Trace a photo: Trace a photo · Studio Notan Learning Hub

Trace a photo lays a photograph over your sheet as a guide, then turns its dark and light areas, or two families of color, into shapes you can cut and flip. It is the oldest trick in the studio done by other means: put what you want to draw under something you can see through, and follow it. The difference is that here you set a rule once, and every pixel is judged by it.

What it does

With no photo, the Trace tab of the inspector shows a card, Choose a photo to trace. There are several ways in:

Choose photo on the card (or a click anywhere else on it) opens the file picker. File → “Trace a photo…” opens the same one.
Drop an image on the card, or straight onto the canvas.
Paste an image anywhere, except while you are typing in a field.

The card asks for JPG, PNG or WebP up to 50 MB; a larger file is refused before anything is decoded. The photo is turned the right way up from the orientation the camera wrote into the file. If its longest side is over 2,048 pixels it is decoded straight down to that size, and the panel says so (“Resized from 8064 × 6048 to 2048 × 1536”, for instance). A smaller photo is used as it is, never enlarged. It arrives fitted inside the sheet, and the inspector turns to the Trace tab.

From there the work runs down the panel, roughly in this order:

Place it. Fit, Fill, Move photo and Crop set where it lies; Skew straightens a photo taken at an angle.
Choose how to split it. Separate by Brightness (dark is front) or Color (nearness to colors you pick).
Adjust against a preview. Tone, the histogram and its levels, Threshold, Blur and Detail, watching Photo, Adjusted, Two-tone or Outlines over the sheet.
Shape the outline. Smoothness, Corner angle and Corner span, and Trace as one shape or several.
Trace. The shapes arrive waiting above the photo, filled in cyan. You can reshape them with Points and Curves, and flipping makes them cuts. Tracing again replaces a trace that is still waiting, never anything you drew.

The eye beside the heading hides and shows the photo; the bin removes it. Reset, at the foot of the panel, puts every adjustment back to its default but keeps the colors you picked.

The photo is never part of the design. It stays out of undo, autosave, exports, shares and cloud saves, and goes into a project file only if you choose File → “Save project with photo”. This browser keeps its own copy, with the photo's place and settings, so it is still there after a reload until you remove it.

Why it works this way

A photo is heavy, private and not the point. Kept in the undo history, a photo of a few megabytes would be copied into every step; kept in the design, it would leak into every export built from it. Nothing about it needs to leave your browser, so nothing does. Even the resizing happens on your own machine.

The 2,048-pixel limit is about phones as much as quality. A 48-megapixel phone photo is roughly 195 MB of pixels once decoded, enough on its own to make a phone's browser close the tab. So the app reads the size from the first bytes of the file and, where the browser allows, decodes straight to the working size, so the full image is never held in memory. On a sheet a few inches across, one of those pixels is a fraction of a millimeter, finer than a knife can follow. The live previews run on a 1,024-pixel copy so that the sliders answer at once; Trace repeats the same settings at the full working size.

A trace lands as waiting shapes rather than cuts because a trace nearly always needs tidying, and a waiting shape is easier to throw away than a cut is to undo. And whichever way you separate, the pipeline makes one decision per pixel, front or back, from a single gray “score” image. That is why the histogram, levels, threshold and Detail behave the same in both modes: you learn them once.

The metaphor

The metaphor is tracing paper on a light box. The photo lies underneath, the sheet is the paper you see it through, and Opacity is how thick that paper is. Like tracing, it asks you to decide what matters and leave out the rest.

It also borrows from the camera lucida, the prism that lays a view over your drawing so that eye and hand see one image.

The metaphor breaks over who makes the judgments. A hand tracing a face makes a thousand small decisions on the way: this shadow is a shape, that one is only light. Here the judgment is made once, as a rule (darker than this, or nearer this color), and applied to every pixel without favor. The machine traces a shadow as faithfully as a nose. That is why so much of the panel is about shaping the rule before you trace, and why the result waits for your hand afterwards.

A history

In art

Tracing is as old as workshops, and has always been a little awkward to admit to. Cennino Cennini's handbook for painters, written around 1400, gives recipes for tracing paper. One is a kid parchment scraped until it barely holds together, which turns transparent by itself and can be made clearer still with linseed oil. Its purpose was plain: to carry a good figure or ornament from one work into the next.

For walls, Renaissance painters drew a full-size cartoon, pricked its lines with rows of tiny holes, held it to the plaster and dabbed it with a bag of charcoal dust. The dust passed through the holes and left a dotted outline: spolvero, or pouncing. It became a workhorse of fresco in the fifteenth century, because wet plaster gave the painter a single day on each patch and no time to redraw it freehand.

In 1806 William Hyde Wollaston patented the camera lucida, a prism on a stand that lays the scene over your paper. In October 1833, on his honeymoon, William Henry Fox Talbot sat by Lake Como with one and was dissatisfied with what his pencil made of it. That frustration set him wondering how the image might fix itself on paper, and led to his work on photography. Tracing did not only come to use photography; it helped to cause it.

The painter David Hockney argued in Secret Knowledge (2001) that lenses and mirrors were used by painters earlier and more widely than art history had allowed. The argument is still disputed, which says something about how charged the idea of tracing remains.

In printing

In the Japanese woodblock print, the artist's drawing was copied onto very thin paper, pasted face down on the block, and the carver cut straight through it, leaving the lines standing in relief. The drawing was destroyed in the making; what survived was its trace in wood. The cut followed the paper exactly, which is the relation between a traced shape and a cut here.

Photomechanical printing made tracing industrial. Printers sorted artwork into line copy, which is pure black and white, and continuous tone, which had to be broken into a halftone screen. Line copy was photographed on very high-contrast film, so every tone went either to black or to clear: a two-tone split of a drawing, made by chemistry instead of a slider. The Two-tone preview is that negative.

In technology

Max Fleischer applied in 1915 for a patent on the rotoscope, granted in 1917: a projector that threw one frame of live-action film at a time onto a drawing surface, so that an animator could trace real movement.

Tracing by computer, or autotracing, grew up with desktop publishing. Adobe sold it as a separate program, Streamline, then built the idea into Illustrator as Live Trace (CS2, 2005) and replaced that with Image Trace (CS6, 2012). Peter Selinger's Potrace, first released in 2001, became the free standard, but it is licensed under the GPL, and using it would have put this whole app under that license. So Studio Notan traces with its own pipeline: a score image, levels and blur, a threshold, Detail to drop specks and fill pinholes, an outline that runs along the cracks between pixels, then smoothing, corners and curve fitting.

In professional software

Turning a photo into shapes is called image tracing, autotracing or vectorizing: a raster image, made of pixels, becomes vector paths. The programs that do it work the way Studio Notan does: you set a rule, the program applies it to every pixel, and you tidy the paths afterwards.

Adobe Illustrator. Place the photo, select it and open ‘Window › Image Trace’. Choose a preset such as ‘Black and White Logo’ or ‘Silhouettes’, or set the Mode and Threshold yourself. The result stays tied to the photo and can be retuned until you choose ‘Object › Image Trace › Expand’, which turns it into ordinary paths.
Inkscape. ‘Path › Trace Bitmap’ does the same job for free. The traced paths land exactly on top of the photo, so drag them aside to compare the two.
Autodesk Fusion (formerly Fusion 360). ‘Insert › Canvas’ lays a photo on a plane or a face as a reference. Tracing there is done by hand: you calibrate the canvas to a known size, then draw over it with sketch lines and splines.
Autodesk AutoCAD. ATTACH brings a photo into a drawing, and drafters trace it by hand with PLINE or SPLINE. The Raster Design toolset adds automatic conversion to lines and polylines, but only from a two-tone image, so a photo has to be split first, just as it is here.
Silhouette Studio. Its Trace panel asks you to select a trace area, then shades in yellow what will be traced as you move the Threshold slider. ‘Trace’, ‘Trace Outer Edge’ and ‘Trace and Detach’ make cut lines in different ways.
LightBurn. ‘Tools › Trace Image’ turns a photo into vectors for a laser, with Cutoff and Threshold setting which band of grays is traced. The photo is kept underneath unless you ask for it to be deleted.

What carries over. Judge the split before you trace, and treat the first trace as a draft to tidy, not a result. One pitfall: in Illustrator’s Black and White mode, tick ‘Ignore White’ under ‘Advanced’, or the paper is traced as white shapes along with the dark ones. Studio Notan only ever makes the front shapes.

Try this

Photograph a leaf on white paper. Bring it in, switch Preview to Two-tone and press Trace. Then look at Outlines before you trace again, and compare.
Bring in a portrait and look at it under each Preview in turn. Notice where the face's own shadows run into the background: that is where the rule needs your help.

Going further

Cennino Cennini, The Craftsman's Handbook. Carmen C. Bambach, Drawing and Painting in the Italian Renaissance Workshop. David Hockney, Secret Knowledge. Philip Steadman, Vermeer's Camera.