Otto Schade – A Pioneer with an Insight into Image Quality
Professionals the world over use the Modulation Transfer Function (MTF) developed by Otto H. Schade, Sr., as a definitive metric for predicting and evaluating the performance of imaging components and systems. As SID prepares to award the first Otto Schade Prize for Display Performance and Image Quality, meet the man after whom the prize is named.
by the Editorial Staff
OTTO H. SCHADE, SR., was a giant in the science of predicting and evaluating display-system performance and image quality. He dedicated a major portion of his long and distinguished career to developing a unified general method of image analysis and specification. His dedication to his craft combined with a series of major accomplishments in image science led the Society for Information Display (SID) to name its newest major prize in Schade's honor. The inaugural Otto Schade Prize for Display Performance and Image Quality will be presented at the 2006 SID International Symposium, Seminar, and Exhibition, to be held June 4–9 in San Francisco.
Among Schade's many achievements in image science, the one that secured his place in history was the development of the Modulation Transfer Function (MTF) (see sidebar). This metric can be used to characterize the end-to-end performance of an entire display system as well as the performance of each individual system component from the lens on the camera to the eye of the viewer. Describing Schade's work in the August 1976 issue of Scientific American, William H. Price of Eastman Kodak Co. wrote, "Much of the mystery surrounding lens 'quality' was cleared up in 1951 when Otto Schade, Sr., of the Radio Corporation of America, described his investigation of lenses used in the entire chain of information transmission represented by a television system." Price adds that with Otto Schade's concepts and a computer, "now we can mathematically model the entire photographic system, beginning with the subject and ending with the transfer function of the viewer's eye."
"Not only was he the one who came up with that concept (of MTF), which is used just about everywhere, he also was really the one who applied that concept to the entire system," said Larry Weber, SID President-Elect and Chair of the Society's Honors and Awards Committee. "With MTF you can really figure out how your display should look and what is limiting it. That was a very powerful concept, and so it is highly appropriate that we give that award in his honor."
Weber went on to say that when Lou Silverstein, a member of the Honors and Awards Committee, first suggested a major SID Prize for contributions to display performance and image quality, the entire Committee was immediately enthusiastic about recommending it to the Board of Directors. "Finding a name for the Prize was easy," explained Bernie Lechner, a former President of SID who currently sits on the Honors and Awards Committee, and first suggested Schade as the prize's namesake. "Otto Schade, Sr., was the first to develop a metric that tied perceived image quality to measured display performance."
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Otto H. Schade, Sr. (1903–1981) was an eminent authority on image evaluation in motion-picture and television systems and is best known for developing the concept of the modulation transfer function (MTF).
Otto Schade's contributions to image science go well beyond the MTF. It was in 1938 that he began specialized studies of television circuits, camera tubes, and picture tubes. This work continued over the next 30 years, expand-ing to include optical and photographic elements as well as the human visual system. From 1944 to 1957, he worked to develop a unified general method of image analysis and specification that included not only MTF but also sampling apertures, raster processes, signal-to-noise ratio and granularity, gray-scale transfer curves (gamma), and the human visual system, among other factors. The results of this work were documented and shared with the display community in a series of seminal publications during the 1940s and 1950s. The most representative were "Electro-Optical Characteristics of Television Systems," published in four parts in RCA Review in 1948, and "Image Gradation, Graininess, and Sharpness in Television and Motion Picture Systems," published in the Journal of the SMPTE, also in four parts, from 1951 to 1955.
Over the course of his work, Otto Schade took hundreds of photographs to illustrate the quality of the television and photographic images that he obtained with specific electrical and optical system parameters. A number of these photographs were included in his papers. In 1975, RCA published, Image Quality: A Comparison of Photographic and Television Systems, by Otto Schade, Sr. The book contains 54 of Schade's photographs carefully chosen to illustrate the basic concepts of image quality that he developed and that he describes in the book. In the Foreword, Schade's colleague, Al Rose, wrote, "Otto Schade's career in television and the allied imaging sciences is unique. Many of the concepts that one takes for granted had their origin in his pioneering work in the 1940s and 1950s. At that time, the television, photographic, optical, and visual systems each had its own method for evaluating its imaging properties. And the methods were generally non-commensurable. Schade introduced a set of criteria common to all of these systems, a set that is now universally accepted. His modulation transfer functions and equivalent line numbers can be applied equally to amplifiers, lenses, and the human eye. He recorded the first measurements, in these terms, on the human visual system."
As a part of his investigation into the factors that influenced image quality, Otto Schade constructed a closed-circuit high-resolution television system that served as a testbed for his studies and experiments. He updated and maintained this system through the 1960s, and it served not only as an important tool for the study of image quality and the ongoing development of RCA's broadcast and consumer television products, but also as a valuable resource for those at RCA who were applying television technology to a wide variety of new imaging systems, including space photography, machine vision, surveillance, electronic typesetting equipment, medical imaging, etc.
Otto Schade, Sr., was born in 1903 in Halle, Germany (birthplace of composer Georg Friedrich Händel) and was educated in Germany. He came to the United States in 1926 and worked initially designing radios at the firm of Atwater Kent located in Philadelphia, Pennsylvania. Five years later, he joined the Radio Corporation of America (RCA) Tube Department in Harrison, New Jersey, the start of a lifetime career.
In the course of this career, Otto Schade presented or published more than 30 papers and received 85 patents. His first widely recognized achievement was the subject of his presentation in 1936 before the Institute of Radio Engineers on the electron optics behind the 6L6 beam power tube. Old timers will remember the 6L6 as a mainstay in the output stage of audio amplifiers. It was also popular with amateur-radio operators as an RF output stage. Other landmark accomplishments in electron-tube design resulted in Schade's "Analysis of Rectifier Operation" and "RF Operated High-Voltage Supplies," both published in 1943.
Schade was himself the recipient of many awards during his distinguished career. In 1946, he received RCA's highest citation, the RCA Victor Award of Merit, for his contributions in the field of television. He was a Fellow of the Institute of Electrical and Electronics Engineers (IEEE) and the Society of Motion Picture and Television Engineers (SMPTE) and also received numerous other honors, including the Modern Pioneer Award of the National Association of Manufacturers (1940) and the Morris N. Liebman Memorial Prize of the Institute of Radio Engineers (1950). He was the first recipient of the David Sarnoff Gold Medal Award of the SMPTE (1951). In June 1953, Otto Schade, Sr., was awarded the honorary degree of Doctor of Engineering by Rensselaer Polytechnic Institute. In 1960, he received the Progress Medal Award from the SMPTE for his out-standing contribution in the engineering phases of the motion picture and television industries. In 1968, he received the David Sarnoff Outstanding Achievement Award from RCA for the conception of electronic techniques to determine accurately the response of the total television system, including lenses and photographic films. In 1969, he received the Vladimir K. Zworykin Award for outstanding technical contribution to electronic television from the IEEE. Except for the last two, all of these awards predate the founding of SID in 1962. SID honored Otto Schade, Sr., in 1975 with a Special Recognition Award "for the pioneering application of frequency-response concepts to the analysis and optimization of electro-optic systems." He was elected to the National Academy of Engineering in 1977.
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Otto H. Schade, Sr. (right) of the RCA Tube Department received the David Sarnoff Gold Medal Award for outstanding achievement in television engineering from SMPTE President Peter Mole (left) in 1951.
The Modulation Transfer Function
The Modulation Transfer Function (MTF) is a well-known and widely used metric to characterize the resolution of almost any optical or display component as well as the resolution of overall imaging systems. It is one of the most important benchmarks for imaging performance in the scientific community because it is fundamental.
This metric was first proposed1 by Otto Schade in the 1940s when he took the well-known sine-wave transfer-function methodology that was widely used by electrical engineers to characterize the overall response of electronic systems, e.g., amplifiers, in terms of a frequency-response plot, and applied it to general imaging systems. The resulting MTF, which could be measured and/or calculated, gave the sine-wave spatial-frequency response of the imaging system from the original image at which the camera and lens were pointed to the final image displayed on the screen, a CRT in the case of television at that time and a movie screen in the case of slides and motion pictures.
The concept as it is generally applied to display systems is very straightforward. A sine-wave stimulus of known modulation and spatial frequency is provided as an input to the component or system under test, and the modulation of the resultant output is measured and compared to the input modulation. The MTF is the ratio of modulation of the output to the input. For a given spatial frequency, the MTF lies anywhere between 0 and 100% (often normalized to 0 and 1). An MTF of 0 indicates complete degradation, i.e., the system cannot display that particular frequency at all. An MTF of 1 specifies no attenuation, i.e., the system displays that particular spatial frequency at the original contrast. The spatial frequency is usually specified in cycles/mm (equal to line-pairs/mm) for film-based systems and simply as lines for raster-based systems, e.g., television. To ease comparisons of horizontal and vertical resolution, television engineers have adopted the convention of normalizing the resolution by specifying it in units of TV lines per picture height or TVL/PH.
The beauty of the MTF concept lies in its ability to be applied not only to an entire display system, but to each individual component of the system. Thus, in a TV system, for example, the MTF of the lens, the MTF of the camera sensor device, the MTFs of the various individual electronic processing, transmission, and reception blocks, even including VCRs, and finally the MTF of the display device can be separately measured or calculated and then combined by simply multiplying them together to obtain the overall MTF for the entire system. The MTF is a powerful tool for the analysis and design of display systems and their components. Plotting the MTF provides valuable clues to how a system or component responds to various spatial frequencies. Using conventional signal-processing methods, the MTF approach can be used to mathematically model an entire display system and predict its general response to any arbitrary stimulus.
Recognizing that the final judgment of how sharp an image is involves a subjective evaluation by a viewer, Otto H. Schade, Sr., took the MTF concept further by adding the MTF of the human visual system to the analysis. To quote2 Otto Schade, "It is logical that an external image will be judged to be perfectly sharp when all spatial frequencies within the visual pass band are reproduced with an MTF of unity. It is also logical that all frequencies beyond the visual pass band can be cut off by a filter without effect on the visual impression. Therefore, a cut off within the visual pass band or an attenuation of the MTF in some part of the visual frequency response cannot be assessed properly without knowledge of the MTF of the eye." Schade first obtained the sine-wave response of the eye in 1948 by calculating it from measurements that he made of the eye's contrast sensitivity to square-wave line patterns.1 Subsequently, in 1955, he made direct measurements of the MTF of the eye.3
Otto Schade also observed that the area under the squared value of the MTF curve represents the total sine-wave energy passed by an imaging component or system when stimulated by a flat spectrum, i.e., a random grain structure or white noise. This area can be represented by an equivalent MTF, which Schade denoted MTFe, of rectangular shape having a constant response up to a spatial frequency fe or line number Ne, where the value of MTFe drops abruptly to zero. Schade proposed that this "noise-equivalent line number," Ne, be used as a single number to rate the sharpness of an imaging process, component, or system. He demonstrated this measure of sharpness with a series of photographs taken in 1952 and with a series of tests4 he conducted that same year under a Navy contract to establish the parameters of a theater TV system.
1Otto H. Schade, Sr., "Electro-Optical Characteristics of Television Systems," published in four parts in, RCA Review 9 (1948).
2Otto H. Schade, Sr., Image Quality: A Comparison of Photo-graphic and Television Systems (RCA Laboratories, Princeton, New Jersey, 1975).
3Otto H. Schade, Sr., "Optical and Photoelectric Analog of the Eye," J. Opt. Soc. Am. 46, 721-739 (September 1956).
4Otto H. Schade, Sr., "Wide-Angle High-Definition-Television Systems," Contract N60NR-23606, Final Report by RCA Laboratories for the Office of Naval Research, Special Devices Center, Port Washington, NY, pp. 1-88 (August 1952).
– Bernard J. Lechner
The evidence of these many awards is scattered around his son's, Otto Schade, Jr., home in Caldwell, New Jersey. The Sarnoff medal from 1968 and the Zworykin medal from 1969 sit somewhere amid plaques for other awards going back as far as 1940.
In a recent interview, the details of his father's life and career do not escape Otto Schade, Jr., a 74-year-old retired electrical engineer, who still lives in the Caldwell house that he built with his father in 1956. But his soft-spoken, cheerful, and incredibly vivid recollections may be as much a function of necessity as of pride. Otto, Jr., who sometimes refers to himself as the "Purveyor of the Legend," still gets telephone calls from strangers asking if he has a copy of one of his dad's early papers. Even 24 years after the death of Otto Schade, Sr., Otto, Jr., fields inquiries about his father's life story.
When the 22-year-old Otto Schade left Germany in 1926, he followed Marta Wenzel, a former governess in his father's home, to America with her mother and younger brother, Fred. Otto and Marta married in a civil ceremony in Philadelphia and, after traveling back to Germany for a second, church wedding, the couple aptly settled in a section of Philadelphia called Germantown, and Otto Schade started work at Atwater Kent.
In 1931, still struggling after the stock-market crash of 1929, Atwater Kent shut its doors on a Friday afternoon, according to the story Otto always told his son. But, true to form, Schade wasted no time getting in touch with some contacts at the Radio Corporation of America (RCA) in Harrison, New Jersey. He reported for his new job with RCA on Monday morning.
"There was very much a European tradition of looking after yourself because there was no one else to do it," Otto, Jr., explains. "My dad was so fortunate in that he always had a job that was well-paying, and my mother could stay at home until the war years (when she worked in the tube division at Westinghouse). Even during the Depression, the family lived a very normal life. There was no problem eating, or keeping the house."
But life with Otto Schade brought about some unique perspectives for his son. Sometimes Otto, Jr., had to cancel dates to serve as the test audience for his father's lectures, and the planned building of a model-train layout with his son in the cellar was scrapped in favor of a home darkroom to further study image quality.
Few sons in history have heard the following command from their father: "Sit down, I want to get the sine-wave response of your eye." "It had something to do with looking at images and then test patterns and seeing what you could see," Otto, Jr., recalls. "He would change the intensity or the brightness of the image or the frequency of the pattern itself and say, 'What can you see on this test pattern and how far down can you see it before the individual black and white lines start to blur?' "
Otto, Jr., remembers a time when RCA was tugging at his father from all directions to move his operation, from the Tube Division in Harrison to the Sarnoff Laboratories in Princeton – Schade refused. He had recently completed construction of a new family home in Harrison and was not about to leave it, Otto, Jr., remembers.
He said, "I just built this new house and I want this new house. They said 'We will build it for you over again in Princeton.' At least that is the story he would tell. But he said 'No, I would like to stay in Harrison,' " Otto, Jr., says. And stay he did. Otto Schade still lived in that same house when he retired from RCA in Harrison in 1968 as Staff Engineer, a position that RCA first created for him. He continued as a consultant to RCA until 1974.
Even in retirement, Schade was constantly working, according to Harold Albrecht, who was Schade's go-to technician for about 25 years toward the end of his RCA career and well into his retirement years. When he tried turning his focus to gardening and playing the piano, engineering was still a huge and inextricable part of his daily life. In one anecdote, Albrecht recalled how he and Schade had made a very-high-resolution TV camera with a beam aperture with a diameter of 1/1000 in. with simple shop tools. Such was the work ethic of Otto Schade – a tireless combination of scientific vision and hands-on application.
At the time of Otto Schade's death in 1981 following his 78th birthday, William Webster, the Vice President of the RCA Laboratories David Sarnoff Research Center wrote, "Those who had the good fortune to work with Otto Schade, Sr., or even to know him in a passing fashion, would characterize him as a gentle, unassuming, thoughtful man who combined the Old World ideals of perfection with understanding of the real world's deficiencies. He was a superb teacher of the younger engineers who worked with him and, often, of the older managers he worked for." •
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This high-resolution test pattern, developed by Otto Schade in late 1961, was used to demonstrate that video imaginery using a 4.5-in. return-beam vidicon with a bandwidth of up to 100 MHz could achieve a resolution comparable to that of photographic film.