{"id":6943,"title":"A Building Block Approach to Color Graphics","kind":"biblio","url":"https://www.videohistoryproject.org/building-block-approach-color-graphics-excerpted","version":"a780779483700b715a8133c9758740cb3585343602ad5e151d7a1b21109b7cbe","modified":"2026-09-13T21:51:46.8326626+00:00","credits":[{"role":"Author","name":"Jules Robert Flexer"},{"role":"Author","name":"Gio Wiederhold"}],"authorKeys":["Flexer, Robert J.","Wiederhold, Gio"],"subjects":["Tools"],"metadata":[{"label":"Publication","value":"Computer Graphics Quarterly","url":null},{"label":"Date","value":"August 1979","url":null},{"label":"Volume","value":"13","url":null},{"label":"Issue","value":"2","url":null},{"label":"ETC archive","value":"ETC1154","url":null},{"label":"Other tool designers","value":"Flexer,Robert","url":null},{"label":"Tool","value":"CAT 100/C Frame Buffer","url":null}],"citations":{"page":"\u0022A Building Block Approach to Color Graphics (excerpted).\u0022 Video History Project, Experimental Television Center, 2026. https://www.videohistoryproject.org/building-block-approach-color-graphics-excerpted.","publication":"Jules Robert Flexer; Gio Wiederhold. A Building Block Approach to Color Graphics. Computer Graphics Quarterly. vol. 13, no. 2. August 1979.","risUrl":"https://www.videohistoryproject.org/citation/6943.ris"},"links":[],"sections":[{"name":"body","source":"VHP record body","generated":false,"characters":38774},{"name":"abstract","source":"recorded publication abstract","generated":false,"characters":74},{"name":"summary","source":"existing VHP generated summary","generated":true,"characters":625},{"name":"archive_summary","source":"existing ETC archive summaries: ETC1154","generated":false,"characters":74}],"content":{"section":"body","source":"VHP record body","generated":false,"text":"INTRODUCTION The adage that \u0022a picture is worth a thousand words\u0022 is well accepted by the computing community, although only a fortunate few have had access to devices which provide adequate graphic interaction. Visitors to laboratories where facilities for graphics are available leave with the distinct impression that if such tools would become available to them their productivity and enjoyment of computing would increase significantly. An example of an environment where such activity takes place is XEROX Research in Palo Alto where convincing educational [1] and programming projects [2] are supported using distributed computers which have bitmap display devices using the computer\u0027s main memory. The cost of storing images that way has been one factor in the slow dissemination of graphics capability in commonly available computers. Older systems used bitmaps stored on tracks of drums [3], and these have been used in situations where digitized images are analyzed for robot control [4] and in advanced circuit design [5]. The use of drum tracks for picture storage makes the storage support per display economical if there is justification for at least several dozen displays in close proximity, which will share the storage drum. Less storage is needed if vectors are stored since then only the coordinates of the end points are placed in memory. A vector generator translates the coordinates into a signal which is then drawn on a high quality X-Y CRT screen [6]. This mode of operation was already available in 1958 [7]. Certain graphics applications lend themselves very well to vector displays. We have had good experiences with interactive curvefitting [8,9]. Applications in interactive design [10,11], analysis of three-dimensional objects as molecular structures [12,13], and architectural drawings [12] have been well served by these devices. These applications distinguish themselves by the fact that the original source of the data to be displayed is given as coordinates in space, and the transformation to an image is relatively straightforward. When the source of the data is an image, as obtained by a camera or a scanner, then vector-oriented displays are of little help until the image is reduced to a much simpler abstraction composed of lines or contours. In order to effectively display images a matrix of picture elements has to be displayed, and each picture element (pixel) has to be displayed at a particular brightness. Commercial TV technology provides a standard here, even though pictures as seen on broadcast television rarely reach the desired level of quality. The specifications for TV include the use of 480 horizontal raster lines, which are displayed using two successive fields of 240 interlaced lines each. The signal being displayed is an analog signal, but we can derive from the aspect ratio (width/height, 4/3) of the TV picture frame that 640 pixels per line will be appropriate. The number of levels of brightness or gray scale per pixel is not specified, although 256 levels, as can be produced using eight bits per pixel, make the result indistinguishable from an analog picture image. In practice, most computer-based equipment attempts to reach that level in terms of raster or gray scale resolution. Useful and pleasing graphics can in fact be generated using half of the raster lines (one field) and only 4 bits per pixel to represent 16 levels of gray scale. Similar relationships exist for color display. Whereas true color has high requirements for proper representation, the addition of simple color cues can often greatly enhance the presentation of data. EFFECTIVENESS OF GRAPHICS The power of graphics to communicate can be considered as being due to the ability to create symbols with deep semantic meaning. Pictures of faces, structures, cross-sections, etc. are perceived as having few, but significant, symbols and convey complex concepts. If we trust the rule that human short-term memory is limited to \u0027seven plus or minus two\u0027 symbols, then it becomes clear that a representation using fewer symbols is advantageous [15]. At a high level of abstraction a certain amount of information becomes much easier to manipulate conceptually by the viewer at the display terminal than the same information when it is represented by a greater number of simpler symbols. An obvious example is a function represented by a line versus a list of numbers; a more interesting example is the use of Chernov-faces, where multi-dimensional data is represented by the degree of a smile, the roundness of the face, the angle of the eyebrows, etc.; color might add yet more information. A further dimension of information can be added if the display can be varied over time. Significant computing resources are needed to rotate even a simple picture, but the effect of interaction with a three-dimensional image, due to the high rate of information transfer, is spectacular [16]. Graphics hence represent the potential for an increase of several orders of magnitude of bandwidth in man-machine communication. The question which must now be asked is: Why aren\u0027t we all using graphics? BARRIERS TO USING GRAPHICS We believe that the main cause for the low level of graphics use is due to the high entry cost. Where graphic facilities are justifiable they have been effective, but such justification has rarely existed in educational institutions. Facilities to compute with numbers and characters are available at every level of computer education, but only a few computer science and engineering graduate students have had reasonable access to graphics. The use of a printer to display Snoopy can only discourage the use of graphic methods, especially when the image has to be entered with keypunched cards. Graphic manipulation is hence rarely taught within a regular computer science curriculum, there are few good textbooks [17], and because of the lack of broad interest formalization of graphic tasks has not had the attention that other computer science topics have enjoyed. Since the community which was able to justify graphics is more specialized, no graphic-oriented software has achieved the broad acceptance of FORTRAN or even of FORMAT statements, or the simple elegance of a PASCAL, although certainly many efforts have been made (e.g. [18,19]). Only some manufacturers, notably CALCOMP, have provided support packages which would allow applications to run on more than one machine type. The lack of standards has inhibited sharing of software and hence scientific progress. Nearly every site which wishes to support graphics begins at the most basic level and develops its own conventions. Systems that use interactive displays for menu selection form a sub-area which has seen some high-level efforts. The design of the menu presentation has been aided by frame-oriented programming languages (e.g. ref. [20], but frequently these languages are limited to tables of coordinates, text, and references to procedures or successor frames. A factor which adds to the cost of graphics is the demand on processor time and communication bandwidth when graphics are supported from centralized computers. To drive even a limited number of menu selection terminals at a rate acceptable to physician users requires all resources of powerful computers and high speed (50Kbits/sec) communication lines [21]. It is even more difficult to support real-time graphic input. If the subject to be imaged can move then the image has to be entered into the system at video speeds, which implies that the equivalent of 480*640*8 bits have to be transmitted in 1/30th of a second, that is a rate of 74Mbits/sec. In order to transmit color graphics, two or three times this capability is needed to take care of the three components: luminance, hue, and saturation. Commercial TV broadcast equipment actually uses only an analog bandwidth of 3.5 MHz; to get studio quality, 5-15 MHz are needed. Much less demanding have been input devices such as lightpens, joysticks, trackballs, or tablets, which only enter a point at a time and may move a cursor on the display screen. These devices however collect data at rates which are lower than a typist generates on a keyboard, so that complex images become nearly impossible to construct. Most of the technical problems become surmountable as the technology progresses. The important barrier of entry cost can be attacked now, and we will describe the methods used in our attempt to make a graphic support device which makes a breakthrough in the cost barrier. TECHNOLOGICAL FACTORS The equipment cost to support graphics is composed of the cost of the buffer memory needed to store graphic data, the actual display cost, the cost of internal and external transmission of the signals, and the cost of miscellaneous, but significant, logic and control functions. At high price levels for memory, it was prohibitive to store an entire image as a frame of discrete points and to use the television technique of raster scan to display the image. Recent dramatic price reductions for semiconductor memory make the frame buffer economically possible. For a very high quality picture within the TV image (for instance 454*576*8 bits), 256K bytes of memory are needed; this amount can now be purchased on circuit cards for as low as $4000. At these rates, it is no longer economical to use an X-Y CRT and a vector generator. For many applications less resolution will be adequate. If for instance no gray scale is required then 32K bytes will suffice. A modular approach to the graphic buffer can hence reduce this cost to match the needs. When raster scan techniques are used, the existing TV standards are adequate. A system which is able to accept and generate \u0027standard\u0027video signals can directly interface to any existing piece of TV equipment. All the technological gear developed and mass-produced for the TV industry can become peripheral equipment for such a digital system. The availability of microprocessors makes it reasonable to provide processing capability close to the place where the image is used. Microprocessors bring the possibility to carry out economically the functions needed for image processing, and are available at various performance levels. When the processors are close to data sources the problems due to high external data communication bandwidth are reduced; image-processing functions are controlled through the processor and can be initiated through standard remote-terminal access mechanisms. A number of bus conventions for micro-computer connections have become popular, and a competitive market exists where many types of devices are available from a wide selection of manufacturers. Devices to support graphics should hence be designed to exploit this situation, so that a full range of complementary components becomes available, since the use of graphics spans the entire range of computer applications. There are three immediate consequences if current technology is exploited as we have outlined: The initial cost and the maintenance cost of the available TV input and output equipment are relatively low, even for the amateur. Any properly insulated and modified home TV receiver can have its bandwidth extended to display data at 10Mbits/second by defeating the sound trap in the video amplifier. This is just enough to display 640 pixels or 80 characters per line. Monitors specifically designed for data display can be obtained for as little as $200. If the system is also capable of accepting and converting standard TV signals then inexpensive CCTV cameras can be used as input devices. They are available for a few hundred dollars. If a video processor has both full speed input and output capability then cassette video recorders, starting around $1,000, are available to greatly extend the I/O capabilities of digital video systems. If the equipment is sufficiently modular then digital computer- controlled graphic processing equipment can be used as a building b","offset":0,"nextOffset":12000,"totalCharacters":38774,"complete":false},"rightsUrl":"https://www.videohistoryproject.org/terms-service"}