vectorcraft/docs/image-trace-adjustments.md

Adjusting an Image Trace

Select a placed raster image, then choose Image Trace or a preset from its arrow in Properties or the Control bar. The original image stays inside the tracing object so that subsequent adjustments always use the original pixels.

To adjust the result, select the tracing object and click Image Trace in Properties or the image icon in the Control bar: the Image Trace panel opens with Advanced expanded. An existing floating or docked panel is activated in its current location. Opening the controls does not add a document undo step.

Control	Range	Effect
Threshold (Black and White)	0–255	Higher values include lighter pixels as black ink.
Paths	0–100%	Higher values fit outlines more closely to the image.
Corners	0–100%	Higher values preserve more sharp turns.
Noise	1–100 px	Suppresses small connected regions; higher values remove more small details.
Method	Abutting / Overlapping	Chooses shared boundaries or stacked overlapping paths.
Create	Fills / Strokes	Creates filled areas, stroked lines, or both.
Ignore Color	Color picker	Leaves out the selected color (white by default).

Sliders apply on release, and their numeric fields can be edited directly. Each committed adjustment re-traces the selected object as one undo step and changes the preset to Custom. While dragging, the preset and Enhanced row stay in place until release so the slider retains its active interaction. Committed settings are synchronized immediately, so Undo also restores the panel values before its next frame. View can show the source image, the result, outlines, or combinations without re-tracing. Use Expand when finished to turn the result into ordinary editable vector objects; after expanding, the tracing settings are no longer available. Release restores the source.

Auto Color (the Automatic palette) counts flat art's colours by area, and also keeps colours too rare for that count when they are distinct and drawn as regions of their own (a stem, a highlight, a white beside a cream), at most six; scattered specks of a colour add none. Adobe does not document how its own palettes are chosen; this is VectorCraft's own method (see image-trace-quality.md).

Keep Colors. "keepColors": ["#rrggbb", …] in the params of imageTrace.make or imageTrace.makeAndExpand traces only the palette colors within about 30 levels of a listed color, the distance Ignore Color matches by, and leaves the other colors out. With Method Abutting, the paths of the kept colors are the same as in a trace of every color. With Method Overlapping, a kept color's paths reach under the kept colors above it in the stack and not under the colors left out, as with Ignore Color. An empty list traces every color, and a value that is not a six-digit hex color is refused. With Ignore Color as well, a kept color that Ignore Color matches is still left out. Flat Logo does not use keepColors: it traces the colors named in logoColors, or the colors it finds. The reply's warnings name each listed color that matches none of the colors the trace found. When nothing is traced because no listed color matches, because Ignore Color leaves out every area of the ones that match, or because the ones that match produce no paths, the first warning says so, and the status bar shows it. In Flat Logo mode the warning says that keepColors is not used.

Abutting and Overlapping. Abutting is the default Method, and the Default, Auto Color, 3 Colors, 6 Colors and 16 Colors presets use it. With Abutting, two neighboring colors share one exact edge. The canvas smooths the edges of each path on its own, so each of the two paths covers only part of the pixels along that edge, and a thin line of the background can show between the colors. Web browsers and PDF viewers usually draw an exported SVG or PDF file the same way and show the same line. Raster exports (PNG, JPEG, TIFF and the other bitmap formats) with None anti-aliasing do not show it at any size. Raster exports with Art Optimized anti-aliasing, the default, do not show it up to 10 million pixels and 16,384 pixels on a side. A raster export shows the line as the canvas does when it uses Type Optimized anti-aliasing, or when it uses Art Optimized and is larger than either limit. Overlapping stacks the colors instead: a lower color continues under the edge of the color above it, and no background shows along that edge.

Large images. An image of more than 1500 pixels on a side is traced as any other, only more slowly, and the trace says so: imageTrace.make returns the note in warnings and the status bar shows it (the results optimization page describes the same warning for images over 1500 px). An image of more than 64 megapixels (up to 192) is traced from a copy scaled down to 64 megapixels, and the trace says that too. Flat Logo traces at most 1024 pixels on a side: a larger decoded raster is averaged down in whole-number blocks first (a 1025-pixel image is traced at 513, and a 16,000 × 12,000 image, decoded at 9,459 × 7,094, is traced at 946 × 710), and the trace names both sizes in warnings. Flat Logo gives that note in place of the slower-trace note for an image over 1500 pixels and in place of the 64-megapixel note. An image at most 1024 pixels on a side is traced at its own size, also when the named logoColors differ slightly from the image's colors. Only an image with more than 150,000 different pixel values that are not exactly one traced color is averaged down further: the factor doubles until at most 150,000 remain or the working copy has at most 16,384 pixels (at most six times). A trace that would make more than 8,000,000 anchor points (2,000,000 on the web) is refused to protect memory, with advice: raise Noise, lower Paths or Colors, or pick a lower-fidelity preset. A trace keeps about 90 bytes an anchor; a 4000 × 3000 photo at High Fidelity Photo makes about 1.9 million. These controls use VectorCraft's existing tracing algorithm. Parameter effects follow its implementation; they do not claim pixel-identical results with another application. The terminology and general control behavior are described in the public Image Trace panel documentation.

Regression coverage: crates/ui-egui/src/panels/image_trace.rs tests opening the panel, a quick trace leaving it as it was, repeated opening, floating ownership, slider commits, visible threshold changes, undo, and the Properties entry point. Tracer tests live in crates/trace/src/tests.rs.