science

X-Face

X-Face is a science 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 X-Face rather than just read about it. In short: An X-Face is a small bitmap (48 × 48 pixels, black and white) image which is added to a Usenet posting or e-mail message, typically showing a picture of the author's face. The image data is included in the posting as encoded text, and attached with an 'X-Face' header.

Key takeaways

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

Reference excerpt

An X-Face is a small bitmap (48 × 48 pixels, black and white) image which is added to a Usenet posting or e-mail message, typically showing a picture of the author's face. The image data is included in the posting as encoded text, and attached with an 'X-Face' header. It was devised by James Ashton. It is one of the outgrowths of the Vismon program developed at Bell Labs in the 1980s. While many programs support X-Face, most of them are free software and based on Unix or its variations, such as KMail or Sylpheed. The most common email programs though, as used in business and most domestic environments, do not handle X-Face natively, and the information is silently ignored. Even where Unix is widely used (university and research environments), it has never been adopted to maximum potential (for example, by searching for senders by X-Face). A further development is the Face header developed in 2005, which also allows for color images in PNG format, and can be used by the Thunderbird addon Display Contact Photo, as well as some other mail readers. Another approach to include the sender's picture in an e-mail was used by Apple: Mail displayed the picture if the mail included the X-Image-URL header. In 1992, this feature was originally implemented in NeXTmail, Mail.app's ancestor. X-Image-URL accepts http or (anonymous) ftp to download the picture; typical size 64x64 pixels. As of Mail v4.5, the feature is no longer supported.

See also iChat has a similar though not compatible feature called picture icons XBM is a general monochrome image format supported by xbm2xface.pl FFmpeg and Netpbm tools can create X-Face images Vismon Brand Indicators for Message Identification, a similar feature for brands, based on cryptographic authentication

References

External links "compface". Freecode. - utilities and a library for converting to and from the X-Face format Steve Kinzler (2005). "Faces Archive". Retrieved 2014-01-06. applications that can use picons and/or X-Face mail header entries

Illustrations

X-Face: X-Face example. — X-Face example.

Worked examples

Example 1 — a first encounter with X-Face

Start with the simplest possible case. Write down what X-Face claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 X-Face 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 X-Face 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 X-Face

In research: X-Face appears in science 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 X-Face 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: X-Face is common in secondary-school and first-year university syllabi. It links to neighbouring topics Email, Usenet, so understanding it makes those chapters shorter.
In everyday life: Look for X-Face 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 X-Face in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what X-Face 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 X-Face out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is X-Face in simple terms?

Why does X-Face matter?

Because it connects several science 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 X-Face?

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 X-Face.