Interpolation – Expression in Adobe After Effects: Step-by-Step Guide

Interpolation in Adobe After Effects is the process of calculating in-between frames between two keyframes. When combined with expressions, it becomes a powerful technique to create dynamic animations and control properties smoothly.

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🎯 What is Interpolation?

In simple terms, interpolation is how After Effects fills in the values between two keyframes. There are two types:

• Temporal Interpolation – Changes over time (speed of movement).

• Spatial Interpolation – Changes in space (path of movement).

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🛠️ Why Use Expressions with Interpolation?

Using expressions allows:

• More control over animations.

• Creation of reactive designs.

• Automation of values without keyframes.

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🔧 Expression Syntax for Interpolation

1. linear() Expression

linear(t, tMin, tMax, value1, value2)

➡️ Maps a value t between tMin and tMax linearly to a value between value1 and value2.

Example:

linear(time, 0, 5, 0, 100)

💡 As time goes from 0 to 5 seconds, value changes from 0 to 100.

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2. ease() Expression

ease(t, tMin, tMax, value1, value2)

➡️ Similar to linear(), but with easing in and out.

Example:

ease(time, 0, 3, 0, 360)

💡 Smoothly rotates from 0 to 360 over 3 seconds.

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3. easeIn() and easeOut()

easeIn(time, 0, 2, 0, 100)
easeOut(time, 0, 2, 0, 100)

➡️ Provide acceleration or deceleration only at the start or end.

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4. Interpolation with Slider Control

Link a property to a slider:

1. Add a Slider Control.

2. Use this expression:

linear(effect("Slider Control")("Slider"), 0, 100, 0, 500)

💡 Moves a layer between 0 to 500 based on slider value.

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🔄 Use Case: Move Object Based on Time

x = linear(time, 0, 2, 0, 500);
[value[0] + x, value[1]]

➡️ Moves the layer horizontally by 500 pixels in 2 seconds.

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✅ Tips for Better Control

• Use valueAtTime() to sample values.

• Combine if conditions for reactive animation.

• Use wiggle() with interpolation for randomness.

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🔚 Conclusion

Interpolation expressions help create smooth, flexible animations in After Effects. Whether you’re animating sliders, opacity, or motion, linear(), ease(), and easeIn/out() are your essential tools.