Jernej LeticaPhotography Tools & Stories
Photo Printing

Image to Lithophane STL: size the download

Make a binary STL from an image with a flat back and closed sides. Check the dimensions, sampling grid, triangle count and download size before saving.

Built and written by Jernej Letica

Local browser processing · No upload · No account required

JPG, PNG, WebP, HEIC or AVIF. Flat rectangles only. The width includes the frame; frame height is its thickness.

Choose a photo to begin.

Mesh limit: at most 40,000 grid cells and 400 cells on either side. Photos are reduced to a preview up to 1,600 pixels on its longest side; the output uses that preview.

Size, triangles and file size appear here before saving.

How to convert an image to a lithophane STL

  1. Choose an image and crop the area you want to print. The output is a flat rectangle, so decide its proportions before entering the physical width.
  2. Enter width and thickness in millimetres. I check the frame height too, because it is measured from the back and must stay within the same thickness range.
  3. Read the triangle count and exact byte count under the preview. Reduce resolution if you prefer a smaller mesh, or keep the automatic cap when a large panel reaches it.
  4. Download the binary STL and import it as millimetres. Confirm the bounding dimensions and inspect the sliced paths before choosing the printer profile and orientation.

I separate file checks from printing claims

I can check that a saved STL has a consistent triangle count, outward faces and a closed surface. That is what the mesh tests on this tool cover. A valid file still needs the right slicer settings and a suitable material, so I do not present those checks as a successful print.

I have not printed these outputs. My aim here is to make the file predictable before you save it: its size is visible, its coordinates are in millimetres, and its back is part of the same mesh as the photographed surface.

A small binary STL calculation

The mesh test generates the following small square grid. Each triangle occupies 50 bytes and the binary header plus count occupies 84 bytes; these are the layout used by the writer and parser.

GridTrianglesComplete file
2 × 2 cells321,684 bytes
4 × 4 cells964,884 bytes

What the STL actually contains

A lithophane represents a photograph through material thickness. Dark areas rise farther from the flat back than light areas. The STL stores that shape as triangles, together with the back surface and the edge walls. It does not contain the original photograph, a light source or a printer instruction file.

This download is binary STL. The header is followed by a triangle count and fixed length triangle records. Each record has a normal and the corner coordinates. The file size displayed before downloading comes from the same grid dimensions used to build the mesh, so you can assess the download without waiting for a full export.

Import the dimensions in millimetres

STL has no built in unit label. This tool writes the width, height and thickness as millimetre coordinates. Select that unit when your slicer asks. Scaling a model after import changes thickness as well as the picture size, which also changes how light can pass through it.

The width includes any frame, and the height is calculated from the crop. Frame height is measured along the thickness axis. Maximum thickness is an upper endpoint for the photo, so an image without a black region may not reach it. The default border uses that endpoint, making the outside frame the thickest part unless you change it.

A closed mesh with a bounded download

The front and back share matching edge subdivisions with the side walls. This keeps the perimeter closed rather than leaving an open sheet for the slicer to repair. The mesh tests count every undirected edge and require it to belong to a pair of triangles. They also compare stored normals with winding and check that signed volume is positive.

Resolution requests are bounded by the mesh limit. The largest allowed grid has 40,000 cells, with a separate limit of 400 along either side. The source preview is also reduced before sampling. The report states the actual grid, and worker processing lets the controls remain available while the binary file is being assembled.

Tips for better results

  • I check the imported width before rotating or arranging the model on the build plate.
  • Keep the STL and the original image separately if you want to revisit the crop later.
  • Inspect the sliced interior as well as the outer surface; an attractive solid preview alone does not show the toolpaths.

Privacy

Your photo is processed in your browser and never leaves your device. No upload or account is needed to create the STL.

Frequently asked questions

Is the download binary or ASCII STL?

The maker writes binary STL with an explicit triangle count. The download size includes the header and every triangle record. This is a geometry file for a slicer, rather than G-code ready to send straight to a printer.

What units should I choose in the slicer?

Choose millimetres. The coordinates use the physical width and calculated height displayed by the tool. STL cannot enforce a unit choice, so check the imported dimensions before accepting any automatic scaling offered by your slicer.

Does the STL include a closed back?

Yes. It has a flat back, a variable thickness front and side walls that close the perimeter. The photo is not exported as a single open surface, and you do not need to add a backing solid to close it.

Why does the triangle count change with resolution?

A denser grid divides the same area into more surface triangles. Both front and back use that grid and the sides follow its perimeter. The count stops growing when the requested sampling reaches the mesh limit.

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