shift+a to add a new object, then go to grease pencil choose object line art. This will create a line art modifier, when selected you can adjust line thickness.