How to Stop Color Leaks When Flatting
You click inside a shape with the Paint Bucket, and the color floods the whole panel. Or the fill works, but a thin white edge is left along the lines. Both problems have simple causes. Here is why they happen and how to fix them in Photoshop.
Why color leaks through your lines.
A fill tool spreads color until it hits a border. When the border is not there, the color keeps going. There are three usual causes:
- ✓A gap in the line. Even a 1-pixel break lets the color escape into the next area.
- ✓The tool reads the wrong layer. If you fill on an empty flats layer without "All Layers" (Paint Bucket) or "Sample All Layers" (Magic Wand), the tool cannot see your line art, so it fills everything.
- ✓Soft line edges. Anti-aliased lines fade from black to white. The fill stops at the light pixels and leaves a thin white edge, often called a halo.
Fix 1: Close the gaps on a separate layer.
Make a new layer above your line art and name it "gap fix". Zoom in to 200% and draw short strokes with a hard brush, in the line color, wherever two lines should meet but do not.
Keeping these strokes on their own layer means your original line art stays untouched. When the flats are done, you can hide the gap fix layer, or merge it if the new lines look right.
- ✓Use a hard round brush, not a soft one
- ✓Look closely at hair, fingers and folds in clothes, where gaps hide
- ✓Make sure your fill tool can see this layer (see Fix 2)
Fix 2: Use the right tool settings.
Most leaks come from one wrong checkbox. Set the Magic Wand or Paint Bucket like this in the options bar at the top of Photoshop:
- ✓Contiguous: on. Only the connected area you click is filled, not every pixel of the same color.
- ✓Sample All Layers (Magic Wand) or All Layers (Paint Bucket): on. The tool now sees your line art while you fill on the flats layer.
- ✓Anti-alias: off. Flats need hard edges so each area becomes a clean selection later.
- ✓Tolerance: start around 20. Lower it if the fill jumps over thin lines. Raise it if it leaves light pixels along the lines.
If the fill still covers the whole canvas, you are probably on an empty layer with All Layers turned off. Turn it on and try again.
Fix 3: Expand the selection before you fill.
This fixes white edges (halos). Select the area with the Magic Wand, then choose Select → Modify → Expand and expand by 1 or 2 pixels. Now fill on your flats layer, which sits under the line art.
The extra pixels go under the dark line, where nobody can see them. The soft edge of the line now sits on top of solid color instead of white, so the halo is gone.
Fix 4: Find missed spots fast.
Small holes are hard to see on white. Add a layer under your flats and fill it with a loud color, such as bright magenta. Every spot you missed now jumps out. Fill the holes, then hide or delete the magenta layer.
You can also hide the line art for a moment. Areas that merged by mistake are much easier to see when the lines are gone.
Fix 5: Let a tool close the gaps for you.
Closing gaps by hand gets old on a full page. Many flatting tools close small gaps for you:
- ✓Flatte (Photoshop) has a Close gaps setting: off, low, medium or high.
- ✓Clip Studio Paint has a Close gap option on the Fill tool.
- ✓Krita has a Gap close hint on the Colorize Mask.
You can see a leak happen in the Flatte live demo: click Set, click Create flats, then change Close gaps to Off. The ground color leaks into the sky through a small break in the line. Switch it back on and the leak is gone. For a full comparison of tools, read the best flatting tools for comics.
Color leak questions.
We make Photoshop plugins for comic and illustration artists: Flatte for flatting and PixelRec Pro for timelapse recording. We write these guides from our own work in Photoshop.
Close Gaps and Flat
In a Few Clicks.
Flatte closes small gaps for you, turns your line art into clean flat colors, and lets you fix any area without starting over. No generative AI.