How the Grow Command Works in Photoshop

The Grow command in Adobe Photoshop expands an active selection by searching for and including adjacent pixels that fall within a specified color range. Unlike global selection tools, it exclusively targets touching pixels that match the colors of the current selection, making it an efficient tool for isolating contiguous subjects with varied textures or slight color gradations. This guide explains the underlying mechanics of the Grow command, the settings that govern it, and how it differs from related selection tools.

The Core Mechanism of the Grow Command

When you execute the Grow command, Photoshop evaluates the pixels immediately bordering your active selection. The software analyzes the color values of these boundary pixels and compares them to the colors contained within your existing selection. If an adjacent pixel's color values fall within a predefined range of variation, it is absorbed into the selection.

This process evaluates only contiguous pixels. If a pixel matches the target color profile perfectly but is separated from the selection by even a single pixel of an unaccepted color, the Grow command will not select it.

The Role of the Magic Wand Tolerance Setting

The sensitivity of the Grow command is directly controlled by the Tolerance value of the Magic Wand tool, even if the original selection was made using a different tool, such as the Marquee or Lasso.

  • Low Tolerance (e.g., 5–15): Photoshop will only add adjacent pixels that are nearly identical in color and tone to the currently selected pixels.
  • Medium Tolerance (default 32): The command includes adjacent pixels within 32 tonal steps lighter or darker than the pixels in the selection.
  • High Tolerance (e.g., 60–100+): The selection boundary expands aggressively, incorporating adjacent pixels with broader shifts in hue, saturation, and brightness.

To alter how far and aggressively the Grow command expands, you must select the Magic Wand tool from the toolbar and change the Tolerance number in the Options bar before running the command.

How to Apply the Grow Command

  1. Make an initial selection using any selection tool (e.g., Magic Wand, Quick Selection, or Lasso).
  2. If necessary, select the Magic Wand tool and adjust the Tolerance value in the Options bar to control the expansion threshold.
  3. Navigate to the top menu and select Select > Grow.
  4. Repeat the command as needed to step outward across subtle gradients.

Grow vs. Similar: The Contiguity Difference

Understanding the distinction between Photoshop's Grow and Similar commands is essential for precise editing:

  • Grow: Expands strictly to adjacent (contiguous) pixels. It halts wherever it encounters pixels that exceed the tolerance threshold, preserving borders and isolated color fields.
  • Similar: Searches the entire document (non-contiguous) and selects every pixel within the tolerance range, regardless of whether it touches the original selection.

By relying on edge-to-edge pixel adjacency and the Magic Wand's tolerance threshold, the Grow command provides a controlled way to broaden selections without spilling across unwanted boundaries.