physics

Motiongram

Motiongram is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Motiongram rather than just read about it. In short: A motiongram is a spatiotemporal display of motion, created from a video recording. Motiongrams are created using a video processing technique, in which a motion image is collapsed into a series of 1 pixel wide stripes and plotted next to one another.

Key takeaways

Motiongram belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Motiongram to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Motiongram from memory before moving on to harder problems.

Reference excerpt

A motiongram is a spatiotemporal display of motion, created from a video recording. Motiongrams are created using a video processing technique, in which a motion image is collapsed into a series of 1 pixel wide stripes and plotted next to one another.

Challenge The traditional way of representing (human) motion visually, is either by displaying individual frames from a video file as a keyframe display or by doing one or more forms of feature extraction and subsequent plotting of the resultant data. Neither of these are ideal to give a good impression of the actual motion happening in the sequence. Keyframe displays only show postures and not motion, while feature graphs often rely on multiple analysis steps. Motiongrams are useful as an intermediary step to show spatiotemporal information of a movement sequence, but with no need for doing a full analysis of the data.

History The term motiongram was first proposed by Alexander Refsum Jensenius in 2006, and the technique has later been refined by him and others. The technique was inspired by the pioneering work of Muybridge and Marey from the 19th century, as well as the slit-scan community in the 20th century. Motiongrams resemble slit-scan photographs, but are different in that they are created from frame-differenced motion-images. The result is that only motion is shown in the final display.

Implementation An overview of creating a motiongram is shown in Figure 1. The process starts by reading a video stream, and doing simple image adjustments, e.g., changing the brightness and contrast. The next step involves producing the motion image by calculating the absolute frame difference between successive video frames, followed by applying some noise removal algorithms. The motiongram is created by calculating the normalized mean value for each row or column in the motion image. This means that for each image matrix of size MxN, a Mx1 or 1xN matrix is calculated. Drawing these 1 pixel wide “stripes” next to each other over time results in the final motiongram. The motiongram technique has been implemented as modules in the open framework Jamoma for Max, as well as for the EyesWeb platform and in Matlab. There are also two standalone applications for OSX and Windows: VideoAnalysis (non-realtime) and AudioVideoAnalysis (realtime).

Examples Motiongrams allow for quick navigation in video material and for comparative analysis of motion qualities. Although quite rough, it is easy to see differences in the quantity of motion and similarities in upward/downward patterns between motion sequences.

Limitations Since motiongrams are made by averaging over either the rows or columns of a video file, only one dimension will be shown in the final motiongram. Thus a horizontal motiongram will mainly represent vertical motion, while a vertical motiongram will mainly represent horizontal motion.

References

Illustrations

Worked examples

Example 1 — a first encounter with Motiongram

Start with the simplest possible case. Write down what Motiongram claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Motiongram before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Motiongram ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Motiongram

In research: Motiongram appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Motiongram in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Motiongram is common in secondary-school and first-year university syllabi. It links to neighbouring topics Motion (physics), so understanding it makes those chapters shorter.
In everyday life: Look for Motiongram outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Motiongram in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Motiongram means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Motiongram out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Motiongram in simple terms?

Why does Motiongram matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Motiongram?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Motiongram.