Shrink Selection

Feature Shrink Selection
Feature

Shrink Selection

August 16, 2026

✨ A Complete Guide to the Shrink Selection Tool

PhenoCapture’s Shrink Selection tool allows you to seamlessly contract the boundaries of your currently active selection inward. Whether you need to remove a halo of unwanted background pixels around an isolated biological subject or tighten a loose freehand region for maximum precision, this tool handles the boundary calculation instantly.

💡 Key Features

  • Two Shrinking Modes:
    • Quick Default Shrink: Instantly tighten your selection by a standard, preset size with a single click.
    • Custom Pixel Shrink: Need exact control? You can manually specify the contraction size anywhere from 1 to 100 pixels, allowing for perfectly tailored boundary reduction.
  • Smart Shape Handling: The tool intelligently adapts to whatever selection method you are using. It smoothly pulls in the borders of perfect geometric shapes (like Rectangles and Circles) and perfectly traces the complex, irregular contours of freehand polygons or AI-generated masks.
  • Lightning-Fast Processing: Built with a highly optimized internal calculation engine, the tool contracts even the most complex and jagged selection masks instantly, ensuring your workspace remains completely responsive.
  • Safe and Reversible: Directly integrated with PhenoCapture’s undo system. If the contracted boundary is too tight, simply undo the action and try a smaller pixel value!

🛠️ How to Use the Shrink Selection Tool

Step 1: Create Your Initial Selection

Before using this tool, ensure you have an active selection on your image. You can use any tool—such as the Rectangle, Circle, Polygon, or even the AI Auto Subject Selection—to define your starting area.

Step 2: Choose Your Shrink Method

Navigate to your selection menu and choose how you want to tighten the boundary:

  • Click Shrink Selection to quickly pull the boundary inward by the software’s default size.
  • Click Shrink Selection by Pixels… to open a prompt window. Type in your exact desired thickness (between 1 and 100 pixels) and click OK.

Step 3: Apply and Review

The software will instantly calculate the new perimeter and pull your selection mask inward uniformly. If the new boundary isn’t exactly what you need, just use the Undo shortcut and enter a different pixel value!