Continued from Orthochromatic Photography, Part 2…
Color Photometry and Sensitometry
Sensitometry, as we discussed earlier, is the process of calibrating printing plates. The process of calibrating any device requires known constants. We calibrate scales using objects with known weights. We calibrate rulers using objects with known lengths. Measurement devices, in general, are calibrated using an object with known dimensions. Photographic plates measure light. Differing amounts of silver deposits present on a developed plate represent (roughly) the amount of light at different locations in a scene. Sensitometry tells us what density we can expect from different amounts of light (exposure = luminance x time).
Calibration also allows us to tune measurement devices. Let’s say we want to tune the gain —an exponential increase or decrease in the output—in a theoretical measurement device. Turning the gain knob a known amount will change the relationship between input and output by a known amount. The “gain knob” in photographic plates is development. Longer or shorter development times with one developer or another, at different temperatures, changes the relationship between exposure and density. Sensitometry can be used to calibrate the relationship between “tone curves” (density vs exposure) and development processes (development time, developer type, developer temperature), so the photographer can always achieve predictable results.
In their work on color photometry, William Abney and E. R. Festing developed the knowledge and tools needed to create standardized sensitometers. Abney’s personal focus was on the creation of color sensitometers. Earlier sensitometers, discussed in Orthochromatic Photography Part 2, took a holistic approach. Taylor and Vogel’s sensitometers exposed the plate or paper to white light of different luminances. Warnerke’s sensitometer exposed the plate or paper to the narrow-band emission of phosphorescent paint. None of these systems revealed how plates responded to light from different spectral regions. Abney wrote in 1895, “Some uncertainty still seems to exist as to a simple method of estimating the amount of colour sensitiveness”.1 Abney could have easily focused only on laboratory methods for measuring plate spectral sensitivity, using his color photometer and exposing the plate with different spectral bands. However, he was mindful of the needs of the average photographer who would not have access to scientific equipment. Abney’s goal was to test the sensitivity of plates without the use of a spectrum. “It has always appeared to me,” he wrote, “that a direct reference to the spectrum to obtain a screen was impracticable, even if more accurate, unless special apparatus was available, apparatus which is only to be found in a well-furnished photo-physical laboratory”.2
The guiding principle of orthochromatic photography was that tone values in the print should represent the tonal relationship of colors in the scene. The reference point was white, and all photographed objects had some luminosity less than or equal to white. The range of grays in the image should roughly correspond to the range of luminance in the scene, though at a much-compressed dynamic range. Abney wrote, “if a plate be perfectly colour sensitive, it is evident that the resulting print from a negative should represent the brightness of the light coming through them in exact proportion of their luminosities”.1
Abney was also aware that “The sum of different [plate] sensitivenesses to different simple colours is practically equal to the sensitiveness of the whole when mixed.” This means that a plate’s sensitivity to a mixture of three component rays should be equal to the sum of the plate’s sensitivity to the individual component rays. This should sound familiar from our discussion of Grassman’s Fourth Law and Abney’s Law. Here Abney is stating that Abney’s Law should (theoretically) apply to both the perception of luminance and the sensitivity of plates to luminance. He wrote, “So, if we know the sensitiveness of a plate to all the different parts of the spectrum, we can tell what the sensitiveness is to any portion of it, however much reduced some rays may be compared to others.” The density of any color from a linear combination of different colored bands can be determined using the densities recorded from those three bands. Think of an LCD display. They can create thousands of different colors by simply modulating the amount of red, green, and blue light.
Abney focused on the photography of colored pigments to establish a control condition (rather than landscapes, which are popular but uncontrolled). Relative luminosities vary according to the illumination, but white will always be 100 (the definition of lightness). Knowing that a sensitometer only needed to contain a small subset of pigments to cover the spectrum, he selected red, green, yellow, and orange glasses for his first design. He originally felt that the use of colored glass back-lit by daylight would provide the best sensitometer, but this was difficult to achieve practically.2 He settled on making reflective measurements of the glasses. The process of selecting these glasses involved again the color photometer to measure the spectral luminosity of these colored glasses. Abney instructed the user to “measure as accurately as possible the brightness of luminosity of the light transmitted through them,” and, referring back to the field of view he explored in Colour Photometry – Part 3, he wrote, “that it is well to measure this luminosity when the colours are in small patches, for in a picture, for instance, only small patches of any colour are seen.”1 Remember, the term “measure” at this time in history required visual comparison methods. Abney wanted to make sure viewed patches were within the macular region of the retina.
With the spectral luminances of these glasses in hand, Abney showed that the luminosity of the colored glasses calculated from the intensity curves (transmittance) and the luminosity curves of white light is as accurate as direct calculation of the glass luminosities (Abney’s Law).
As discussed in Orthochromatic Photography Part 1, orthochromatic plates had to be photographed using a special orange screen to filter some of the blue light to which the plates were inherently over-sensitive. Abney’s sensitometer was used to measure not only plate sensitivity, but also the performance of the plate-plus-screen system. His preferred screen was called “Burchett’s Screen.”
Light was also important. The light used to illuminate the sensitometer-plate system had to be the same as used in practical work. Abney wrote, “What we have to do is find a suitable plate and screens which will give in a print these relative luminosities, remembering that we cannot expect to get the luminosities of the colours when illuminated by one kind of light correctly rendered if photographed in another kind of light.” Abney measured the luminosities of the four colored patches under electric light and gas light, but stuck with the electric light as his standard source to maintain the relative luminosities between spectral bands. For example, a ray at the C line is always 21% of a ray at the D line and a ray at the E line is 52% of the ray at the D line. Basically, Abney wanted a light with the same relative output at each wavelength over time (a constant spectral power distribution).
Having settled on a set of calibrated colored filters (known transmittances), a light source (with a known spectral output), and a preferred screen (with a known transmittance), Abney had his prototype sensitometer. The apparatus itself used “properly selected coloured glasses in small squares placed in a row.” Plate spectral sensitivity was estimated by “exposing [the plate] behind such a sensitometer after filtering the light through various coloured screens, and by exposing a scale of gradation on the same plate and measuring the densities of the scale and of the squares.” Again, density measurement refers to a comparison of the resulting negative’s visual density with a calibrated density tone scale.
The prototype sensitometers did not always the same glasses. The combination of white, red, orange, yellow, green, and blue glasses was used in later versions. Abney found only red, green, and blue were essential, but the yellow and orange helped accurately characterize areas of known insensitivity in orthochromatic plates.
In one experiment, Abney calculated the sensitivity of the plate to the colored glasses through different screens by comparing the densities to the step wedge included on the plate. The final sensitivities were normalized to the luminosities of each glass. The goal was to have a plate with sensitivities to the different color glasses as close to one as possible.
The image below shows reproductions of the colored squares on the same plate with different screens. The left column is white, and thus has the most density. This plot helped Abney identify the best screen for color luminance reproduction under electric light, which in this case was the orange screen (the blue, green, yellow, and red patches are most uniform in density).
Abney recognized that even the above exercise, though simpler than using an optical bench, might be difficult for the amateur photographer:
Now it can hardly be expected that an amateur or even a professional plate maker should go through experiments of this nature. In order to avoid this difficulty I have simplified the plan considerably, and I hope rendered the method thoroughly practical, and avoided all necessity for any measurement of density except the preliminary measurements of the luminosity of the light transmitted through the coloured squares.1
In his simplified sensitometer, Abney changed the paradigm of the sensitometry process. Rather than judging the best plate+screen combination by the least difference between color patch densities, Abney first equalized the luminances of the glass squares. The best system was then the one that best maintained the evenness of density. “If we make the brightness of the light transmitted through each colour equal, then a plate perfectly colour sensitive should show equal opacity of deposit under all the squares, when an exposure was made.”
A rotating disk was placed in front of the colored squares to reduce the luminosity of the light reaching each square glass square. This rotating disk, like rotating sectors, relied on Talbot’s law. The disk contained concentric rings of black, the angle of which could be independently adjusted to control the light passing from each square to the plates. Abney calculated the arc length of each ring so that, when the disk was rotated, the colored glasses would all have the same luminance.
After some deliberation, Abney thought the cut-out disk might be too complicated for the average photographer, so he proposed that neutral density filters, prepared from developed negatives, be placed behind the colored glasses to equalize their luminosities. He created the following image of white, yellow, red, and green patches, each with luminance equalized before reaching the plate. It’s clear in this case that the orange screen preserves the densities better than the other screens. This time, Abney also included a gray scale made by exposing the negative four different times.
While developing methods for measuring the physical attributes of color and colored objects, Abney remained aware of the differences between the physical and the psychological. He pointed out how the peculiarities of color appearance influenced perception of luminance. For example, he used his color photometer to answer the question about how to equate the brightness of opposing colors, such as red and green. Abney wrote, “It has been said by the highest authority on colour, Helmholtz, that he could not picture a method by which a red and a green might be matched for brightness”.3 He added, “Supposing we proportionally reduce the light falling on [red and green] we shall see that the brightnesses no longer hold.” If the brightness of red and green are equal under one luminance level, the values may not appear equal if the luminance is reduced.
“To judge, then, of the luminosity of the colours, we must know the intensity of the light which calls them into being. Thus, a picture in which there was red and green might, under bright illumination, show a particular red, as brighter than a particular green, whereas, in a sombre light, the reverse might be the case. It is well known that toward the evening, the last colours which appear vivid to the eye in pictures in a picture gallery are the blues, the reds disappearing early”.3
Color appearance is dependent on illumination and visual adaptation. Abney felt that the main cause for the color differences was the presence of the yellowish macula in the center of the visual field, absorbing blue light. We know today that the macula is not the only factor. The macula is, in fact, a constant. When the illumination changes, there is a proportional change in light passing through the macula. The human visual system does not change its perception of hues at different illuminations, at least within the range of photopic vision. If Abney were testing a light level nearing mesopic (twilight) and scotopic (nighttime) levels, where rod vision starts coming into play, then perhaps some hue shift might be observed for certain colors. In most cases, though, the human visual system adapts to change in illumination.
In addition to its effect on the perception of brightness, Abney compared the measured spectral luminance of sun light (using the color photometer) to the sensitivity of the plate to sun light. He found that the plate showed the greatest response to the violet, blue, and green, known attributes of orthochromatic plates. Therefore, a large portion of the violet and blue should be cut to equalize the plate to the absolute luminosity of sun light. This demonstrates another utility of the color photometer as a method of determining the spectral regions that should be cut for different types of illumination.
Edward Sanger Shepherd (the name Edward was often abbreviated ‘E.’), an early pioneer in color photography and contemporary of Abney’s, also made contributions to color measurement and the measurement of orthochromatic plates.
The goal of orthochromatic photography, Shepherd said, was to “bring the visual and photographic impressions into harmony.” When selecting the correct plate for a situation, the photographer must consider tone reproduction: “The best plate…will be the one giving the greatest number of distinct gradations between these limits”.4 The yellow screen and developer also impacted tone reproduction. The yellow screen functioned to block UV and reduced blue density. The yellow screen might also impact other colors, though to a lesser extent. Developer chemistry also affected how long it took for certain spectral components to appear in the development process.
Shepherd, along with Abney, used scientific measurement to analyze orthochromatic plates, screens, and developers. He created a device to photograph a spectrum on a test plate through different home-made screens, similar to Abney’s color photometer, shown below. A light source was focused on the slit, F. The light then passed through a collimator, C, to a prism, B. The refracted light was focused by a camera, D, on a plate, K. A test screen could be placed in front of the plate and a shutter within the collimator could be opened or closed to expose the plate.
When selecting the light source, Shepherd alluded to Abney’s preference for the electric arc lamp. Shepherd preferred a regulated gas burner over an electric arc lamp because it gave a constant luminance. The downside of the gas burner was the low amount of blue and violet energy. The wavelengths were calibrated by burning “asbestos fibre soaked in lithium, sodium, and potassium carbonates in dilute hydrochloric acid.” These created spectral lines with known wavelengths.
Shepherd cited Abney’s color sensitometer with the four glasses of equalized luminance. Abney recommended the use of neutral density filters, but they had to be custom-made because there were no commercially available neutral density filters at that time. Shepherd and Abney both manufactured their own neutral density filters by developing plates to different densities. The manufacture of neutral density filters and color pigments required a method of calibration and measurement. One could use Abney’s side-by-side patch method for measuring the luminosity of pigments, but as discussed previously, this was impractical for the wider audience. Measuring the density or luminosity of transparent materials required a transparent step wedge (of 20 or so divisions). A rotating disk with concentric rings of different arc lengths could also be used.
Shepherd created a device, shown below, for measuring luminosities and densities of transparent materials. The light, A, enters a box bisected by a wall, H, and interacts with a beam splitter, B. Some of the light is transmitted through the beam splitter, reflected off mirrors C and D, before making their way to a viewing screen, E. The other part of the light reflects off the beam splitter and is directed to the other side of the viewing screen, E, by a mirror, G. The light reflecting off the surface of the viewing screen is modulated by rotating sectors, I.
The type of viewing screen employed by Shepherd was an “Abney Screen,” another invention of William Abney.5 The Abney Screen, he wrote, “is a blackened brass plate having an opening 2 cm wide and 1 cm deep on the optical center line. The opening is filled with a piece of thin opal glass. One-half of the glass visible through the opening…is coated at the back with zinc white paint and, when dry, backed with opaque black paper.” Opal glass is a translucent, diffuse white glass. Light comes to the Abney screen from two sides. A rod, F, at the front of the screen prevented light from hitting the translucent side, while light from the backside passed through the translucent half. An illustration of an Abney Screen is shown below.
Additional glass plates could be added to the beam splitter to reduce the amount of light transmitted through it, thus lowering the intensity of light reaching the backside of the Abney Screen and increasing the intensity of light reaching the front reflective side. The system was calibrated by adding more or fewer glass plates to the beam splitter until the luminance on both sides of the Abney screen was equal. A negative, or other transparent object being measured, was then clipped to the backside of the Abney Screen (shown below). The object absorbed light, making the front-side brighter. The front-side illumination was reduced using rotating sectors until the two halves are again at equal luminance. The luminance of the test object was derived using Talbot’s Law from the setting of the rotating sectors.
This setup was not unlike the operation of analog densitometers used in the mid-20th century. The user had a target with known densities, then calibrated the densitometer using a manual dial until the display read the known density of the target. The only difference in the later models was the use of a more reliable electronic circuit rather than human observers.
Shepherd modified the transmission densitometer for reflective measurements by a slight change in optics, placing the target bi-partite screen at the back of the device, rather than in the middle. This looked more like Abney’s color photometer.
Abney’s earlier sensitometer—four colored glass plates with luminances equalized using either neutral density filters or rotating sectors—required the sensitometer to be nearly in contact with the plate, and that the illuminating light be the same as light used in photography (Abney W. , 1900). In 1900, he created another sensitometer with the added emphasis on determining not just the proper plate+screen for monochromatic color reproduction, but the proper red, green, and blue screens for three-color reproductions. The new sensitometer was made of a disk with concentric rings of different pigments (White, Yellow, Red, Green, Blue, Violet, Black). In addition to simplicity, Abney felt “some sensitometer should be employed which should be independent of artificial light” (Abney W. , 1906).
On each colored ring was a black ring whose arc-length could be adjusted to control the luminance of each pigment. He wrote, “My new sensitometer consists of pigments toned down by a mixture of black.” By “toned down,” Abney was referring to a partitive mixture (mixed by the eye, not physically) with black, not a pigment mixture. Abney measured the luminance of each pigment, then the rings were arranged in order of increasing luminance, with the darkest pigments in the center. He calculated the black arc-length required to equalize the luminance of each pigment. The rotating disk was then photographed. For a given plate, the screen that would give equal densities was selected. He described this principle in a later article:
The principle that I adopted was to secure that all pigments which were in front of the camera should have the same color luminosity of one to three components which make white, so that if (say) a red screen was being searched for, the red component in each pigment should be of the same value; for then the negative, if the screen was correct, should show each pigment has having the same density.2
A simplified illustration of Abney’s new device is shown below. On the left is a rotating disk with concentric rings of blue, yellow, and white (blue being the least luminous and white being the most). As the darkest pigment, blue needed no toning down with black. Abney calculated the amount of black to add to yellow so its luminance would equal that of the blue, and likewise did the same for white. The disk was set in motion and photographed. The ideal plate+screen combination would show all three rings having the same density.
For his three-color sensitometer, Abney used the three-slit variation of his color photometer to calculate the percent of each spectral component (red, green, and blue) to match different colored pigments. He derived color-matching functions* for the three theoretical red, green, and blue screens needed for three-color reproductions. Abney determined the amount of red, green, and blue light from the three slits to match a specific set of pigments, using a yellow and blue-green pigment in his example. He also determined the amount of red, green, and blue light to match white. Using the color photometer, Abney calculated the luminances of each component (R, G, B), which were then added to calculate the luminance of the pigment. Initially, the component luminances were measured against the pigmented color, normalizing it to 100 (e.g. 50 R + 50 G + 0 B = 100 Y), and then scaled against white. For example, if white = 100, and Yellow = 60, then the 50 R + 50 G becomes 30 R + 30 G = 60 Y.
The white, yellow, and blue-green pigments were then set in a disk. Abney calculated the amount of each pigment to be uncovered such that the negative densities would be equal when photographed through red, green, and blue screens. He then photographed the rotating disks through the red, green, and blue screens with transmission peaks roughly aligned to the center wavelengths of each slit. This allowed him to validate that the screens were correctly chosen. The photographs below show the disk when static (left) and when in motion (right). Note the rings on the disk in the right photograph appear to be of equal density.
Abney’s method of estimating the red, green, and blue glasses using slits in the color photometer allowed for the modulation of red, green, and blue luminosities, which was not easy to achieve using actual glasses. James Cadett stated, “This new method of sensitometry was of extreme value, because it gave one the power of making the various colours of any desired luminosity; whereas with glasses, unless revolving sectors were used in front of them, the luminosities could not be varied.” However, the selection of “pure colours” for the pigments would be difficult. Shepherd preferred the method with the four glasses rather than the rotating disks because he felt they were more practical.
Abney’s primary focus in developing his various sensitometry systems was the selection of appropriate plates and screens for monochrome and color photometry. Other scientists before Abney simply needed a method to determine the correct exposure for their plates. Understanding the full tonal relationship was not their primary focus.
Developing the Science of Tone Reproduction
Charles Edward Kenneth Mees and Samuel Edward Sheppard (not to be confused with his contemporary Sanger Shepherd) followed in the footsteps of Ferdinand Hurter and Vero Charles Driffield (known to history as “Hurter and Driffield” or “H&D”). Mees and Sheppard sought to understand fully the relationship between exposure and density for orthochromatic plates. They wrote about Abney’s sensitometer,
The chief objection to the Abney sensitometer is that it does not give a scale of tones but only one tone, and it appears distinctly better to divide up the spectrum into sections and measure the sensitiveness of the plate to each section…Thus we see that the ideal towards which we may aim in colour sensitometry is to have a spectro-sensitometer with which we may expose plates either to a series of pure colours or to a broad band of colors.6
Mees and Sheppard explored methods of obtaining the spectral sensitivity of plates using a full spectrum and using broad-band filters, and of combining the two systems into a general spectro-sensitometry system.
The spectral sensitivity using a full spectrum could be measured by placing a plate sample in a spectroscope and exposing it to the entire spectrum. This was not uncommon. The problem was that prism spectra are not evenly distributed among the wavelengths (dispersion increases from red to blue) and the spectral power of the light source may confound the measurements. For the light source, the photographic community agreed that the light used for testing plates should be diffuse daylight, but daylight itself cannot be used for scientific measurement because it is ever changing. Mees and Sheppard proposed an artificial daylight (a daylight simulator) by filtering an acetylene burner so the spectrum resembled daylight. The CIE adopted a similar illumination standard in the 1930s called Illuminant C, a daylight-filtered tungsten, which was the predominate daylight simulator in the days before fluorescent lighting was available. The acetylene artificial daylight lacked energy in the UV and violet regions of the spectrum and was too strong in the red, but it was the best option at the time. The daylight filter was adjusted by comparing the density of spectra projected onto panchromatic plates taken from daylight and modified acetylene. The acetylene flame used by Mees and Sheppard, illustrated below, was surrounded by “a metal screen B…so as to shield it from draughts and a small metal cone, LL’, reaching to within 3 mm. of the flame and ending in a little window C. The height of the flame should be approximately 35 mm (1 3/8 in.) and two gaps are cut in the top of the hood B with sighting cross wires, which should just cut the tip of the flame.”7 The small metal cone was part of a light regulator, called a Methven Screen, which allowed the passage of a specific quantity of light. The daylight filter placed in front of the lamp was a custom formulation investigated by Mees and Sheppard, with the help of local dye companies8, that ultimately became a No. 79 Wratten (a pale blue with a violet tint).
The photographic plate was placed in a spectroscope with a calibrated wavelength scale and exposed using the filtered acetylene lamp.
There were three possible sensitometry methods using broad-band filters. The first system, like Warnerke’s, exposed the plate to a step wedge. The user indicated the highest number step for which there was some minimum density on the plate. The second system was used by Eder. The sensitivity of most ordinary plates dropped off at around 510 nm, so Eder created a yellow and blue filter with spectral transmittance curves that crossed at 510 nm. The filters were placed in front of a Scheiner wheel (shown below, referred to as a “Sector Wheel”), a solid wheel with a staircase-like section with 23 steps cut away. The arc length subtended by each step differed from its neighbor by a ratio of 1:1.27. The wheel was placed in front of the plate, an exposure was made, and the plate developed. The resulting pattern looked like a step wedge with incremental changes in density. Plate sensitiveness was defined by the smallest arc length that produced a density signal on the plate. The user then calculated the sensitiveness ratio of blue to yellow.
Mees and Sheppard found the two-color test insufficient for plates sensitized using isocyanines, which increased red sensitivity.6 They updated the test for three-color photography by exposing the plate, with Eder’s Scheiner wheel, behind red, green, and blue filters. Exposures for each filter were calculated so the plate received approximately equal luminance after light passed through the filters. Ratios of the sensitiveness between the three filters were calculated. They used the results to fine-tune the formulation of plate-sensitizing dyes. According to Klein, the incorrect ratios between the red, green, and blue filters “are probably more responsible for incorrect color reproduction than that of the theoretically incorrect printing-ink.”9 Klein created his own “Ratiometer” that would expose three sample plates behind three filters. A shutter in front of each filter could be slid to five positions, each with different exposures. The user then determined that exposure for each filter that gave the equal density to other filters. The ratio is the ratio of exposure that give equal density for the three filters (e.g. 5 sec. : 15: sec : 15 sec). The same light had to be used for actual work as for test work.
Mees and Sheppard did suggest a method that might be used to combine full-spectrum measurements and broad-band measurements, though they were not able to complete any experiments with such an arrangement.6
Hurter and Driffield used a discrete sector wheel with a 1:2 ratio (range of light 1:256), similar to Eder’s design. However, producing a sector wheel is costly due to the required precision machining. Some special emulsions are also impacted by the intermittent exposures from the Scheiner wheel, resulting in inaccurate measurements. In the 1870s there were thoughts on how to use a neutral scale in sensitometers. This could be placed in contact with the plate and modulate light instead of a sectored wheel. However, neutral scales were difficult to manufacture without any color tint. It was not until 1910 that Emanuel Goldberg suggested a manufacturing process using a dyed lampblack in gelatin between two plates. He later switched from lampblack to exposed silver grains. Step wedges became the standard for sensitometers into the 20th century. (see Buckland’s 2006 book, Emanuel Goldberg and His Knowledge Machine,10 for more information about Goldberg).
Conclusion
The development of orthochromatic photography and the measurement techniques—plate sensitivity, spectral luminance, spectral reflectance, and other important factors—that arose in parallel, were essential in the development of monochrome and color photography and printing in the 20th century. The validity of an experiment or data set is often judged by its usefulness for future researchers. Photometric and density measurement techniques of the late 19th and early 20th centuries were in their infancy. They were developed to help photographers and photographic suppliers better communicate technical specifications and use procedures. There was no standard language of color they could speak. They needed numbers. They needed standards, though none existed at the time.
David McAdam, an eminent color scientist and key figure in the development of CIE colorimetry in the early 20th century, did not look fondly on the contributions of Abney’s work: “With the exception of Abney’s Law, his work had almost no influence on the subsequent development of colorimetry. Not even his luminosity data were accepted as reliable by subsequent colorimetrists.” (Cohen, 2001, pp. 155-156). It may be true that his data, based upon human judgement, did not meet the needs of color scientists with electronic measurement systems. However, his contributions, and those of his peers (Shepherd, Mees, Sheppard, among others) can still be seen in the color measurement instruments and color science research of today. Abney and Festing helped define the measurement of lightness and spectral reflectance. Mees and Sheppard, following Hurter and Driffield, outlined the principles of color sensitometry and were among a group of scientists to begin specifying standard sources and illuminants, such as Illuminant A (though “illuminant” was not a standard term at the time).
It is in our best interest to learn from the experiences and thought processes of our predecessors, regardless of how they are viewed in hindsight. Abney and Festing included an entire discussion of their thought process in their papers, presenting ideas that worked and ideas that did not. And, at the end of every journal article from the period, a dialog between the authors and their peers was published so the public could gain insight into not only the minds of the authors, but into that of the scientific community. Progress is driven by the dialog and constant reinvention, not the individual achievements. Perhaps this is the most important lesson we can learn from our forefathers.
- *Color matching functions basically tell you what amounts of red, green, and blue light are needed to match the color of a given spectral band.
Disclaimer
This article was written by Brian Gamm in his personal capacity. The views, thoughts, and opinions expressed in this article belong solely to the author, and not necessarily to the author’s employer, organization, committee or other group or individual with which the author has been, is currently, or will be affiliated.
References
- 1.Abney W. Orthochromatics. Colour Sensitometry. . The Photographic Journal. 1895;19:328-342. https://www.google.com/books/edition/_/2Rw_AQAAMAAJ?hl=en&gbpv=0
- 2.Abney W. How to Make A Sensitometer. American Amateur Photographer. 1906;18:477-479. https://www.google.com/books/edition/The_American_Amateur_Photographer/u55RAAAAYAAJ?hl=en&gbpv=0
- 3.Abney W. Orthochromatic Photography. Journal for the Society of the Arts. 1896;44:587-597. https://www.google.com/books/edition/Journal_of_the_Royal_Society_of_Arts/oBFGAQAAMAAJ?hl=en&gbpv=0
- 4.Shepherd ES. The Scientific Translation of Colour into Monochrome. The Photographic Journal. 1898;22(11):347-359. https://www.google.com/books/edition/The_Photographic_Journal/_xs_AQAAMAAJ?hl=en&gbpv=0
- 5.An Abney Screen for Measuring the Opacity of Negatives. In: Illustrated Catalogue of the Royal Photographic Society’s International Exhibition at the Crystal Palace. The Royal Society; 1898:198. https://www.google.com/books/edition/Illustrated_Catalogue_of_the_Royal_Photo/2EMkDdtpdCAC?hl=en&gbpv=0
- 6.Mees CEK, S. S. The Estimation of the Colour-Sensitiveness of Plates. The Photographic Journal. 1906;30:110-131. https://www.google.com/books/edition/The_Photographic_Journal/SR0_AQAAMAAJ?hl=en&gbpv=0
- 7.Wall E. Elementary Sensitometry. American Photography. 1923;17:298-309. https://www.google.com/books/edition/The_Photographic_Journal/_xw_AQAAMAAJ?hl=en&gbpv=0
- 8.Mees CEK, Sheppard S. On the Sensitometry of Photographic Plates. The Photographic Journal. 1904;28:282-303. https://www.google.com/books/edition/The_Photographic_Journal/_xw_AQAAMAAJ?hl=en&gbpv=0
- 9.Klein H. The Importance of Correct Ratios in Color Photography. Inland Printer. 1907;38:713. https://www.google.com/books/edition/The_Inland_Printer/Z4giAQAAIAAJ?hl=en&gbpv=0
- 10.Buckland MK. Emanuel Goldberg and His Knowledge Machine. Libraries Unlimited; 2006. https://www.google.com/books/edition/Emanuel_Goldberg_and_His_Knowledge_Machi/QCddw5cVjVgC?hl=en&gbpv=0&bsq=Goldberg%20lampblack%201910
