ARTICLE

3D photogrammetry: turning photographs into 3D models

Discover how Canon EOS cameras are being used to create lifelike 3D models for video games, movies, manufacturing and art.
A technician on a step-ladder adjusts one of a large number of lights and camera arrays positioned in a circle around a flat scissor lift.

3D scanning service company Sample & Hold focuses on 3D photogrammetry for the arts and creative industries. "That's anything from products for advertising, to people for computer games and TV or film, to sculptures for sculptors who want to 3D-scan models and maquettes and then produce larger versions using a 3D printer or CNC machine before applying a layer of clay," explains Sample & Hold co-founder Sam Jackson.

3D photogrammetry is the process of reproducing a physical item in order to make an accurate 3D model. It can be used to capture everything from people and historical artefacts to aircraft, buildings and even larger structures.

"It's a very good way of making an object tangible and immersive, so you can look around it and see the texture of it," says John Maurice, European Product Marketing Manager at Canon Europe. "You can also do this in a CG render, but it's not the same because you never get all the nuances that photogrammetry captures."

The applications of digital photogrammetry and 3D modelling are endless, with the technique employed as a solution in manufacturing, engineering, design, entertainment and healthcare. "Creating 3D models of somebody can help with a diagnosis and the monitoring of treatment," explains John. "And if you work in industry, being able to make a 3D model cuts down on the expensive prototyping stage."
A general view of a large number of lights and camera arrays positioned in a circle around a flat scissor lift.

For its full-body photogrammetry rig, Sample & Hold uses 154 cameras. "The beauty of doing it this way is that you're capturing everything instantly using flash," says Sam. "So you can capture people and other animated subjects moving during the scanning process."

A man in t-shirt and trousers stands on a scissor lift in the middle of a circle of lights and camera arrays.

A scissor lift is used to adjust people's height within the centre of the full-body photogrammetry camera array. "We have redundancy built-in," says Sam. "It's designed to scan somewhere around two metres high, so if someone's shorter, we'll pump them up to the point where their head is inside the correct capture area and the lower cameras won't be used."

3D photogrammetry is a very specialised field and the process is a meticulous one. "You need to take lots of pictures of the subject, and typically there needs to be a two-thirds overlap between the images in order to create the 3D map," John says. "So, if you're taking the shots with a single camera, you need to move it slightly but very precisely, so that you get that overlap."
It's for this reason that 3D photogrammetry companies tend to use rigs fitted with multiple cameras. The cameras are positioned so as to capture the subject from every angle in one hit. All the images then feed into specialist software which compares the overlap and derives the 3D geometry.

Leading 3D scanning specialist Sample & Hold uses two such rigs: one for body scanning and the other for head scanning. "We've got 154 cameras in our body rig," says Sam Jackson, one of the company founders. "While that's not a huge rig, it's still a significant number of cameras. They're positioned in a full 360° arrangement around the person and fire simultaneously, so we end up with a load of images of that moment in time, which we can then push through Reality Capture software. That takes all of that information in those images and finds all the same points that it can in each image and basically creates a 360° model out of it."
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Some of the lighting rigs and camera arrays in a 3D photogrammetry studio setup.

"We build our own lighting units because there's nothing to really do it off-the-shelf," says Nick Foots of Esper, which provides multi-camera and 3D scanning equipment. "It can be polarised or non-polarised light, which allows you to extract different levels of detail from the surface." Sometimes it isn't just light that's required, adds Sam Jackson of Sample & Hold, which uses Esper equipment in its own rigs (shown here). "If the subject has a single plane or surface which is one uniform colour, photogrammetry doesn't really work without some form of a pattern projected onto it to help to key it," he explains.

A technician adjusts one of the Canon cameras in a tall camera array.

The multi-camera arrays at Sample & Hold enable the company to capture objects as small as a coin and as large as a three-metre square.

Which is the best camera for 3D photogrammetry scanning?

Choosing affordable cameras is a priority when you're looking to populate a 3D photogrammetry rig with 100-plus bodies. "Entry-level DSLRs are good for this type of work," says John. "And affordable lenses, too. 50mm lenses are popular, because they're cost effective and good quality."
One of the benefits of choosing Canon EOS cameras for 3D photogrammetry is the extensive system support that's available. "There's a whole portfolio of products at different price points," says John. "If you need accessories such as AC adapters, we can provide those. And we can provide the Canon SDK [Software Development Kit] to open up the Canon camera hardware to third parties so that it can be integrated into a specialist workflow. And then, when you upgrade cameras, it's just a case of upgrading the SDK to support the new product, so your workflow isn't disrupted."

Sam explains that 3D photogrammetry doesn't demand the top-spec features found only in professional cameras. "We currently use the entry-level Canon EOS 2000D and the Canon EOS M6 Mark II," he reveals. "The EOS 2000D has a 24MP sensor, which is nice and high, and it's really good value. It's a similar story with the EOS M6 Mark II, although that is 32.5MP. That camera was a bit of an experiment for us, actually, because we hadn't used mirrorless before. Now we're thinking about fitting out all our rigs with EOS M6 Mark IIs because they're excellent cameras.
In a studio, a Canon EOS camera on a tripod faces a glass table with a single red trainer on it. A man is viewing the image of the shoe in software on his monitor.

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"Part of the reason why we haven't moved to full-frame is that the depth of field is greater with all the APS-C cameras, and that's really critical to the processing of the data."
A close-up of a Canon EOS 1300D camera on a rig in a 3D photogrammetry studio.

As well as using Canon EOS 2000D and EOS M6 Mark II cameras, Sample & Hold's multi-camera arrays also make use of older cameras from their early rigs (such as the Canon EOS 100D and EOS 1300D) for things like capturing the back of a subject's head.

A technician sits at a laptop while a man stands within the 3D photogrammetry array in the background.

Canon's SDK (Software Development Kit) enables selected Canon cameras to be controlled remotely via third-party software. A non-Canon open source control SDK that runs on Linux is also available, John notes.

In its full-body rig, Sample & Hold uses a mix of 100mm, 85mm and 50mm lenses such as the Canon EF 85mm f/1.8 USM and the Canon EF 50mm f/1.8 STM, with the longer focal lengths used for picking out important areas such as the feet and the hands. The head rig uses a combination of 40mm and 50mm lenses, such as the Canon EF 40mm f/2.8 STM.

"We'll always stick with prime lenses," says Sam, "partly because there's no worry that things are going to shift, especially if we're moving the rig.

"Entry-level cameras aren't designed to do what we're doing with them, so there can be discrepancies in the shutter timings," he continues. "To get around this, we use flash to control the exposures. We work in a dark room and run our cameras at 1/3 or 1/5 sec shutter speed, and the flashes all fire simultaneously to expose the images. We control the cameras using Smart Shooter software, and sync everything using Esper TriggerBoxes."
A laptop with a 3D model on its screen of a standing figure surrounded by representations of cameras.

The images captured by all the cameras in the array are brought together in specialist software, which collates them all and constructs a 3D model from all the data.

Using multiple cameras to make a photogrammetry scan

Esper provides multi-camera and 3D scanning solutions to service providers in the video game and visual effects industries, as well as for advertising, academic research, bullet-time photography booths and beyond. Company director Nick Foots says that the most important thing to consider when setting up a 3D photogrammetry system is the final output.

"It's the first question I ask anybody during a consultancy call: what is your end use? As in, what resolution and format? And then you can work back through the whole pipeline based on that," Nick explains. "So, if something's only ever going to be used for e-commerce on the web at a not particularly high resolution, then, dare I say it, there's no point in having 60 cameras pointing at the thing.

"If you're going to do a 4K video game, then you may need upwards of 160 cameras, but if you're going to create 'mini-me' 3D models of people using an FDM printer, then you're really only going to need 30 to 50 cameras. There's just no way a 3D printer is going to replicate the resolution that you're going to get from using any more than that.
Two men sit at a table looking at a laptop screen showing 3D models of human figures.

Sam says the biggest challenge when it comes to photogrammetry is trying to capture certain materials. "Take trainers as an example. Fashionable trainers tend to be made of lots of different materials that are black or shiny or transparent or have a glitter effect, and all of those things are problematic for the capture process." By comparison, the human figure is relatively routine.

"If an object's small enough and it doesn't move, you can probably do it quite economically with three or four cameras on an arc, a bit of controlled lighting and a turntable that you move by hand," Nick continues. "You can also do perfectly good photogrammetry scans with a single camera, although you'll need to consider if that's scalable for what you want to do, and how it's going to fit into the whole workflow."

Starting with a single camera is something that Sam at Sample & Hold recommends. "Anyone can have a go at photogrammetry out in the field, using daylight and a single camera," he says. "With a subject that's not going to change or move, such as a house, you don't need to use multiple cameras, you just use one camera from multiple positions.

"There are lots of tutorials on YouTube that show you how to do it," Sam concludes. "And then you can run the images through something like Meshroom, which is a free, open source bit of software, and produce 3D models. You can create some really cool stuff this way."

Skrivet av Marcus Hawkins


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