The Fill Bucket tool in Ibis Paint X works best when you adjust three settings: the fill source, the threshold, and the antialiasing option
The Fill Bucket tool (also called the Paint Bucket) floods an area with color, but it often leaves thin white lines around your selection or fills too much of your image. These problems happen because the default settings don't match what you're trying to do. Changing how the tool reads your image, how strictly it matches colors, and how it handles edges will fix most fill problems you run into.
Before you start adjusting, make sure you have the Fill Bucket tool selected. Tap the tool icon that looks like a bucket pouring paint, or press the B key on your keyboard. The tool options panel appears at the bottom of your screen on mobile or in a sidebar on desktop.
Key Takeaways
- The Fill Source setting controls whether the tool looks at your current layer, all layers, or just the selection you made — choosing the right one stops the tool from filling areas you didn't intend.
- The Threshold slider determines how similar a color has to be to the color you click on before the tool stops filling — lowering it prevents overflow into nearby colors.
- Turning off Antialiasing removes the soft, blurry edge that can leave white gaps between your fill and your line art.
- The Expand option grows your fill slightly to cover small gaps that appear after you turn off Antialiasing.
Choosing the right fill source for your layer setup
The Fill Source option tells the tool what part of your image to look at when deciding where to fill. You have three choices: Current Layer, All Layers, and Selection.
Current Layer fills only based on what you see on the layer you're working on right now. Use this when you're filling a layer that has your line art or a solid shape. This is the safest choice because it won't accidentally fill based on colors from layers below.
All Layers makes the tool look at every visible layer at once. This is useful when your line art is on one layer and you want to fill based on those lines, but your fill layer is below it. The tool sees the complete image and fills the enclosed area correctly. However, if you have stray marks on any layer, the tool might stop filling where you don't expect it to.
Selection only fills inside a selection boundary you've already made. This is helpful when you want to restrict the fill to a specific part of your canvas and prevent it from spreading elsewhere.
Lowering the threshold to stop color overflow
The Threshold slider controls how picky the tool is about color matching. At a high threshold (the default is often 32), the tool treats similar colors as the same and fills them all. This causes the bucket to spill into areas you didn't intend, especially in gradients or areas with slight color variation.
Lower the threshold to make the tool more strict. Start by moving the slider down to around 10 to 15 and test it on your image. Click on the area you want to fill and watch what happens. If the fill stops too early and leaves gaps, raise it slightly. If it still overflows into nearby colors, lower it more. The right threshold depends on your image — a drawing with solid, flat colors needs a different setting than one with shading or gradients.
For line art with solid fill areas, a threshold between 5 and 20 usually works well. For images with gradients or soft shading, you may need a threshold between 20 and 40 to fill the entire shaded area without jumping to unrelated colors.
Turning off antialiasing to remove white gaps
Antialiasing is a smoothing effect that softens the edge where the fill meets your line art. It looks good on finished artwork, but it creates a problem during the filling process: the soft edge doesn't match your line art perfectly, leaving thin white or transparent gaps between the fill and the lines.
Turn off the Antialiasing toggle in the tool options. This makes the fill edge sharp and aligned exactly with your line art, so no gaps appear. Your fill will now stop cleanly at the edge of your lines without any blurry transition.
After you turn off Antialiasing, you may notice the fill doesn't quite reach the very edge of your lines in some spots. This is where the Expand option comes in.
Using expand to cover small gaps after antialiasing
The Expand slider grows your fill outward by a small number of pixels. This covers the tiny gaps that sometimes remain after you turn off Antialiasing, especially where lines meet at angles or where your line art is thin.
Start with an Expand value of 1 or 2 pixels. Fill an area and check the result. If small gaps still show, increase it to 3 or 4. If the fill starts to creep over your lines, lower it back down. Most line art looks best with an Expand value between 1 and 3 pixels.
Expand works by pushing the fill boundary outward, so it's most useful on layers where you've already turned off Antialiasing. Using both together — no Antialiasing plus a small Expand value — gives you clean, gap-free fills that respect your line art.
Checking your layer opacity and blend mode
Sometimes the fill looks wrong not because of the bucket settings, but because of how the layer itself is set up. If your fill layer has reduced opacity (anything below 100%), the color will look faded or transparent. Check the opacity slider at the top of the layers panel and make sure it's at 100% unless you intentionally want transparency.
The blend mode of your fill layer can also change how the color appears. If you see unexpected color shifts or the fill doesn't look solid, check that the blend mode is set to Normal. Other blend modes like Multiply or Screen change how the fill color interacts with layers below, which can make the fill look wrong even though the tool worked correctly.
Testing your settings on a practice area first
Before you fill a large area in your actual artwork, test your settings on a small part of the image. This lets you see whether the Threshold, Expand, and Antialiasing settings work for your specific drawing without committing to a fill you might have to undo.
Make a test click in a small enclosed area — maybe a small shape or a corner of your line art. If the fill looks clean and complete, your settings are good. If it leaves gaps or overflows, adjust one setting at a time and test again. Changing multiple settings at once makes it hard to know which one actually fixed the problem.
Keep a note of the settings that work best for your current project. Different images may need different Threshold and Expand values depending on line weight, color complexity, and how clean your line art is.
Frequently Asked Questions
Why does my fill leave white gaps between the color and my lines?
Antialiasing creates a soft edge that doesn't align perfectly with your line art. Turn off the Antialiasing toggle in the tool options, then use the Expand slider set to 1 or 2 pixels to push the fill slightly outward and cover the gaps.
How do I stop the fill bucket from spreading into areas I didn't click on?
Lower the Threshold value in the tool options. Start at 10 and test; if the fill still spreads too far, lower it more. A lower threshold makes the tool pickier about which colors it treats as the same, so it stops at color boundaries more precisely.
Should I use Current Layer or All Layers as my fill source?
Use Current Layer if your line art and fill are on the same layer. Use All Layers if your line art is on a different layer above or below your fill layer, so the tool can see the complete image and fill correctly based on the lines.
What's the difference between Expand and Antialiasing?
Antialiasing softens the edge of the fill for a smooth look but creates gaps. Expand pushes the fill outward by a few pixels to cover those gaps. Use them together: turn Antialiasing off and set Expand to 1–3 pixels for clean fills.
Why does my fill look faded or transparent?
Check the opacity of your fill layer in the layers panel. If it's below 100%, the color will look see-through. Also check the blend mode — if it's set to anything other than Normal, the fill color will interact with layers below and look different than you expect.