Online Tool Store
· 4 min read
How to Keep an Illustration Set Consistent
Heshan Fernando
Co-founder & COO
The first eight illustrations look like a set. By the twentieth, the line weight has crept up, two new colours have appeared, and the perspective has quietly shifted from flat to slightly isometric.
Nobody made a decision to change anything. Each illustration was made by looking at the previous one, and small drifts compound.
Why sets drift
Consistency by memory works for a handful of images and fails beyond that. The reference is the last thing you made, so each piece inherits the previous one’s small deviations and adds its own.
Over twenty images that produces visible drift, and the drift is invisible one image at a time. It only shows when the set is laid out together — usually on the page it was made for, which is the expensive moment to discover it.
A written specification fixes the reference. Every illustration is made against the same document rather than against the last one, so deviations do not accumulate.
What the specification has to cover
Line weight, in absolute terms and at what canvas size. “2 px at 800 px wide” is a specification; “thin” is not.
Corner treatment — whether line ends are rounded or square, and whether corners are mitred. This is one of the most visible attributes and one of the least often written down.
Palette with limits. Not just the colours but how many may appear in one illustration, and which are for accent rather than fill.
Perspective. Flat, isometric at a stated angle, or a single vanishing point. Mixing these across a set is the most jarring inconsistency.
Shadow and highlight treatment, including whether they exist at all.
Detail level, expressed as what is included rather than a vague adjective — “faces have eyes and mouth, no nose” is usable.
| Attribute | Vague | Usable |
|---|---|---|
| Line weight | “Thin” | 2 px at 800 px wide |
| Palette | “Muted” | Five named hex values |
| Perspective | “Slightly 3D” | Isometric, 30 degrees |
| Detail | “Simple” | Named inclusions and exclusions |
The exclusions matter as much as the rules
A specification listing what to do still leaves enormous scope. The list of what not to do is what closes it.
“No gradients. No drop shadows. No outlines on filled shapes. No more than five colours per illustration. No text inside illustrations.”
Those five lines prevent more drift than any amount of positive description, because they name the things an illustrator would otherwise reasonably add.
They are also what makes a specification usable by someone else. A second illustrator working from a positive description produces something plausible and different; working from a description with exclusions, they produce something that matches.
Include the source files and the tooling
A specification describes the output. Reproducing it needs more.
Source files in an editable format, organised so a second illustrator can open one and see how it was built. A flattened export teaches nothing about construction.
The palette as a swatch file, not just hex values in a document. Hand-entering six colours is where drift begins.
Reusable components — the standard line weights, the corner treatments, any recurring elements — as a library rather than as instructions to recreate them.
Which tool and version, since brush behaviour and default settings differ between applications and even between versions of one.
The specification says what the style is; the source files and swatches are what make matching it practical rather than a test of interpretation.
Common mistakes to avoid
- Using the last illustration as the reference rather than a written specification.
- Describing style in adjectives that two people would interpret differently.
- Omitting the exclusions, which is where most of the constraint lives.
- Specifying at one canvas size and not saying what happens at others.
- Writing the specification after the set is finished, when the drift is already in it.
How to do it with Illustration Style Matcher
The Illustration Style Matcher turns a reference into a written specification.
- Describe or upload the reference whose style should be repeated.
- Set the medium and detail level, which are the attributes people describe most vaguely.
- Use the generated specification as the brief for every subsequent illustration.
- Check the exclusions list carefully — that is the part that keeps a second illustrator on style.
Other design tools are in the tools directory.
Frequently asked questions
Why write a style specification at all?
Because sets drift when each image is made against the previous one. Small deviations compound, and the drift only becomes visible when the whole set is laid out together.
What should the specification cover?
Line weight in absolute terms, corner treatment, palette with a count limit, perspective, shadow handling, detail level, and an explicit list of what to avoid.
Does this generate illustrations?
No. It produces the written specification an illustrator or a generation prompt works from, which is the part that keeps a set consistent regardless of who makes the next image.
Final thought
Write the exclusions. A specification saying what to do leaves room for drift; one saying what not to do is the version a second illustrator can actually match.