A bit is a unit of measurement for information. 1 bit of information is enough to reduce the uncertainty by 50%. 8 bits comprise 1 byte. Humans count bytes in multiples of thousands, while computers count bytes in multiples of 1,024.
n computers that can encode and decode ASCII, text is stored as a 7-bit sequence. Text consists of letters, numbers, symbols, and control codes.
Unicode is an encoding format which is meant to support every language, ever. Most websites, apps, and interfaces support it today.
Colour is stored as a combination of red, green, and blue. In a computer system, each
An image’s resolution describes its dimensions. Its pixel resolution gives an indication of its physical size (if printed or displayed on a screen), and thus its sharpness. A display with imperceptibly small pixels is often referred to as a Retina display (Apple’s branding) or as a high-PPI display; this requires at least 220 PPI nominally. For an image to be printed sharply, it needs at least 300 DPI.
Humans can distinguish 120 dB of loudness, which means the loudest perceivable sound is a million times louder than the softest perceivable sound. CD audio provides 16 bits of information per sample, sufficient to provide 96 dB. Humans have a hearing range from 20 Hz to 20 kHz. CD audio is sampled at 44.1 kHz. Uncompressed audio thus requires 705,600 bits per second, or 86 KiB/s.
Computers compress image and audio data through a process similar to summarising: it analyses the data using algorithms that use brightness and colour instead of RGB values for images, and different frequencies of sound rather than samples at different points in time for audio. These algorithms then discard parts of the information that human senses do not perceive easily, and reduce the resolution of other parts that human senses are not as sensitive to.
Data cannot be compressed beyond its predictability limit (Shannon entropy) in a lossless fashion. Lossless compression does not discard any information. It generally tries to spot patterns in the data, and represent those patterns with fewer bits, through a combination of predictive coding, run-length encoding, and entropy coding.
A video container can hold one or more audio, video, or text data streams. To encode or decode a data stream, you need to have the necessary codec installed[^1]. Most video runs at 25 or 30 fps, with high-quality video going up to 60 fps. You can use a program like MediaInfo to help you decipher the streams inside a video container file.
A file consists of data, preceded by a file header which describes the data. Software (including operating systems) detect the kind of data contained in a file by 1) glancing at the file extension, 2) looking at its declared MIME type (if any), and 3) checking the file header, in order of difficulty and accuracy.
An HTML file contains markup tags that tell the browser how to interpret and format the text within the tags. Other document formats usually use tags in a similar way. These tags constitute a markup language that any app can use to mark up its own text too.
PDF is the gold standard for universal compatibility (supported by most software and platforms) and visual fidelity (displays exactly the same way). When you need things to appear on a different device in exactly the same way you created it, without having to install additional software, use PDF.
PDF’s markup language is more concerned with how things appear on the page than with what they were originally. Once the PDF is generated, it is almost impossible to retrieve the original data from it. Scanned documents that are converted to PDF may have a text layer generated by OCR that lets detected text be copied from it.