{"id":7046,"title":"Principles of Electronic Image Processing - Scanning","kind":"biblio","url":"https://www.videohistoryproject.org/principles-electronic-image-processing-scanning","version":"d6de0ce675250f24bd7ae4849f7da54a16086bc4752746b24b08d5bc08fd9079","modified":"2026-09-13T21:51:53.8869455+00:00","credits":[{"role":"Author","name":"Sherry Miller Hocking"}],"authorKeys":["Sherry Miller Hocking"],"subjects":["Tool Texts"],"metadata":[{"label":"ETC archive","value":"ETC1043","url":null}],"citations":{"page":"\u0022Principles of Electronic Image Processing -  Scanning.\u0022 Video History Project, Experimental Television Center, 2026. https://www.videohistoryproject.org/principles-electronic-image-processing-scanning.","publication":"Sherry Miller Hocking. Principles of Electronic Image Processing - Scanning. 1978-1980.","risUrl":"https://www.videohistoryproject.org/citation/7046.ris"},"links":[{"label":"Scanned document","url":"https://archive.org/details/ETC1043","relationship":"linked document; contents not retrieved","contentType":"application/pdf"}],"sections":[{"name":"body","source":"VHP record body","generated":false,"characters":19075},{"name":"abstract","source":"recorded publication abstract","generated":false,"characters":84},{"name":"summary","source":"existing VHP generated summary","generated":true,"characters":735},{"name":"archive_summary","source":"existing ETC archive summaries: ETC1043","generated":false,"characters":84}],"content":{"section":"body","source":"VHP record body","generated":false,"text":"\u0022Among the most curious eyes in the whole world of nature is that of a creature the size of a pin\uFF92s head - a little known copepod - copilia. She (the males are dull by comparison) has a pair of image-forming eyes, which function neither like vertebrate nor like compound eyes, but something like a television camera...Exner in 1891, reported that the receptor (and attached lens cylinder) make a \uFF91lively, continuous motion.\uFF92 They oscillate across the mid line of the animal, and evidently scan across the focal plane of the front corneal Iens. It seems that the pattern of dark and light of the image is not given simultaneously by many receptors, as in other eyes, but in a time/series down the optic nerve, as in the single channel of a television camera... The receptors move precisely toward, then away from each other - never independently. The speed of the scan varies from about five per second to about one scan every two seconds.\u0022 RL Gregory Eye and Brain \u0022If the motion we attribute to the film image is as illusion, nevertheless the serial still frames of cinema are discretely apprehensible entities that may be held in the hand and examined at our leisure. When these frames are projected, they are uniformly interleaved with equal intervals of total darkness, which affords us intermittent moments to think about what we have just seen. Conversely, the video field is continuous, incessantly growing and decaying before our eyes. Strictly speaking, there is no instant of time during which the video image may properly \uFF91be said to \uFF91exist\uFF92. Rather, a little like Bishop Berkeley\uFF92s imaginary tree - falling forever in a real forest - each video frame represents a brief summation within the eye of the beholder.\u0022 Hollis Frampton \u0022The Withering Away of the State of the Art\u0022 in Douglas Davis The New Television, 1977 The term scanning describes the process by which the raster is constructed in the cathode ray tube of both camera and monitor. The raster is the visible rectangle of light coming from the cathode ray tube or picture tube of a monitor or camera when no picture information in displayed. In the black and white camera the function of the seaming process is to \uFF91read\uFF92 the object before it as a mosaic of varying light and dark values. These changes are then translated into an electrical signal which can be reproduced immediately on a monitor, further processed by an electronic image processing system or recorded by a videotape recorder for storage and later display. The function of the scanning process in a monitor is to display the image of the object presented to the camera. The camera thus translates the object into a signal which reproduces these fluctuations in light and dark; light energy is thus changed to electrical energy. The function of the monitor is to translate the electrical signal containing the image information into a perceivable image; in the monitor, electricity is converted to light energy. The raster is a rectangular shape constructed by the scanning process in both receiving crt, the camera, and the display crt, the receiver. The proportion of the rectangle\uFF92s length to height is 3:4, a relationship referred to as the aspect ratio of the picture; interestingly, this formal relationship of the Pythagorean 3,4,5 right triangle in an organizing principle evident in the histories of geometry and Western art. The ratio, often expressed as 1:1.33 or 1.33, was also the standard adopted by the Academy of Motion Picture Arts and Sciences for film and is the direct derivation of the video aspect ratio; since the early 1950s a number of other film aspect ratios have been used. In both the camera and monitor, the raster is constructed by a beam of electrons which is focused to a fine point; this point is then moved around in an orderly, repeatable and continuous manner so that the rectangular field of the raster is described. The raster consists of 525 horizontal lines, oriented one on top of the other; the beam draws each line dot by dot. The 525 lines taken together compose one image or frame; it takes the beam 1/30 second to describe one frame, and there are 30 frames or images displayed in one second. The scanning process is linear and sequential; the electron beam excites a single unit of each line, called a picture element or pixel, which emits light. The beam then progresses to the next pixel. In this way the horizontal lines and ultimately the raster are, at a fundamental level, composed of a matrix of dots. A picture element is defined as the unit of the scan line the length of which, or its time duration, equals the width of the line. This dot matrix is the system by which images are organized in the electronic image processing system; it provides a discontinuous surface, composed of discrete, specifiable units which graphically convey force, texture, space and color. This system has correlaries in the art of engraving and in the development of pointillist technique; as a system of image transmission and display it is present in the newspaper reproduction of photographs. Each frame is composed of two separate fields; each field is made up of 262 1/2 lines or exactly half the number of lines comprising one frame. The first field is composed of all the odd numbered lines beginning with line 1 and progressing to lines 3,5,7 and so on to line 525. The second field is composed of all even numbered lines beginning at line 2 and progressing to line 4,6,8 and so on to line 524. Thus the second field fills all of the spaces between the lines scanned during the first field. This method of scanning is referred to as interlace. 2:1 interlace scanning in the camera means that there are exactly 262 1/2 lines in each field and that both fields mesh together precisely to form one frame of 525 lines. The lines of the even field fall exactly half way between those of the odd field. In random or industrial interlace scanning there is no fixed relationship between the lines and fields. The lines of the even field may not fall exactly half way between those of the odd field, resulting in an unstable image. In the first odd field, the electron beam begins at the top left corner of the crt and proceeds toward the right in a horizontal and slightly downward direction until the beam reaches the right-hand side. This process is referred to as a trace. When the beam reaches the right-hand side the beam is shut-off or blanked out during the time it takes for the beam to return to the left side to begin tracing line 3. This motion and the period of time during which the beam is returning from the right to the left are described as the retrace. During this process of return, the crt is blanked out and the beam is shut off; the linear direction of return from right to left is not visible. No picture information is present during this return, although other information critical to the functioning of the system is contained. The beam then returns to trace line 5, moving from left to right and describing another line of the image. After reaching the right side the beam returns to the left during retrace and proceeds to line 7. This procedure continues to the bottom of the crt. The last line to be scanned in this odd-line field is not a whole line but a half line, the beam ending the trace in the center of the line. One complete field of 262 \u00BD lines, or one half of the 525 lines composing one frame or \uFF91complete image\uFF92, is thus described. Figure 1 shows the odd field scanning process. The electron beam is now at the bottom of the tube and must return to the top to begin scanning all of the even lines to construct the second or even field. The return of the beam to the top occurs during the vertical interval. The vertical retrace, or the return of the beam to the top of the crt, is not visible because the screen is blanked out during that time; this process is similar in function to the horizontal blanking interval. The vertical interval also contains no picture information but does contain sync information. The beam is returned to the top of the crt and is located in the center of the first even line, line 2. The beam now constructs all even lines composing the second field in the same manner in which all the odd lines were constructed. The beam traces line 2, moving to the right and slightly down. At the right, the beam begins the horizontal retrace which is blanked out, skips line 3 because it was already scanned in the first field, and begins the trace of line 4. This process for the second field continues to trace all even lines from 2 to 524; line 524 is completely traced. The beam then retraces to the left side of the crt and must return to the top. This return also occurs during the vertical interval and because the beam is blanked out, the return is not seen. This completes the scanning of the second field of 262 even horizontal lines. Figure 2 shows the scanning of a complete frame. Each frame of 525 lines is composed of one odd field and one even field. Each field is composed of 262\u00BD lines. Each line is composed of approximately 460 individual dots. Figure 3 shows the relationships between the structural elements. The frame is often referred to as the smallest complete single image, even though, unlike film, this unit is not displayed as a whole, all at one time. Since each field is constructed of 262 1/2 lines, each field displays only half of the information of one \uFF91complete image\uFF92. The image is composed of two separate displays, each display containing half of the total picture information. This method of display wherein the two fields are alternating rapidly means that although the complete image is displayed once each 1/30 second, the fields are displayed at 1/60 second. This helps to reduce the possibility of the perception of flicker. The eye/brain perceptual systems is generally not aware of the rapidity of change between fields, even though each field is only half of the total picture. We are unaware of the changes and perceive one complete image. Persistence of vision is frequently sited as the phenomenon responsible for this perception. Persistence of vision also functions in the perception of the frame which is actually composed of the dots which make up the lines. We do not see dots or lines because of the rapidity with which the lines are drawn by the electron beam in the crt and also because of the composition of the material which is struck by the beam. In the monitor the material tends to glow for a period of time after the beam has moved on; this also helps to enable us to see an image rather than the dots or lines which compose it. The linear character of the raster is evident on close examination of the monitor screen; the dot character is evident in photographic enlargements of pictures taken off monitors. A single image or frame is two fields, 525 lines or approximately 241,500 dots. This image as recorded exists on tape as two fields, each field consisting of the requisite number of lines. When the tape is played the image is not reproduced as a totality; the image elements are not displayed simultaneously but sequentially. The beam in the monitor excites dots in a linear fashion to form discrete lines; the lines form a field, and the two fields form a frame. Because of the phenomena of persistence of vision and the retentive characteristics of the phosphor surface of the crt, complete images are perceived. The serial nature of image formation is characteristic of video and very unlike film. In video the entire picture exists only as a function of time and is never present as a single entity. The term frame is somewhat misleading because of the implication of a complete image which exists at any one instant of time. The video frame is a process of construction and deconstruction of the image. One field is scanned every 1/60 second; since the frame is constructed of two separate fields, each scanned 60 times per second, one frame is displayed in 1/30 second or 30 frame","offset":0,"nextOffset":12000,"totalCharacters":19075,"complete":false},"rightsUrl":"https://www.videohistoryproject.org/terms-service"}