In this post I hope to provide you with a very broad overview of the motion capture processes from beginning to end. I’ve tired to cover many of thing you will need to think about at each stage of the process in the order I usually approach a new project.
Hopefully this will help you understand the work involved with motion capture and avoid many of the mistakes and frustration people often encounter.
Enough waffle, quickly to the capture cave!
Table of Contents
- Post processing
Build the skeletons
- You will need to decide how many skeletons you want the motion capture data applied to and who will do the applying.
- Re-mapping the motion capture to different sized skeletons will create artifacts which will need editing.
- The usual best practices for building a skeleton apply to building a skeleton for mocap purposes
- Local rotations aligned down the joint
- Continuous skeletal hierarchy
- Degrees of freedom set correctly
- Rotation order set to minimise gimbal lock
- Consistent joint naming convention
- Name spacing
- Freeze transformation and scale
- Remove history nodes from mesh
- Scale node to transfer between your scene scale and mocap (real world)
Gather reference material
- Write character descriptions so everyone has a clear understanding of what each character is like.
- Using character and environment renders can really help explain your ideas quickly and easily.
- Referencing video files from films or your own rehearsals will help demonstrate the type of actions you are looking for.
- If you have permission show any existing footage or game play videos to provide an overall feeling for your project
Consider move requirements
- What is the motivation for each move you want to capture?
- How do the preceding and following events affect the action about to happen?
- Does the performer need to hit specific marks to hit during the take?
- What is the general attitude of the character and how does this affect their movements?
- Is each move variation clearly distinguishable from the other?
- How does the location of the move in the scene affect the performers move on the mocap stage?
- What should the proximity of the performer be to an object or the scenery when performing an action?
- What start and end poses does each action require?
- Are there any speed, time or distance requirements for the action?
- Does the action need to be synchronised with an audio file?
Write a Move List
- Your naming convention should be easy to understand and describe everything you need to know about the move.
- Assigning a shot number to each move will make it easier to find and describe than the more complicated move name.
- Estimate the duration of each move as this will also help you calculate the cost of your motion capture data.
- Prioritise the moves to cover all the essential on the shoot and the moves are returned in in the best order.
- Make a note of the required number of actors for each take.
- A short description of the move will help remind you what the naming convention actually means.
- It may be possible to source your props directly from the motion capture company or through a recommended company.
- Using replica “mocap friendly props” with identical weight and proportions to the actual props may be cheaper, safer and necessary for safety and data quality.
- You will need to know the dimensions of all the props you intend to use on the shoot.
- Check the scale of the props against your character before you get the built.
- If the characters costume affects the way they move you should try to replicate this on your performer.
- It is possible to attach markers to a costume to capture reference data, but you will need to find a way to transfer that data on to your scene object.
- Make sure the mocap company is aware of any costume changes your character make as this can affect marker placement and the solving process. .
- Make sure the scenery you require is “motion capture friendly” so that it doesn’t affect the motion capture equipment.
- Check the floor in the motion capture studio matches the terrain in you scene.
- You will need to know the dimensions of all the parts of the scenery the performer interacts with.
- Check the scenery and the performer will fit in the volume.
- You can use tape on the floor to mark out the scenery so everyone can visualise the space without having to pay for construction.
- If you are scaling the performer to match your character don’t forget to scale the environment as well.
- Check the scale of your environment to your character, especially if you are scaling the character.
- Motion capture systems are limited by the range of their sensors so you may need to consider how this will affect what you want to capture.
- Consider the amount of height and floor space you will need for each move, as this may require the mocap sensors to be configured differently.
- It may be necessary to split your actions in logical sections that will be easy to recombine if they won’t fit within the rage of the sensors.
- Capturing the performers face and body simultaneously may limit the amount of space available.
- Allow time to plan your shoot thoroughly as this can save you time and pain when you come to the post work.
- If you decided to arrange a second shoot, allow yourself enough time to check all the data from the first shoot and plan any new moves that need capturing.
- The same actors can play multiple characters, but it will require careful planning and rehearsals.
- It is possible to have different performers playing the same characters if you can’t find someone who is a good actor and has the specialist skills you require.
- Ask the motion capture company for recommendations for your performers or talent agencies if you don’t know where to start looking.
- Arrange an audition day for the performers to make sure they can provide the performance you are looking for.
- Try to match the performer proportions to your character’s as this will give a more accurate solve when re-targeting the data to your skeleton.
Shoot Running Order
- You should plan to capture about 100 moves per day, although this will vary depending on the complexity of your moves and the amount of set up they required.
- It is a good idea to priorities your moves in case you find yourself running out of time on the shoot.
- Arrange your moves so you don’t tire the performer out early on in the shoot and leave them unable to perform the rest of the moves easily.
- Group moves with the same base poses so it it easy to for you and the performer to remember what they are like.
- Group moves that use the same volumes and arrange in advance when the best time will be to change the volume.
- Group moves that require the same props and scenery set ups together as this will save time and pulled muscles moving equipment.
- It is worth considering what type of data you will get the data back from the motion capture company as this will affect the amount of post work it will require..
- Clean marker data is simply the data from the sensors which will require mapping to your character.
- Mapping to an actor skeleton for an accurate solving but may still require mapping to your characters skeleton.
- Mapping to your character skeleton may require editing to remove re-targeting artifacts such as mesh intersections.
- Edited Data would mean all the editing was complete or even integrated in to your scene.
The motion capture company
- Try to cover as many of the above points before you contact a motion capture company so you have a clear idea what you want to capture.
- Arrange a test shoot to check the facilities, equipment and quality of data the company can provide.
- Try to capture test moves that represents the types of moves you intend to capture.
- Review your move list with the mocap company so they understand what you want to capture and can raise any problems or suggestions to help.
- Check what they estimate the turn around time for your data will be.
- Ask if they have experience with similar projects and what advice they could offer.
A typical shoot
- On arrival at the studio, briefly run through what you plan to capture and go over any any questions or changes you may have.
- The motion capture system will require calibrating before you can start shooting to allow the sensors to record the data accurately.
- Each performer will be taken through a Range Of Motion which is used to further help the calibration and the processing of the data after the shoot.
- Take reference photos of the performers, props and scenery to refer to later especially if you plan to do more than a 1 day shoot.
- Set up a camera to record the performances for reference when making your selects and editing the data after the shoot.
- Try to differentiate the performers with different coloured bands or suits to help clearly identify them in the video files.
- Brief the performers about your project and the characters they will be playing but leave out the specifics of each move until you are ready to capture it.
- Before recording, rehearse each new take to make sure the performers and the motion capture company are happy with the action.
- Performers may need to start in a specific pose and then move to your required start position to help the motion capture system.
- When everyone is happy and the mocap system is recording shout “Action!“
- If the action wasn’t to your liking give the performers feedback and try another take.
- It can be useful to capture everything you think of during the shoot if you are only paying for the data you have processed.
- Always check the recording was successful and contains all the information you need.
- Keep a log of everything you capture, including –
- How many takes you record for each move.
- How many actors were involved
- Any problems with the move
- Who had what props
- Favourite takes you may want processing
- Which performer played which character
- Any notes required for processing
- Some motion capture companies can offer live pre-visualisation and virtual cameras which allows you to view the performers motions re-targeted to the characters in real-time.
- When you’ve called “wrap!” it’s a good idea to confirm how you want your data to be delivered and who will be the contact person from each company.
Directing a Shoot
- Choose one person to direct so any instructions and questions can filtered through one person to save confusion.
- It may be possible to remain in the volume while capturing, but be considerate to the requirements of the performers and the motion capture company.
- Don’t just give the performers an action, explain the motivation, context and attitude for each move as this will help their performance.
- Remember to explain any special requirements for each move to the performer.
- Mark guide lines on the floor to help performers hit specific marks.
- Check the performer is in the correct start and end poses for each move.
- Optical motion capture data will require tracking to resolve issues like missing or incorrectly identified markers which may require specialist software.
- Inertial motion capture data will need editing to resolve floor contacts issues which can often be achieved in the software supplied with the system.
- The data may require re-sampling as it is captured at a much higher frame rate than you will use in your final scene.
- The clean data will require mapping to objects with either a simple constraint set up or with more complex global optimisation software.
- Select a couple of files to test your pipeline before beginning the bulk of your processing.
- A good folder structure is essential as you may have raw, clean, edited, final and exported version of every file you capture.
- Set up a system to track what stage each file is at
- Mesh intersections will occur if there are any differences between the character and the performer portraying them.
- Any interactions between the character and themselves or other objects will probably require some kind of editing.
- If the file needs to loop continually you will need to edit it so the first and last frames are identical.
- If the file needs to blend with other clips the same base pose will need to be added to the start and end of each file which may create artifacts that will require further editing.
- Try to edit the files by applying offsets to exaggerate key poses that already exist.
- The more you have to change the motion capture, the more of the subtleties you will loose and the more difficult the editing will become.
- Sometimes it can be quicker to re-capture an action rather than try to edit it..
- Single actions captured in multiple takes will require blending in to a single take before they can be used.
- Multiple characters and props from different takes may require combining in to one scene.
- Generic character action may require re-aligning with existing elements within a scene.
- Character action my need combining with object animation if the character is traveling in a car for instance.
- Performances may require editing and re-timing for them to synchronise with audio tracks.