{"id":7047,"title":"Principles of Electronic Image Processing - Signals","kind":"biblio","url":"https://www.videohistoryproject.org/principles-electronic-image-processing-signals","version":"d266f5531d77c283496c534b6ce5254f4a1d4fa0e13c9c2d69ac835123d7e7ab","modified":"2026-09-13T21:51:53.8869868+00:00","credits":[{"role":"Author","name":"Sherry Miller Hocking"}],"authorKeys":["Sherry Miller Hocking"],"subjects":["Tool Texts"],"metadata":[{"label":"ETC archive","value":"ETC1044","url":null}],"citations":{"page":"\u0022Principles of Electronic Image Processing - Signals.\u0022 Video History Project, Experimental Television Center, 2026. https://www.videohistoryproject.org/principles-electronic-image-processing-signals.","publication":"Sherry Miller Hocking. Principles of Electronic Image Processing - Signals. 1978-1980.","risUrl":"https://www.videohistoryproject.org/citation/7047.ris"},"links":[{"label":"Scanned document","url":"https://archive.org/details/ETC1044","relationship":"linked document; contents not retrieved","contentType":"application/pdf"}],"sections":[{"name":"body","source":"VHP record body","generated":false,"characters":21037},{"name":"abstract","source":"recorded publication abstract","generated":false,"characters":84},{"name":"summary","source":"existing VHP generated summary","generated":true,"characters":739},{"name":"archive_summary","source":"existing ETC archive summaries: ETC1044","generated":false,"characters":84}],"content":{"section":"body","source":"VHP record body","generated":false,"text":"\u0022The universe as we knew it until now was constructed on information of light, which reached our eyes and provided a model of the conscious universe. But now, with radio astronomy, we are getting a very different notion of our universe. First of all, we receive information which is not visible. It\u0027s not points or spheres anymore. It\u0027s energy which is not a permanent state; it is permuting, as a matter of fact, all the time. So that suddenly, through the instruments we have, we are reconstructing the universe in some visual sense, because eventually we translate radio waves into some visual model. We are now trying to visualize space which exists only as electromagnetic forces...It\u0027s the notion of the organization of energy in time that for me is the key to all sorts of changes within life.\u0022 Woody Vasulka, in Johanna Gill, Video: State of the Art 1976 As a kinetic as well as an electronic form, video concerns itself with the time/space equation. Video image movement occurs within a predetermined space, and the process of change, by definition, is a temporal event occupying a specific length of time. Changes in the time frame or time base of the signals which define the image result in changes in the duration of images and in the locations of sections of images within the two dimensional space of the image\u0027s display. On the level of electronics, the very construction of the video image, its generation as well as its display, is time dependent. The composition of the signal, then, defines the visual nature of the image as it exists in time; it dictates both the appearance of the single \u0022still\u0022 image, which exists within a specific length of time, and its behavior through time. On a primary level, the signal can be viewed as the art-making material; the creation of an electronic image is an architectural process and constructed in time. The signal refers to changes in energy levels and reveals a physical nature by forming and influencing images. Specific devices in an electronic image processing system perform specific functions or operations on signals, generating and altering the signals, or codes, and therefore the resulting images. In this way the hardware of the system can be viewed, in part, as a \u0022carrier of aesthetic definitions.\u0022 There are several general categories of signals specified by the processing system which include video, audio, control, and synchronizing or timing signals: as shall be seen, signals may perform functions within several categories. One signal, for example, can influence an image and also produce a sound. The term \u0022signal,\u0022 derived from the Latin signum meaning sign, refers in a general sense to the use of conventional symbols which refer to a verbal description of a concept or event. A signal then is a translation of the description of an event from one set of symbols to another set of codes. It is the representation of the event. The signal conveys information concerning the state of the event in any given instant through time. Video images are codes of information conveyed by signals. The specific video picture information conveyed by a signal is in the form of changes in voltage; changes in voltage dictate changes in the information being carried. Voltage changes can be categorized in terms of changes of strength, increased or decreased voltage, and changes of direction, alternating or direct current signals. Electricity is usually defined as the orderly movement of electrons through a conductive material. When a voltage is applied to a conductor, a force field is established which causes electron movement and therefore electrical energy. The rate at which electrons move past a given point is a measure of current strength expressed in amperes or amps. When a current of one amp flows through a conductor, 6 x 10 raised to the 18th power electrons are passing a given point each second. Electrons move only when an unbalanced electrical force or potential difference is present; voltage is a measure of the force causing electronic motion and is often described as electrical force or pressure. Ground is a reference point which has zero potential energy or zero volts. Because of the properties and dimensions of the conductive material, there is a resistance to the flow of electrons. Resistance is often likened to friction and is measured in ohms. It refers to the impedance of a current flow and results in the dissipation of power in the form of heat. Although the degree of resistance is dependent on the nature of the material, the resistance of any given material is constant. Ohm\u0027s Law expresses the relationship between current, resistance, and voltage; it states that voltage equals current, measured in amps (I), multiplied by resistance, measured in ohms (R). Because the resistance of material does not change, voltage is proportional to current. Increases or decreases in voltage simultaneously produce proportional increases or decreases in current. A watt is a unit of electrical power produced when one volt causes a current of one amp to flow through a circuit. Two of the effects of electrical current are heat and magnetism. The resistance of the conductive material to the flow of electrons produces heat; this is easily demonstrated by the warmth of an incandescent electric light bulb. An electrical current also induces a magnetic field; this can be seen in the deflection of a compass needle placed near a wire through which a direct and steady current is flowing. The force of the magnetic field is at right angles to the direction of current flow. Michael Faraday in 1822 demonstrated the reverse of this law by showing that an electrical current can be induced by a magnetic field. A flow of electrons can thus produce a magnetic field and is also produced by a magnetic field; a magnetic field can therefore be employed as a means of controlling the movement of a flow of electrons, a process basic to the functioning of the scan motions in a video camera or monitor and also the foundation of many scan processing devices. Electrical signals have a waveform which conveys the time limits of the event, the strength of the event and the direction of change of the event relative to a base line or reference point. The electrical signal can be graphically displayed in a number of ways. On a fundamental level the waveform of an electrical signal is displayed as an XY plot of voltage changing through time. By convention, the horizontal or X axis represents the time dimension and the vertical or Y axis represents the voltage or signal strength. An oscilloscope is a test instrument which visually displays any electrical signal as a change in voltage through time. A waveform monitor is a specialized oscilloscope which graphically portrays the composite video signal. In discussing a black and white video signal, the range of the video or picture portion of the entire signal provides an indication of the relative brightness or darkness of the image represented by the signal. A higher voltage level measured on the Y axis indicates a whiter portion of the image while a lower level indicates a blacker portion of the image. The concept of graphic representation of waveforms is crucial to the understanding of an image processing system. As we will see, the time dimension or time frame of the signal may be extremely brief as in the representation of a single line of the video image which occurs in 1/15,750th of a second; the time frame may also be relatively long as in the representation of a frame of video, a collection of 525 lines which occurs in 1/30th of a second. The basic XY format can also be extended to incorporate a third parameter represented along the Z axis which can be conceived of as a vector extending out into space. This notion is important to understanding the technique of colorization. Woody Vasulka developed a technique using this type of vector diagram to locate parameters of the time frame of a video image, employing the Rutt/Etra Scan Processor. This graphic representation defines the line rate, field rate and intensity information. A waveform can be described in terms of its shape, the number of times it repeats per time unit, its strength, placement and direction. A waveform may begin at any point but when it returns to the point past which it started, the waveform has completed one cycle. Cycle refers to the completion of one rise, fall and return of the signal. It is important to note that the waveform may pass through a number of times the particular voltage at which it began before one cycle is completed. For example, the sine wave begins at the point exactly half way through one cycle before ending at this value at the second cycle after beginning. The time it takes for one waveform to be completed is called the period of the waveform. The term periodic refers to a waveform wherein a regular, repeating pattern is observable as the voltage changes through time; sine, square, and triangle are all periodic waveforms with specific shapes. Sine, square, and triangle are the basic waveshapes which can be combined with each other to produce complex waveforms. As we will see, the sine wave is actually the fundamental form from which square and triangle are derived. Noise refers to a signal which is not periodic but random in nature, with unpredictably varying signal strengths; it is often defined as extraneous information present in the signal which is determined to be undesirable either through the process of comparing the signal to a reference signal or by personal decision. Noise can be manifested either aurally or visually and can also be used as a control. Snow is an example of video noise; snow is a random organization of monochromatic blotches and is part of the vocabulary of image processing because it is used as an image element in composition in much the same way that audio noise is used in electronic music composition. The number of times a waveform is repeated per unit of time is called the frequency of the waveform; frequency then implies the speed of the signal. The number of cycles the signal completes in one second is measured in cycles per second expressed in Hertz or Hz. The amplitude of the signal refers to the maximum strength attained by the signal. It is measured by the height of the waveform expressed to volts. The signal may have both a positive and negative voltage dimension. The reference line of zero volts is called ground. The total voltage excursion of the signal, obtained by the addition of the maximum positive and maximum negative points reached by the signal, is referred to as peak to peak voltage and is abbreviated Ppv. The term gain defines the total peak to peak voltage excursion of a given signal and indicates the relative strength of the signal. An increase in the gain of the signal causes an increase in the signal level and conversely, a decrease in the gain results in a decrease in the signal level; gain thus equates with the amount of amplification of the signal. It expresses the ratio of the amplitude of the input signal to the amplitude of the output signal. The term attenuate means to reduce in force or intensity; with respect to an electrical signal; attenuation refers to the lowering of the amplitude of the signal with respect to ground. Instantaneous amplitude refers to the distance between a specific point in the waveform and the base line or ground and is expressed in volts. The signal can be further defined by its positive and negative voltage dimension. An AC or alternating current refers to a signal which has both a positive and negative voltage dimension. An AC voltage rises to a maximum point and then falls through zero to a negative voltage level which is equal in amplitude to the maximum. A DC or direct current voltage does not change direction; the signal does not vary and is always either positive or negative. Polarity refers to the existence of two opposite changes, one positive and the other","offset":0,"nextOffset":12000,"totalCharacters":21037,"complete":false},"rightsUrl":"https://www.videohistoryproject.org/terms-service"}