The photo you trace from is a guide, never part of the design. It stays out of everything the design goes into, and it is kept in only two places: in this browser, until you remove it, and in a project file, when you ask for that by name.
What it does
The photo is never in:
- the undo history;
- the design's autosave;
- any export, of the artwork or of the cut lines;
- a share link, or the picture that goes with one;
- a cloud save;
- the app's session recording, which pauses while a photo is loaded and starts again once you remove it.
This browser keeps it. When a photo arrives, a copy is stored in a database of its own in this browser, apart from the design's autosave: a JPEG of the working copy, at most 2048 pixels on its long side, at 90% quality. Its place, crop, skew, trace settings and preview are saved beside it within half a second of each change. So after a reload the photo is still there, in place and set up as you left it. Its place is kept relative to the center of the sheet, so a different window size still finds it on the sheet. It stays until you press the bin in the Trace panel's heading, “Remove the photo”, which clears the photo and its settings together. It is not in any other browser or on any other device.
A project file keeps it when you ask. While a photo is loaded, the File menu offers “Save project with photo”: the design, as “Save project” saves it, plus the photo and its place, crop, skew, settings and preview. “Open project…” on that file brings the photo back as it was, and from then on this browser keeps it again. Open accepts a photo only if it is a clean JPEG, carried in the file as a data URL, under 8 MB. Autosave and the server never take a photo.
Because the kept copy is drawn afresh from the working image and encoded anew, it carries none of the original file's metadata: no camera, no date, no location.
Why it works this way
Three reasons, in order of weight.
Privacy. Photos are personal: faces, homes, children, documents. A design is shared, saved to the cloud, exported and sent around; if the photo rode along, it would go wherever the design went, usually without anyone thinking about it. Keeping it out by default means the photo leaves your machine only through a command with the word “photo” in its name.
Size. A design of a few hundred cuts is tens of kilobytes. A photo is megabytes. Share links, cloud saves and autosaves stay small and quick because they hold only the design.
Meaning. The design is the cut paper. The photo is scaffolding, and scaffolding comes down when the building stands. Undo steps through your design, not through the photo's adjustments, and an export is the work, not the reference you worked from.
The metaphor
The photo is non-photo blue. Illustrators and layout artists sketched and ruled guidelines in a pale blue that the graphic-arts camera could not see: its film, blind to red and very sensitive to blue, recorded the pale blue as if it were white paper. The sketch stayed on the board and vanished from the print. Designers placing photographs in a layout did something similar with rough stand-ins marked FPO, “for position only”, which were swapped for the real pictures before anything went to press.
The metaphor holds for the essential point: a guide present while you work and absent from what is reproduced. It breaks in a way that makes this guide safer. Non-photo blue is on the artwork, and a careless exposure could still pick it up. Here the photo is never on the artwork at all. It lives in a layer of its own on screen and a store of its own in the browser, and nothing that saves, exports or shares the design ever reads it.
A history
In art
Guides that disappear are as old as painting. Beneath many old paintings lies an underdrawing, laid on the ground to place the composition and then covered by paint; infrared imaging now lets conservators see it again, changes of mind and all.
Optical guides came later. William Hyde Wollaston patented the camera lucida in 1806, a prism that lays the image of a scene over the drawing paper so that the hand can follow it. William Henry Fox Talbot tried one in Italy in 1833, was disappointed with his drawings, and set out instead to make the image fix itself on paper, one of the paths that led to photography. David Hockney's 2001 book Secret Knowledge argued that earlier masters used such devices far more than was admitted; the claim is still argued over. Either way, the guide was never the picture.
In printing
Reproduction depended on keeping guides out of the plate. Non-photo blue let an artist sketch, rule and annotate on the very board that would be photographed, knowing the camera would ignore it, and layout artists wrote their notes to the printer in it. For photographs, the FPO print showed where a picture would go and how it was cropped, while the real one traveled separately to be reproduced at full quality. The separation of guide from artwork was a working habit of the trade long before it became a rule in an app.
In technology
The pieces that let a browser keep a photo, and a file carry one, are all standards. JPEG, published by the Joint Photographic Experts Group in 1992, compresses a photo by discarding detail the eye is unlikely to miss; at 90% quality the loss is slight. A camera's details and location travel beside the picture in a separate block of metadata, Exif, which is why a fresh encoding leaves them behind.
The data URL, defined in 1998 in RFC 2397, lets a file carry an image inline as text, at the cost of about a third more size; that is how a project file holds its photo. And IndexedDB, a W3C Recommendation since 2015, gives each website a private database in the browser, readable by that site alone, which is where this app keeps the photo between visits.
In professional software
Most professional programs make the same choice about the pictures they use: keep a copy inside the document, or keep only a link to the file on disk. Adobe calls these embedded and linked images; AutoCAD calls the linked kind an external reference.
- Adobe Illustrator. In the ‘File › Place’ dialog, the ‘Link’ checkbox decides: ticked, the document stores only a path to the image; cleared, it stores a copy. The ‘Links’ panel lists every placed image and can embed or unembed one, and ‘File › Package’ gathers the document, its linked images and its fonts into one folder.
- Adobe Photoshop. ‘File › Place Embedded’ copies an image into the document as a Smart Object, and ‘File › Place Linked’ leaves it as a separate file. ‘Layer › Smart Objects › Embed Linked’ brings a linked file inside, and ‘File › Package’ collects linked files beside a copy of the document.
- Adobe InDesign. Placed images are linked, and the ‘Links’ panel warns when one is missing or has changed. ‘File › Package’ is the usual last step before a layout goes to print, copying the document, its links and its fonts into one folder.
- Autodesk AutoCAD. An image attached with
ATTACHis an external reference: the drawing stores only its path, and the ‘External References’ palette shows whether each file can be found.ETRANSMITbundles a drawing with its references, ready to send. - Autodesk Fusion (formerly Fusion 360). A photo inserted with ‘Insert › Canvas’ is stored in the design, to sketch over, and can be hidden without being deleted.
What carries over. Know where a reference image lives before you send a file to anyone. A link keeps the document small but breaks when the photo moves; an embedded copy goes everywhere the document goes, which for a personal photo may be further than you meant. Studio Notan takes the cautious default: the photo stays out of every export and share link, and goes into a project file only when you choose to save the project with the photo.
Try this
- Load a photo and reload the page: it comes back where you left it, with its settings.
- Choose “Save project with photo”, press “Remove the photo”, then open the file with “Open project…”. Photo, place and settings return together.
- Export the artwork with a photo loaded, and open the export: there is no photo in it.
Going further
See Trace a photo, File and Share.
- Richard Benson, The Printed Picture
- David Hockney, Secret Knowledge