Hello! Welcome back to your digital art training.
In the last lesson, we established the fundamental principle of light and shadow: how a light source divides any object into a light side and a shadow side, separated by the terminator. You practiced predicting the basic shape of this shadow based on the light's direction.
Today, we're going to add a layer of sophistication to that model. The "shadow side" isn't just one uniform area of darkness. It's composed of two distinct types of shadows that work together to create the illusion of three-dimensional space. Our learning outcome is to distinguish between form shadow and cast shadow.
Understanding this distinction is a non-negotiable step toward realistic rendering. It’s what makes objects look like they're sitting in an environment, rather than just being flat shapes on a page. This concept will be crucial when we begin rendering the complex forms of the human body, where muscles and limbs cast shadows on each other.
1. The Two Types of Shadow
Let's start with a very direct and clear definition.
Go From Flat to Realistic Shading! Here’s How
The Proko channel offers some of the most concise art education available. This very short clip gets straight to the point in defining our two key terms.
Watch the clip from 02:48 to 03:15. Listen carefully for the definitions of form shadow and cast shadow.
As the video explains:
- Form Shadow: This is the shadow that appears on the object itself. It occurs on the parts of the object's surface that are turned away from the light source. The form shadow begins at the terminator line.
- Cast Shadow: This is the shadow that the object projects onto another surface (like the ground, a wall, or another object). It's created because the object is physically blocking the light from reaching that surface.
Let's look at this visually.
Think of it this way:
- The form shadow reveals the object’s own three-dimensional shape. It describes the curves and planes of the object itself.
- The cast shadow anchors the object in its environment. It reveals the object's position relative to the light source and other surfaces.
2. Characteristics of Form and Cast Shadows
While both are "shadows," they behave differently and have distinct characteristics.
Form Shadow
The form shadow is all about the object's volume. Its edge is the terminator. On a curved object like a sphere, this edge is often soft and gradual because the surface is slowly turning away from the light. On an object with hard edges like a cube, the terminator will be a sharp, geometric edge.
A key part of the form shadow, which we'll explore more in the next lesson, is the core shadow.
Digital Drawing for Beginners: Basics of Digital Shading
This article from artist Monika Zagrobelna provides clear, written definitions for key lighting terms. We'll use it to define the 'core shadow'.
Read the short subsection titled 'Terminator and Core Shadow'. This will formally introduce you to the core shadow, which is the darkest area within the form shadow.
As the text explains, the core shadow is the area on the object just beyond the terminator. It's often the darkest part of the form shadow because it's the area least likely to be illuminated by light bouncing from surrounding surfaces.
Cast Shadow
A cast shadow's shape is a projection. Its shape depends on two things: the silhouette of the object blocking the light, and the shape of the surface it's falling on. If a cast shadow falls across an uneven surface, it will wrap and distort around the contours of that surface.
How do you determine the shape of a cast shadow? It's a matter of geometric projection.
Understanding Light and Shadow | How to Shade Digital Art in Procreate
In this video, artist Alex Huneycutt demonstrates a very systematic way to construct accurate cast shadows, which may appeal to your developer background.
Watch from 03:18 to 04:22. Notice how the artist draws lines from the light source, past the corners of the cube, to find the corresponding points for the shadow on the ground plane. You don't need to master this technique right now, just understand the principle: a cast shadow is a logical projection.
The key takeaway is that a cast shadow isn't random; it follows predictable geometric rules based on the light source and the object's form.
3. Applying the Concepts to Complex Forms
This distinction is not just academic. It's the foundation for shading anything complex, including the human figure. When you draw an arm, it has form shadows that describe the roundness of the biceps and forearm. It also casts a shadow onto the torso.
Let's see this in action.
Understanding Light and Shadow | How to Shade Digital Art in Procreate
Let's return to Alex Huneycutt's video to see how these principles are applied directly to figure drawing.
Watch from 07:32 to 08:45. The artist talks about 'shadow mapping'. This is the process of first identifying all the terminator lines on the figure's forms (the cylinders and boxes of the arms, legs, and torso) and then filling in the resulting shadow shapes. This is a powerful demonstration of identifying and separating form shadows on a complex subject.
This "shadow mapping" approach is a fantastic way to simplify a complex problem. Before you worry about blending or details, you first solve the puzzle of "where are the form shadows?" This directly connects today's lesson to your ultimate goal of drawing the human body.
4. Practice: Isolate and Identify
Now it's your turn to apply these concepts. This exercise is designed to make you consciously separate the two shadow types in your mind and on the canvas.
Estimated Time: 20 minutes
- Setup: In Procreate, create a new canvas. Draw a simple ground plane (a horizontal line).
- Create Objects: On a new layer, draw a sphere floating slightly above the ground plane. To its right, draw a cube resting on the plane.
- Establish Light Source: On a separate layer, draw a small arrow indicating a light source coming from the top left.
- Block in Form Shadows:
- Create a new layer. Name it "Form Shadows".
- Select a medium-gray color.
- For both the sphere and the cube, paint in the areas that are turned away from your top-left light source. The right and bottom faces of the cube will be in shadow, and the lower-right side of the sphere will be in shadow.
- Block in Cast Shadows:
- Create another new layer below your object layers. Name it "Cast Shadows".
- Using the same gray color, think about how the objects would block the light.
- Draw the shadow that the sphere casts onto the ground. It will be an ellipse to the right of the sphere.
- Draw the shadow that the cube casts. It will also be projected to the right.
- Challenge: The sphere is floating. Part of its cast shadow will fall on the ground, and part of it might fall onto the side of the cube. The cube's cast shadow might overlap with the sphere's. Try to visualize and draw this interaction.
The goal is not a perfect rendering, but to use layers to physically and mentally separate the form shadows from the cast shadows.
Conclusion
Great job! You've now dissected the shadow side of an object into its two main components. This is a major step up in your understanding of how light and form interact.
Key Takeaways:
- Form Shadow exists on the surface of an object and describes its volume. It begins at the terminator.
- Cast Shadow is projected by an object onto another surface and describes its position in space.
- The shape of a form shadow follows the object's own contours.
- The shape of a cast shadow is a projection, determined by the object's silhouette and the surface it falls on.
In our next lesson, we will focus on rendering these shadow shapes. We'll learn to use smooth blending to create gradients from light to dark, and we'll officially define all the parts of the light and shadow family: halftones, core shadows, and reflected light. You have now built the solid foundation needed to tackle that next step.