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Overview

The Fill tool (also called Paint Bucket) floods connected regions with color. It’s perfect for quickly coloring enclosed areas, filling selections, and applying patterns.
Keyboard Shortcut: Press G to select the Fill tool

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Basic Usage

1

Select the Fill Tool

Press G or click the paint bucket icon in the toolbar
2

Set Tolerance

Adjust tolerance in the context bar (0-255)
  • Low: Fill only exact matching colors
  • High: Fill broader color ranges
3

Click to Fill

  • Left-click: Fill with foreground color
  • Right-click: Fill with background color

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Fill Modes

Default mode: Fills connected pixels only
  • Stops at color boundaries
  • Only fills contiguous region
  • Best for: Enclosed shapes
“Connected” means pixels that touch horizontally or vertically, not diagonally.
Toggle between modes in the context bar.

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Tolerance Settings

Tolerance controls how similar colors must be to get filled:
Exact match only
Only fills pixels that are exactly the same color as the clicked pixel
  • Most precise
  • No color variation
  • Use for: Clean artwork with distinct colors
Low tolerance - Similar colors
Fills pixels with very similar colors
  • Small color variation
  • Good for: Anti-aliased edges, slight gradients
Medium tolerance - Related colors
Fills pixels with moderately similar colors
  • Broader color range
  • Good for: Shaded areas, textured regions
High tolerance - Wide range
Fills pixels with widely varying colors
  • Very broad color range
  • Good for: Major color changes, rough selections

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Color Mode Differences

Tolerance works differently depending on color mode:
  • RGB Mode: Compares red, green, blue values
  • Indexed Mode: Compares palette index numbers
  • Grayscale Mode: Compares brightness values

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Fill Options

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Fill in Selection Only

When a selection is active:
1

Create Selection

Use any selection tool to select an area
2

Use Fill Tool

Fill tool will only affect pixels within the selection
3

Respect Boundaries

Fill still respects color boundaries within the selection
This is useful for constraining fills to specific regions without affecting the rest of your artwork.

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Fill Entire Selection

To fill an entire selection regardless of color: Edit → Fill or Ctrl+Shift+F
  • Ignores color boundaries
  • Fills complete selection
  • Faster than paint bucket for solid fills

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Fill Patterns

Fill with patterns instead of solid colors:
1

Enable Pattern Fill

Click the pattern icon in the context bar
2

Select Pattern

Choose from:
  • Built-in patterns
  • Custom brush patterns
  • Imported images
3

Configure Pattern

  • Set pattern scale
  • Choose tile mode
  • Adjust alignment
4

Fill

Click to fill with the pattern
Make your own fill patterns:
  1. Create a small sprite with your pattern design
  2. Select the pattern area
  3. Edit → New Brush
  4. Save to brush collection
  5. Select as fill pattern
For seamless tiling patterns, use View → Tiled Mode while designing to preview how edges connect.

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Advanced Techniques

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Anti-Aliased Fills

Fill anti-aliased artwork without gaps:
1

Increase Tolerance

Set tolerance to 10-30 for anti-aliased edges
2

Use Pixel Connectivity

Ensure continuous mode is selected
3

Fill

Click in the center of the area
Gap Detection: If your artwork has gaps in outlines:
  • Fill may leak into adjacent areas
  • Close gaps before filling
  • Or use lower tolerance
  • Consider filling on a separate layer for safety

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Color Replacement

Replace all instances of a color:
1

Switch to Global Mode

Enable global fill mode in context bar
2

Set Tolerance

  • 0 for exact color match
  • Higher for color ranges
3

Click to Replace

All matching pixels in the layer are replaced
Alternatively, use Edit → Replace Color for more control, including selection of multiple source colors and preview before applying.

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Gradient Fills

For gradient fills, use the dedicated Gradient tool instead:

Gradient Tool

Create smooth color transitions and gradient fills

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Technical Implementation

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Fill Algorithm

Aseprite uses a flood fill algorithm: 
// From: source/src/app/tools/tool_box.h:85
namespace WellKnownPointShapes {
  extern const char* FloodFill;
}

// Fill implementation uses:
// - Queue-based flood fill
// - Tolerance comparison for each pixel
// - Respects selection boundaries
// - Honors layer transparency

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Point Shape: Flood Fill

The Fill tool uses the FloodFill point shape:
  1. Click point becomes seed pixel
  2. Algorithm checks each adjacent pixel
  3. If pixel color is within tolerance: add to fill region
  4. Repeat for all connected pixels
  5. Fill all pixels in region simultaneously
Large fills may take time:
  • Complex shapes: More pixels to check
  • High tolerance: More pixels match
  • Transparent pixels: Additional checks
  • Anti-aliased edges: More comparisons
For very large areas, consider filling selections instead.

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Workflow Examples

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Coloring Line Art

1

Prepare Line Art

Ensure outlines are continuous (no gaps)
2

Lock Line Layer

Lock your line art layer to prevent accidental changes
3

Create Color Layer

Add a new layer below line art for colors
4

Fill Regions

Use Fill tool to color each enclosed region
5

Adjust Colors

Use Lock Alpha ink mode to adjust colors without changing boundaries

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Working with Tilemaps

Fill tool works differently in Tilemap mode:
When working with tilemaps:
  • Fill replaces entire tiles
  • Tolerance compares tile indices
  • Creates/modifies tiles in tileset
  • Respects manual vs automatic mode
In Manual tilemap mode, filling modifies the tileset. In Automatic mode, new tiles are created as needed.

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Ink Modes with Fill

Fill tool respects ink modes:
Ink ModeFill Behavior
SimpleSolid fill at full opacity
Alpha CompositingBlends with existing pixels
CopyReplaces pixels completely
Lock AlphaOnly fills visible pixels, preserves transparency
Change ink mode in the toolbar ink selector.

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Common Issues

Problem: Fill spreads beyond intended areaSolutions:
  • Close gaps in outlines
  • Reduce tolerance
  • Fill on separate layer for safety
  • Use selection to constrain fill
Problem: Some pixels remain unfilledSolutions:
  • Increase tolerance slightly
  • Check for color variations in area
  • Use Edit → Fill to fill entire selection
  • Verify layer is not locked
Problem: Fill takes a long timeSolutions:
  • Reduce canvas size for complex fills
  • Lower tolerance if possible
  • Fill selections instead of large open areas
  • Use Edit → Fill for simple selection fills

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Keyboard Shortcuts

Quick Reference
G           - Select Fill tool
Alt+Click   - Sample color (eyedropper)
Shift+G     - Switch to Gradient tool
Ctrl+Shift+F - Fill selection (Edit → Fill)

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Related Topics

Tool Overview

Gradient

Selection

Color Modes

Layers