A trace does not cut the paper straight away. Its shapes wait on the sheet, above the photo and filled in cyan, until they are flipped, so you can look at them, reshape them, trace again or throw them away first.
What it does
When you press “Trace”, the shapes are clipped to the art board and join the waiting shapes: shapes that exist but have not yet cut anything. Tracing adds nothing to the undo history. The preview goes back to “Photo”, and on a phone the settings sheet closes so that you can see the result.
Each waiting shape is judged, as a drawn shape is, by the paper under it:
- Over front paper, it is a cut. Flipped, it cuts a hole and folds the piece out over an edge.
- Over a hole only, where paper has already gone, it puts paper back.
- Over a real measure of both, more than 5% of each, it becomes a question for you: “Take” or “Put back”.
- Lying mostly off the sheet, over the ground, it is first mirrored onto the sheet, across the edge of the folded piece it covers or else the nearest edge: out there you traced where paper lands. Then it is judged by the paper it lands on, without the “Take” or “Put back” question.
What happens next depends on the flip mode, in the “Flipping” section of the Controls tab (see Flipping):
- “Each shape” (the default): the questions come at once. If any shape needs “Take” or “Put back”, that is asked first, once for all of them; then the direction chooser opens, and one direction flips every waiting shape. After the flip the photo is hidden so that you can see the cuts, and the eye in the Trace panel's heading brings it back. Press Escape instead and the shapes stay waiting on the pill.
- “All at once”: nothing is asked. The shapes wait on the “Flip N shapes” pill, along with anything else you have drawn in that mode, until you press it. The pill's × discards every waiting shape, traced or drawn.
While they wait, traced shapes can be reshaped with Points and Curves: pull a point, delete a stray one, sharpen a corner the tracer missed.
Press “Trace” again and the new trace replaces the one still waiting. It never touches shapes you drew yourself, and never cuts that are already made. Flipping the batch is one step in the history, so one undo takes all of its cuts back together; shapes you choose to put back are placed at once, as a step of their own. Opening a project file throws away anything still waiting, since it belonged to the design being replaced.
If the settings leave nothing to trace, a message says so and suggests the “Threshold” or “Detail” sliders.
Why it works this way
A trace nearly always wants tidying. The tracer cannot know that a kink in a line is a flaw in the photo, or that two touching shapes were meant to be one; you can, and the waiting shapes give you the chance before any paper is cut.
Asking once for the whole batch is what makes a trace usable. A photo can easily give twenty regions, and twenty direction prompts one after another would be unbearable. It is also honest to what a trace is: one gesture, one decision, one undo.
The cyan fill, at about a third strength, is there because a thin outline is lost against a photo, and for the same reason waiting shapes are kept on top of both the photo and the sheet. Hiding the photo after the flip solves the opposite problem: a photo shown strongly over the sheet hides the very cuts that have just been made.
The metaphor
The waiting shapes are a proof. A compositor setting type by hand laid the lines in a galley, a metal tray, and a galley proof was pulled from it so the text could be read and corrected before anything went to press. Nothing on a proof was final, and that was its whole value.
They are also the Japanese woodblock's hanshita: the finished drawing on thin paper, pasted face down on the block for the carver to cut through. Traced shapes lie on the sheet the same way, exactly where the cut will go.
Both metaphors break in the same place. A hanshita was destroyed by the carving that used it, and a proof, once passed, led to the press and no further argument. Here the plan is cheap: discard it, trace again, reshape it, and even after the flip, undo.
A history
In art
Artists have always traced, and always stopped short of committing. Renaissance painters transferred full-size drawings, cartoons, to walls by pricking their lines with holes and dabbing charcoal dust through them, a method called pouncing, or spolvero. What reached the plaster was a line of dots: enough to place the design, loose enough to leave the painter deciding while painting.
The waiting shapes are the same kind of mark: a trace precise enough to place a cut, but not yet the cut itself. The artist's judgment comes between the two, which is where it has always been.
In printing
Printing split the work between hands, and every handover became a checkpoint. In the Japanese woodblock print, designer, carver and printer were separate trades, and the hanshita was the handover between the first two. In letterpress, the galley proof sat between compositor and press, and corrections were made there, where they were cheap, rather than on the press, where they were not.
“Flip” is the press. Before it, you are changing a plan; after it, you are changing paper.
In technology
Tracing from a photograph by hand has a long technical history. Max Fleischer invented the rotoscope in 1915 and patented it in 1917: film was projected frame by frame onto a glass panel, and an animator traced each frame onto paper, choosing as he went what to keep and what to leave out.
Autotracing software separated the trace from the commitment in the same way. When Illustrator gained Live Trace in 2005, a traced result kept a live link to the picture it came from, so its settings could be changed until it was expanded into ordinary paths. The waiting shapes are that stage here: a trace you can still change, before it becomes paper.
In professional software
Professional software is full of results that wait before they become final: a live trace, an adjustment layer, a sketch, a preview of the cut. Treat a trace here as a proposal to be checked, and you will be working the way those programs expect.
- Adobe Illustrator. An Image Trace stays live, linked to its image, and answers to every change in the ‘Image Trace’ panel. ‘Object › Image Trace › Expand’ commits it to ordinary paths, and ‘Object › Image Trace › Release’ throws the trace away and leaves the image.
- Adobe Photoshop. Adjustment layers and Smart Filters keep an edit open: the pixels beneath stay as they were until you merge or flatten the layers.
- Autodesk Fusion (formerly Fusion 360). A sketch is only a plan: nothing becomes solid until you extrude a profile, and the extrude dialog previews the result before you accept it. Each step is kept on the timeline along the bottom of the window, so you can go back and change the sketch later.
- Cricut Design Space. Its Prepare screen lays the project out on mats before anything is cut, and you can still move or hide pieces there.
- LightBurn. ‘Window › Preview’, ⌥P (Alt+P), draws every move the laser will make, cuts in black and travel in red, before you start the job.
What carries over. Look before you commit: check the plan while it can still change, and fix the plan rather than the material. The difference to watch is what you can edit at each stage. Studio Notan lets you reshape waiting shapes point by point; a live trace in Illustrator has to be expanded before its points can be moved, and once expanded it no longer answers to the trace settings.
Try this
- Set the flip mode to “All at once”, trace, and before flipping delete a stray point with Points. Then press the “Flip N shapes” pill.
- Trace, change the threshold, and trace again: the first trace is replaced, not added to.
- After a flip in “Each shape” mode, press the eye in the Trace panel to bring the photo back and compare the cuts with it.
Going further
See Flipping, Trace as and Undo and redo.
- Rebecca Salter, Japanese Woodblock Printing