How Does 123D Catch Do It?

123D Catch works by reading the pixels that make up a digital photograph: the tiny dots of red, green, and blue.

As the photographer moves around an object to collect different views, Catch assigns each pixel in the image a unique code, such as R-40, B-578, G-564, and so on. The app stores the codes for those pixels that comprise the object, and deletes the codes that it applies to pixels in the background.

Catch works best with the 123D Catch mobile app, because the cameras built into mobile devices tend to have great “depth of field.”

Depth of field is a photography term that refers to how much of what’s in a camera’s field of view is in focus, both in the foreground and deep into the background. Depth of field is important with Catch because you want your entire object to be in focus no matter how close or far apart it is from the camera lens.

However, there is a desktop version of Catch, called Memento, that allows you to stitch together photographs, or scans of photographs, taken with a nonnetworked camera, such as a digital SLR. The advantage of using these types of images is that digital SLR cameras can usually take higher-resolution photographs than mobile devices, which in turn means that you will get a cleaner 3D model requiring less clean-up work.

As this book goes to print, Memento is available in beta for the Windows platform, with a Mac version upcoming. Autodesk also offers a pro version of Catch called Re-Cap. You can find both of these programs through Autodesk.com

While catching 3D images of objects is neat, there are particularly innovative applications of the technology that involve fitting manufactured objects to organic objects, such as human bodies. This opens a new world of design potential for jewelry, fashion, and prosthetics: instead of playing a guessing game to make objects that fit a large number of people, 3D capture allows designers to create customized solutions for individual end users that fit more comfortably.

To see this in action, check out Dutch designer and maker Anouk Wipprecht’s Faraday Dress. Wipprecht created a 3D scan of her own body with 123D Catch, and then laid out the 94 panels for her dress, as well as unique shoulder pieces, using two other apps: Autodesk Maya and 123D Make.

The end result was electrifying: a high-fashion Faraday cage (Figure 6-4) that allowed Wipprecht to stand between two Tesla coils and safely intersect with bolts of high-voltage electricity.

Figure 6-4. Anouk Wipprecht in her Faraday Dress (photo by Kyle Cothern)

Scanning with Catch: The Basics

Although 123D Catch is a free, easy-to-use app, there are several basic steps and techniques to keep in mind when scanning in an object that will help you achieve expert-level results.

Let’s take a look at some tips and tricks:

Have a solid plan for your photo shoot

Do a practice run to figure out how to get all the way around your object, while keeping it roughly in the same space in your camera’s frame.

To get the best result, we recommend doing a test run and marking the spots on the floor that you want to hit for the final capture.

Remember: The object does not move

You do. The way photogrammetry works is that it reads pixel data. It matches up the pixels that read the same from shot to shot, and deletes the data that changes drastically.

For instance, if you are using Catch to capture a 3D model of a person in a room, the software’s algorithm would read small details—things like an eye, or a freckle on the person’s cheek—and use them as anchor points. When you move about 15 degrees to take the next shot, the software will look for and read those same anchor points. It will then delete all the parts of the image that are in the background and out of focus.

Figure 6-5. Image by Instructables user damonite

Fill the frame

Catch gets the best results when you fill the frame nearly edge to edge with the object, and then keep the object in that frame as you move around it (Figure 6-6).

Figure 6-6. The dinosaur you wish to scan

Move in a slight upward spiral or two loops

As you circle the object, move the camera in a slight upward swirl or spiral (Figure 6-7). Using Catch is like a dance: it’s OK to take practice shots to find the rhythm and footwork that get the best results.

The app version will prompt you to take a bottom loop then a top loop. You will want to make sure that you are shooting at a slightly upward angle when doing the bottom loop and a downward angle when doing the top. The blue highlighted bar will tell you if you are lined up at the correct angle around the object.

Figure 6-7. Image by Instructables user damonite

Catch works best with ambient lighting and a busy background

No need to have an all-white photo booth and careful lighting to get great results. In fact, Catch works best with ambient and low-contrast lighting, such as that found on a cloudy day. It’s also good to have a lot of detail in the background, so that Catch can tell which pixels to keep and which to throw away.

Because of the way the software works, a great environment in which to do a capture run would be a room with newspaper pages covering the walls, because they would create a varied background that the app could easily distinguish from the object you want it to focus on.

Dont forget the undercuts

Although it is now easier than ever to clean up scanned models when they have the occasional hole, the entire reason that you are scanning something is to get as much accurate data in the first place as possible. So if your object has some extreme undercuts, make sure you shoot the image from a vantage point that grabs those babies (Figure 6-8).

Figure 6-8. Undercuts shown in white

No hard shadows, no shiny edges

Because things like hard shadows and highlights move as you move, they typically don’t work well for 3D scanning. If your object is naturally shiny, try applying a fine spray powder, such as the kind sold for foot odor. This will dull the object’s finish so that you can capture a good scan, and it’s easy to remove afterward (Figure 6-9).

Figure 6-9. The results of shiny edges

Let’s Take Some Photos!

Now that you understand what Catch does, and how to use your camera to obtain the best results, let’s put that knowledge into action and capture some data.

Step 1: Make a Practice Run

If your object is portable, set it up in a way that you can comfortably walk all the way around it. If not, be sure you that you can create a safe area to get around the object. Be sure to watch for people and vehicle traffic if you are shooting in a busy outdoor location (Figure 6-10).

Figure 6-10. Clear a path before starting to shoot

Holding your camera up and using the viewfinder, walk around the object once to make sure there are no literal stumbling blocks like walls or rocks that would stop you from a successful capture. Doing this before you make your scan helps reduce the need to make major adjustments to the object mid-shooting, which can complicate the creation of an accurate scan (Figure 6-11).

Figure 6-11. Walk around your object

Step 2: Check and Correct Lighting

Now check the lighting. It should be ambient and diffused, allowing you to see all the details of your object while creating no high-contrast shadows or highlights. The perfect scenario is an overcast day (Figure 6-12); this makes bright light without creating highlights. See if you can replicate this if you are in an indoor environment.

Figure 6-12. Perfect lighting for a great capture

Step 3: Capture the Object

If you are using the app version of Catch to create your photos, open that now. Swipe left to start a new capture (Figure 6-13).

Figure 6-13. The Start a New Capture button in the iPhone app

If you’re using a handheld camera: while looking through your camera’s viewfinder, move closer to or farther from your object as needed, until it fills but does not overlap the frame.

Begin to move around the object slowly. As you slide to the next shot, keep the details from the previous shot still in the frame. You want to take a new photograph for every 15 degrees of movement (Figure 6-14).

Figure 6-14. Seeing the path around the object

Step 4: Prepare Your Shoot

At this point, you need to prepare your shot (don’t shoot until the next step). Find your start point, usually the focal point of the object; this will be your home base. You are going to take about 20–40 photos, so it’s OK to take your time. If you are using the mobile app, it will let you know how many photos remain to complete the scan of the object (Figure 6-15).

Figure 6-15. The oscillating indicator level in the Mobile App

You are going to take two laps around your object. Begin by taking pictures low on the object, with the camera facing slightly upward, on the side that has the most detail. For convenience, we’ll refer to this as the “front” of the object (even if it is actually the back or side).

After you complete the first lap, start the second lap from the end point of the first lap. During this lap, try to get more above the object if possible, and tilt the camera slightly downward.

Step 5: Start Shooting

Start by taking a photo at the lower front of the object, which we’ll call home base. (If you are only capturing a 180-degree object, your home base will be to either the far right or left.)

Take a picture and move about 15 degrees. Take your next shot. Repeat. You are doing 3D capture!

The 123D Catch mobile app prompts you by showing where your current view lines up with the blue marking at the bottom left of the screen (Figure 6-16). When you get back to home base (or if you are doing a 180-degree object, get to the far side), start doing your upper lap around the object.

When you get back to home base a second time, you are ready to process your image captures.

Figure 6-16. The white cameras show you the appropriate path around an Object

Step 6: Time to Process

If you are using the mobile app, click the blue checkbox on the upper right to finish capture. Then you can review your shots (Figure 6-17).

After review, click to start processing the capture.

Figure 6-17. Capture of Catch Review on a mobile device

Your capture might take as long as 15 minutes to process (because this all happens in the cloud). I highly recommend being on a WiFi network for this, rather than a cellular phone network.

If you are using a camera and a PC to create your 3D capture, open up Autodesk 123D and upload the photos that you’ve just made in order to process them. This process takes between 10–20 minutes depending on the size of the photos as well as server traffic; you’ll be notified via email when it’s done (Figure 6-18).

Figure 6-18. Screen grab of what a finished Catch looks like on the PC version

Step 7: Reviewing the Results

At this point, you should be able to see your capture in full 3D, either on the mobile device or on the desktop PC app.

If you are noticing a lot of distortion on an area, or a large empty spot on your object, try re-scanning the object. One helpful technique is to put colored dot stickers or small pieces of painter’s tape on trouble areas, so that you’ll remember to capture them more effectively on the second try (Figure 6-19).

Figure 6-19. Example of color marks on shoulders to get better results

Now That I Have a Scan, How Do I Clean It Up?

The easiest way to clean up a scan is to use Meshmixer, another free app that you can find at 123Dapp.com (refer back to Chapter 3 for more information about Meshmixer).

Once you have downloaded and installed Meshmixer on your Windows or Mac computer, sign in to 123Dapp.com, download the model you want to work with from your account, and then import it into Meshmixer to preview, refine, and prepare it for 3D printing (Figure 6-20).

One approach is to use the Analyse → Inspector command in Meshmixer to find the gaps and holes in your object’s mesh: its surface details. Use Meshmixer’s tools to fill in the missing information and make your mesh watertight.

Figure 6-20. Cleaning up a scan in Meshmixer

How Do I 3D Print My Model?

Again, Meshmixer makes this pretty simple: you can customize and order a 3D print of your object from services such as i.materialise, Sculpteo, and Shapeways.

If you prefer, you can also print directly to your own MakerBot, Type A Machine, or other 3D printer.

Figure 6-21. Full color 3D-printed Catch

What’s Next?

Now that you have a primer on 123D Catch, you’re ready to start scanning more objects! For more detailed tutorials and additional information, visit http://www.123dapp.com/howto/catch.