What is a .3ds file? 3D Studio, missing textures, and the Mac

A binary file made of chunks

3DS is a binary file made of chunks. Each chunk starts with a two-byte number saying what it holds and a four-byte length, so a program that doesn't understand a chunk can skip it. The whole file is one main chunk, 4D4D. Inside are the editor part (3D3D) with meshes, materials, lights and cameras, and the keyframer part (B000) with animation.

Autodesk never published an official specification. Programs read the format from descriptions that circulated among developers; the best known is Jim Pitts's revision 0.91, edited by Paul Bourke in 1996. Libraries like lib3ds and Assimp are built on descriptions like these.

Is it a model, or a Nintendo 3DS game?

Game images for the Nintendo 3DS console use the .3ds extension too. Terminal tells you which one you have:

head -c 2 model.3ds

A 3D Studio file prints MM, because it starts with the bytes 4D 4D. For most such files, file model.3ds says 3D Studio model. No 3D program opens a Nintendo game.

Limits from the DOS era

3D Studio was made for DOS, and the format still carries its limits. According to the Okino converter:

• Triangles only. Polygons are split on export.
• At most 65,535 vertices and faces per mesh, because the counts are two-byte numbers. Larger objects are split into pieces. In a file converted from DXF that I have on my disk, one object is split into about 900 meshes, and the largest has exactly 65,535 vertices.
• Texture names in 8.3 form: eight characters, a dot and a three-character extension, as in DOS.
• Object, light and camera names up to 10 characters, material names up to 16. An old lunar module model on my disk has objects named group13 gr and a material called initialShadingGr – what's left of Maya's initialShadingGroup after 16 characters.
• No accurate normals, only smoothing groups the program rebuilds them from.
• No directional lights, and according to the Cinema 4D help, only one set of texture coordinates per point.

Why it opens without textures

Textures are never inside a .3ds file. The file remembers only the image names, and the program looks for them next to it. The lunar module model I have in a ZIP from 2008 is a good example. The file asks for TEXTURE_.TIF, TEXTUREA.TIF and BOOSTER3.TIF, but the same ZIP came with textures/booster3.png, texture_lem_flag.png and texture_lem_unitedstates.png. A different extension, a different folder, and long names cut to eight characters. No program finds them by itself.

Terminal lists the images the file expects:

strings model.3ds | grep -i -E '\.(tif|tga|jpg|png|bmp|gif)$'

Then convert or rename the images to the names on that list and put them next to the .3ds file. With long names you can only guess which image belongs to which shortened name, so try both ways.

Units and scale

3DS doesn't state a unit directly, but a file can carry a scale (master scale). Rhino offers to rescale the model on import based on it, and Assimp applies it straight away when reading. In the file converted from DXF, the numbers are 43 × 21 × 14 with a scale of 0.03937, and after loading they come out as 1097 × 529 × 355 – inches converted to millimetres. The lunar module model has no scale and measures 14 × 6 × 5 units, with nothing saying which. So check the size after opening and after converting.

Where 3DS came from

3D Studio for DOS came out in October 1990. It was written for Autodesk by a small company, the Yost Group: Gary Yost, Tom Hudson, Jack Powell and later Dan Silva. Hudson's roots go back to CAD-3D on the Atari. The .3ds format was the program's own format up to its fourth release. In 1996 it was replaced by 3D Studio MAX for Windows NT, where .3ds stayed on as an import and export format. 3D Studio MAX became today's 3ds Max.

How to open 3DS on a Mac

macOS doesn't know 3DS. On macOS 27.0.1 the system has no file type for it, the Model I/O framework doesn't load it, and neither Preview, Quick Look nor the Finder shows it. Autodesk's 3ds Max runs only on Windows.

• [Blender](https://extensions.blender.org/add-ons/autodesk-3ds-format/) is free and opens and saves 3DS through the "Autodesk 3D Studio (.3ds)" extension, with materials, textures, cameras, lights and animation. Up to version 4.1 it was part of Blender; from 4.2 you install it separately.
• [Rhino](https://docs.mcneel.com/rhino/8mac/help/en-us/fileio/3dstudio_3dsimportexport.htm) for Mac imports and exports 3DS, with lights, and with cameras as named views.
• 3DS Viewer on the Mac App Store costs $4.99, but its latest version is from January 2014.
• Preview3D, my app, opens .3ds files on a Mac in its window, in Quick Look and as Finder thumbnails. On iPad, iPhone and Apple Vision Pro too. So you can browse a whole folder of old models as thumbnails without installing Blender.

Preview3D reads 3DS through the Assimp library. It shows the geometry in one plain colour: it doesn't use the file's materials or textures, and it doesn't play animation. It applies the file's scale, as described above. Model info has the dimensions and the triangle count, plus a mesh check. On iPad and iPhone it stands the model on your desk in AR, fitted to the desk.

Converting 3DS to STL

On a Mac, Preview3D converts from File → Export model as… (⌥⌘E) to STL, OBJ or PLY, without uploading anything. Materials, textures, cameras, lights and animation are dropped. Models from games and visualisations are often built from many separate parts and need repairs before printing; the mesh check shows holes and edges that don't hold together. Then check the dimensions in the slicer.

Common questions

What is a .3ds file?

A model in the format of 3D Studio for DOS from 1990: triangle meshes, materials, cameras, lights and simple animation.

Why did my .3ds model open without textures?

The textures are separate images next to the file, and their names are at most eight characters long. The strings command shows which images the file expects. Name them the same and put them next to it.

Is my .3ds a 3D model or a Nintendo 3DS game?

head -c 2 model.3ds prints MM for a 3D model. Anything else means it isn't a 3D Studio model.

Does a Mac open .3ds without another app?

No. macOS 27 has no file type for 3DS, and neither Preview nor Quick Look shows it.

How do I convert 3DS to STL?

On a Mac, in Preview3D with File → Export model as…, or in Blender with the 3DS extension. Then check the mesh and the dimensions.

Why did a large model fall apart into many pieces?

One mesh in 3DS holds at most 65,535 vertices, so the exporter splits larger objects into pieces.

Related pages

• The .fbx file – 3DS's successor for moving scenes out of 3ds Max
• The .obj file – another old mesh format, with materials in an .mtl file
• The .stl file – the printing format 3DS is converted to

Sources

• Paul Bourke: the 3D Studio (.3ds) format – chunks, byte order, revision 0.91
• Okino: exporting to 3DS – the format's limits
• PRONOM: 3D Studio – the 4D 4D signature
• CGPress: the history of 3D Studio, an interview with Tom Hudson
• Rhino for Mac: 3DS import and export
• Cinema 4D: 3D Studio export
• Blender: the Autodesk 3D Studio extension
• Assimp: reading 3DS – scale, animation
• Mac App Store: 3DS Viewer

Have an old collection of .3ds models from a CD or an archive that won't open on your Mac? Write to me at apps@xfanta.com and tell me where it came from.