Information theory: sending a digital image through the Internet

In this week’s readings we explored fundamental concepts around information and data. The nuances of the terminology used in different fields and how the meaning changes in between them: meaning, value, symbol, information, among others. Let’s attempt to de-Blackbox the process of sending a picture from one computer to another computer through the internet.

When making the argument of information theory, Shannon makes a distinction:

“The fundamental problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point. Frequently the messages have meaning; that is, they refer to or are correlated according to some system with certain physical or conceptual entities.” (Shannon, 1949)

Applying this to the case of sending a picture, Shannon differentiates between the picture as we see it and understand it as a concept and the information being sent and received. He is saying that communication’s only concern is how to move the bits from one computer to the other one. In this particular case those bits represent an image, but it can be other types of data. To that sense he says:

“These semantic aspects of communication are irrelevant to the engineering problem. The significant aspect is that the actual message is one selected from a set of possible messages. The system must be designed to operate for each possible selection, not just the one which will actually be chosen since this is unknown at the time of design.” (Shannon, 1949)

Therefore, the meaning of those bits does not change or impact the action of selecting sending a package of information and receiving it on the other side. The way I envision it is as a series of translations of different types of D-information in order to be exchanged and reproduced through E-information. In that sense, E-information is the bits, D-information is the type of data that those bits represent.

  1. The picture is encoded into a certain type of structured data that is stored and processed by the computer: 

    “Computational devices (large or small) are designed to store and process bits (binary units) — millions of on/off switches — which are encoded, at a different design level in the system, as units of the data type that they represent.” (Irvine, Intro, pp.3)

    Let’s say the size of our picture is 24mb. Those 24mb need to be received at the destination in order to be decoded again into the actual picture. In order to do that:

  2. The file (picture) is divided into packages of encoded bits that will be sent through the network. The router, as the name suggests, send the packages through different routes. Every package has encoded information that states its origin, its destination, its number in the total of packages of the file, and the actual encoded information that is a partial size of the file. 

    “Programming “code,” when translated into these mathematical-electronic mappings, is designed to “encode” our symbolic “data” structures together with the logical and mathematical principles required for transforming them into new structures” (Irvine, Intro, pp.3)

    Let’s say our picture of 24mb is divided into 4 packages of 6mb each:

  3. The packages arrive to their final destination, after bouncing around through other serves in the network. They arrive not necessarily in a numerical order. The destination router receives the packages as they arrive.
  4. The computer arranges the packages in the right order until it has the file in its total.
  5. Our computer’s software decodes the file of 24mb into the visual representation of our picture.

To address one part of the prompt question for this week: How do we recognize the difference between E-information transmitted and received (successfully or unsuccessfully) and what a text message, an email message, social media post, or digital image means? 

E-information transmitted and received are the packages of bits sent through the network. Meanwhile, our picture or digital image is D-information, data type in which these bits are structured to have the specific meaning of a digital image. Therefore, there is a process of encode-decode from the sender to the receiver. However, at the core of what Shannon proposed is the idea that the process of measuring and encoding information is independent from the meaning of said information.

 

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