What the fill bucket does and why it sometimes fails

The fill bucket in Ibis Paint X is the tool that floods a closed area with solid color in one tap. It sounds straightforward, but it often fills more than you intended, or refuses to fill at all, because the tool is sensitive to how your lines connect. A gap you cannot see on screen — even a pixel-wide break in your outline — tells the fill bucket the area is not closed, so it leaks color across your whole canvas. Understanding why this happens is the first step to controlling it.

The fill bucket has settings that change how strict it is about what counts as "closed." These settings live in the tool options panel, and adjusting them is usually faster than redrawing your lines. The most useful controls are threshold, which decides how similar colors need to be before the bucket stops, and gap close, which lets the tool bridge small breaks in your outline automatically.

Key Takeaways

  • The fill bucket leaks because of tiny gaps in your outline that you cannot see — increase the gap close setting to let the tool bridge them automatically.
  • Threshold controls how picky the bucket is about color similarity; lower numbers fill only exact matches, higher numbers fill similar shades too.
  • Turning on antialiasing detection prevents the bucket from stopping at the fuzzy edges where lines meet the canvas background.
  • Creating a separate layer for outlines and keeping your line weight consistent makes the bucket more predictable across your whole drawing.

Adjusting gap close to bridge small breaks

The gap close setting tells the fill bucket to treat small breaks in your outline as if they were closed. Open the tool options panel — it appears as a horizontal bar below your canvas, or you can tap the wrench icon if it is hidden. Look for the gap close slider, which usually shows a number between 0 and 10 pixels.

Start by setting gap close to 3 or 4 pixels. Tap the area you want to fill. If the bucket still leaks, increase it to 6 or 8 pixels. Higher numbers make the tool more forgiving but also more likely to fill areas you did not intend, so test as you go. If you are working with very fine line art, keep it low; if your lines are thick or sketchy, a higher number prevents constant frustration.

Gap close works best when your outline is a single consistent color. If you have black lines over a white background, the bucket can see the outline clearly. If your lines are the same color as the area you want to fill, the bucket cannot tell where the boundary is, and gap close cannot help.

Lowering threshold to prevent color bleeding

The threshold setting controls how similar a color has to be to the color you tap before the bucket stops spreading. A low threshold (0 to 10) means the bucket fills only pixels that match almost exactly. A high threshold (50 to 100) means the bucket fills a wide range of similar colors, which can cause it to bleed into areas you wanted to keep separate.

If your fill is leaking into shaded areas or antialiased edges, lower the threshold to 5 or 10. If the bucket refuses to fill an area because the color is slightly uneven, raise it to 20 or 30. The right number depends on your image: a flat-color illustration needs a lower threshold than a sketch with soft shading.

Test your threshold by tapping in the middle of the area you want to fill, not on the edge. Edges often have slightly different colors due to antialiasing, and tapping there can confuse the bucket about where to stop.

Turning on antialiasing detection

When you draw a line on screen, the software blurs the edges slightly to make them look smooth instead of jagged. This blur is called antialiasing, and it creates a thin band of semi-transparent pixels around your line. The fill bucket sometimes stops at this band instead of filling right up to your outline.

In the tool options, look for a toggle labeled "Antialiasing" or "Detect Antialiasing." Turn it on. This tells the bucket to ignore the fuzzy edge and treat your line as a solid boundary. If you drew your outlines with antialiasing on (which is the default), this setting usually solves the problem of the bucket stopping short of your lines.

If you drew your outlines with antialiasing turned off — which is rare but possible if you changed the brush settings — leave this toggle off. Turning it on when your lines have no antialiasing can cause the bucket to fill too aggressively.

Using a separate outline layer

One of the most reliable ways to make the fill bucket predictable is to draw your outlines on a separate layer from your fill. Create a new layer, set it above your fill layer, and draw all your lines there. Then create another layer below for your colors.

This separation means your outlines are always a consistent color and thickness, and they sit on top of everything else. The bucket can see them clearly and will not confuse them with the colors you are filling. It also lets you adjust your outlines without affecting your colors, or change colors without redrawing lines.

To set this up: tap the layers panel (usually on the right side of the screen), tap the plus icon to add a new layer, and drag it above your current layer. Draw your outlines there. Create another new layer below for fill colors. Now when you use the fill bucket on the fill layer, it will see the outlines on the layer above and respect them as boundaries.

Keeping line weight consistent

A line that varies in thickness — thick in some places, thin in others — creates inconsistent gaps. Where the line is thin, the bucket may leak through. Where it is thick, the bucket may not reach all the way to the edge. Consistent line weight makes the bucket behave predictably.

Use a brush with a fixed size rather than one that changes thickness based on pressure. In the brush settings, look for "Stabilization" or "Smoothing" and set it to a medium value (around 5 to 8). This makes your lines smoother and more even. If you are using a pressure-sensitive stylus, reduce the pressure sensitivity so thickness changes are less extreme.

If you already have uneven lines, you can redraw them with a consistent brush, or use the stroke stabilization feature to smooth them after the fact. Both approaches take time, but they make the fill bucket much more reliable for the rest of your work.

Frequently Asked Questions

Why does the fill bucket leak across my whole canvas?

Your outline has a gap somewhere, even if you cannot see it. Increase the gap close setting to 5 or 6 pixels first. If it still leaks, zoom in and look for breaks in your lines, especially where curves meet or where you lifted your stylus. Redraw those sections, or use a separate outline layer so the bucket can see your lines more clearly.

The bucket fills the right area but stops short of my lines

Turn on antialiasing detection in the tool options. If that does not work, your threshold may be too low — raise it to 15 or 20. You can also try tapping closer to the center of the area instead of near the edge.

How do I fill an area that has gradients or shading?

Raise the threshold to 30 or higher so the bucket accepts the range of colors in the shaded area. Start by tapping in the darkest or lightest part of the area, not the middle, because the bucket spreads outward from where you tap. If it still bleeds into other areas, lower the threshold and redraw your outline more carefully.

Can I undo a fill if it goes wrong?

Yes — tap the undo button (the curved arrow) or press Ctrl+Z on keyboard, or Command+Z on Mac. Undo works even if you have made other changes since the fill, so do not worry about experimenting with different threshold and gap close settings.

Does the fill bucket work differently on different layer types?

Yes. On a raster layer, the bucket fills pixels. On a vector layer, it fills shapes. For most drawing, raster layers are simpler — the bucket behaves the way this article describes. If you are working on a vector layer and the bucket is not responding as expected, try switching to a raster layer instead.