How to cut out an illustration whose lines are the same colour as the background

Last updated 2026-09-17 · 8 min read

What is the short version?

Keying works by colour, and here the colour is not a distinguishing feature. Set the threshold to clear the background and you lose the shadows in the drawing; set it to keep the drawing and a grey halo stays around it.

1. Tell Vizard Agent the artwork itself contains the background colour.
2. Ask it to select by connection to the frame edge.
3. Ask to see the result on a light checkerboard.

What do you need before you start?

The artwork as delivered and a clear statement of what must survive. Vizard Agent needs to know which dark areas are drawing and which are emptiness, and the only person who can say that with certainty is you.

• The original artwork. Not a re-encode.
• The background colour. Black, white, a flat field.
• What must survive. The darkest strokes, shading, outlines.
• Where it is going. It decides the delivery format.
• Whether it moves. A loop needs the mask to hold.

What do you type into Vizard Agent?

Tell Vizard Agent why a threshold is going to fail. Without that sentence the obvious approach is a colour key, and a colour key happens to be the one method that cannot possibly work on this particular image.

Prompt

Variants worth knowing:

• "A colour key eats them." Explains the constraint.
• "By what touches the edge of the frame." Names the method.
• "On a light checkerboard." Where leftovers actually show.

What does Vizard Agent actually do?

Here is the Vizard Agent sequence on a real illustration that had to be delivered as a transparent overlay. The middle steps carry the whole argument: a threshold is tried, found to be a compromise whichever way it is set, and then replaced with a selection based on connectivity instead.

1. Measures the background to see what separating it would cost.
2. Tries threshold levels that might keep the darkest strokes.
3. Previews the result with the background made transparent.
4. Checks the transparent edge against a light background.
5. Builds a preview on a light checkerboard.
6. Tunes the threshold and finds it still loses detail.
7. Builds the mask from the black region that touches the frame edge.
8. Checks the mask only removes empty field, nothing else.
9. Separates large empty areas from small dark details in the artwork.
10. Rebuilds the mask keeping the details and clearing the field.

Step seven is the method, and it is not a better threshold — it is a different question entirely. Instead of asking which pixels are black, it asks which black pixels are reachable from outside the drawing, and the ones inside a closed outline never are.

Step five is a small discipline with a large payoff. A cutout previewed against the colour you just removed looks perfect by construction; against a light checkerboard, every pixel of leftover background is obvious.

Step nine is where the judgement sits. A large connected field is background; a small isolated patch of the same colour inside the drawing is shading, and the size and position are what tell them apart.

What does the result look like?

An overlay with the drawing intact. The darkest strokes are still there, the outline is not chewed, there is no grey halo, and Vizard Agent shows it to you on a light field rather than on the background it removed.

When does this not work well?

Connectivity fails where the artwork is open. If the drawing has gaps in its outline, the background flows through them and takes the interior with it, and those gaps have to be closed or the region handled separately.

• Open outlines. The fill leaks into the drawing.
• Soft or feathered edges. There is no clean boundary to stop at.
• A background that is not flat. Gradients defeat both methods.
• Photographic subjects. A drawing's hard edges are what make this work.
• Artwork touching the frame edge. It is connected to the outside.

How do you fix a result that came back wrong?

Say whether you have lost artwork or kept background. Those two failures pull in exactly opposite directions, and Vizard Agent treats them as two separate adjustments rather than as one dial to be nudged back and forth between them.

• "The shading has gone." The selection is rebuilt from the edge inward.
• "There is still black around it." The fill is extended or the edge checked.
• "The outline looks chewed." The mask edge is widened back out.
• "It leaked into the middle." An open outline is found and closed.

How does Vizard Agent compare to doing it yourself?

By hand you pull a key, lose the shadows, back the threshold off, get a halo, and settle somewhere in between. The compromise is invisible against the black you removed it from, and obvious the moment somebody puts the overlay on a pale background.

Common questions

Why does a colour key fail here? Because the drawing and the background are the same colour. Vizard Agent selects by position instead.

What is edge-connected selection? A fill inward from the border. It cannot reach anything enclosed by the artwork.

Does this work on white backgrounds too? Yes, and the same trap applies to white highlights inside the drawing.

What if the outline has gaps? The fill leaks. Vizard Agent finds the gap and closes it first.

Why a checkerboard preview? Because leftovers are invisible against the colour you removed.

Can it handle a moving illustration? Yes, though the mask has to hold across frames. Vizard Agent checks it.

Will the edges be hard? As hard as the drawing's own. Vizard Agent does not feather them unless you ask.

What format should I ask for? One that carries an alpha channel. Vizard Agent will tell you which survive.

Can it keep a soft glow around the subject? Say so. Otherwise a glow reads as background and goes.

What about a gradient background? Harder. Vizard Agent will say when neither method separates them.

Does the artwork need to be high resolution? It helps at the edges, but Vizard Agent uses the same method either way.

Can I see the mask itself? Yes. Ask Vizard Agent for the mask, not just the cutout.

What if part of the drawing touches the frame? It is connected to the outside, so tell Vizard Agent to protect that region.

Is this the same as background removal? Same goal, different mechanism — and the mechanism is why it works here.