XIX·XXI, A tribute to the work of Charles Wheatstone and William Henry Fox Talbot
1. Introduction – On June the 21th of 1838, Charles Wheatstone presented his paper Contributions to the Physiology of Vision. Part the First. On some remarkable, and hitherto unobserved, Phenomena of Binocular Vision (9-WHEAT) on the Royal Society, about the priciples of observing the third dimension from bidimensinal draws. Short time later, on 1839 and 1840, the first reasonably stable photographic procedures were also presented, the Daguerreotype from Louis-Jacques Mandé Daguerre and the Calotype of William Henry Fox Talbot. From the very early time, Charles Wheatstone was deeply interested on the new photographic techniques in order to obtain stereoscopic images, allowing the observer to go a bit beyond the bidimensional representation (10-WHEAT) and (11-WHEAT). Because of the work from John Brewster and others, the stereoscopic photography experimented an almost immediate success, being one of most employed applications of the new photographic techniques (3-METH).
In parallel to those and other applications, a field of research and growing of these new techniques was focused on the procedures to offer a better life expectancy of the photographic imaging. Beside the changes proposed by new processes and some advances in chemical residues elimination, wich caused the degradation of the on paper pictures, the work of Talbot on photogravure was, with the technology available at this time, one of the best contributions at this photography life expectancy. In his patent Nº565, entitled Improvements in the Art of Engraving and registered by Talbot on 1852, it is described the procedure to translate the pictorial information of a positive photographic material onto a metal plate etched by acid. The introductory text said: “The patent consisted of producing a photographic image on a metal plate, using this image as a resist to control the etching of that plate, and then printing the resulting plate using a conventional printing press and standard printer’s ink” (8-SHAAF). Depending on the ink and paper employed, the life expectancy of the printed pictures would be at least as long as the traditional gravures printed on the past centuries. The photographic image over the plate was obtained exposing under the Sun light a layer of bichromated gelatin through a positive calotype paper, being previously waxed to transparent it. The plate was of steel and the etching performed by a solution of Platine Chloride.
Talbot introduced diverse and progressive improvements to the process, initially called photographic engraving. One of most important was the use of a piece of textile fabric during the exposure in order to screening the image. This screening allowed for a better ink retention in the shadow extended areas during the plate wiping. Talbot named those rag pieces as photographic screens or veils.
On 1858 he registered a second patent, the Nº875 with the same title Improvements in the Art of Engraving (8-SHAAF). Nevertheless, in this case he changed the name of the resulting print as photogplyphic engraving. Additionally, adopted the use of resin powder aquatint in substitution of the fabric screen, copperplate and Ferric Chloride (III) as etching solution. This system was the higher state of development achieved by Talbot while it still encompassed a certain difficult to preserve a complete tonal range in the final print, mainly in the shadows and mid tones. It was on 1879, two years later Talbot passed away, when Karel Klic introduced a definitive method modification taking the idea of a temporal gelatin support stated by Louis de Poitevoin for the Carbon Transfer technique, which was later developed by Joseph Swan. He named the process as photogravure and quickly was called as Talbot-Klic method (https://youtu.be/jozS7qKb7Co).
But there is also another link between the advances early mentioned of the stereoscopy and photogravure. From the epistolary relationship between Talbot and Wheatstone, based in common interests as electromagnetism and electric machines, it can be derived that on 1840 Wheatstone experimented with his stereoscope using glass plates of images taken by Talbot (10-WHEAT). Later on 1858, there is an offer from Wheatstone to provide Talbot with glass plates helping him in his experiments on photogravure. Following with this relationship between stereoscopy and photogravure, on the same 1858, Wheatstone wrote to Talbot: “… I think one of the most immediately profitable applications of your new art <3> would be to the production of stereoscopic pictures, for which there exists now an immense sale. Upwards of 3000 glass slides for the small stereoscopes have been published in Paris which are sold at prices varying from 8s/ to 12s/ each; even these pictures, already existing prod reproduced by your art they might be sold at 6s/ per dozen each, and would, I have no doubt meet with a considerable sale. There would be no expense beyond the transfer of the pictures and printing of the plates. My large stereoscope, far superior as it is to the others, has never become popular on account of the expense of the pictures. Were they reproduced by your method, I have no doubt that if some optician <sic> to take it up he would find it to answer his purpose.” (12-WHEAT)
There is no evidence about an answer from Talbot to this proposal. Until today, neither has been found any photogravure of an stereoscopic pair among the catalogued part of the extensive work of Talbot. The answer to a question proposed to the professor Larry J. Schaaf, Director of the William Henry Fox Talbot Catalogue Raisonné, from the Oxford University, about this matter, was: “… all the known correspondence between Wheatstone and Talbot is posted. I know of no notes where he attempted to use both halves of any stereo, apparently this did not interest him. There is a very large number of uncatalogued and largely unexamined photogravures, so finding a pair is not impossible.”
We can today imagine this epistolary relationship between Wheatstone and Talbot as the footprint of a path to follow. Relying on that, the XIX·XXI project features the edition of three heliogravures (photogravure on copperplate) of stereoscopic images. Fossils of Ammonoidea, Echinoidea and Gastropoda have been taken as a photographic subjects, being in turn the footprint of a common past. In the final step of the project, the footprint of the copperplate on the paper don’t dare to represent the end of the path, but only one more of the footprints contributing to close the circle of complicities between stereoscopy and photogravure. Also serve this work as a simple tribute to the work developed by those pioneers of the respective techniques.
2. Image Capture – From the several options available and with the goal to work at the same technical level existing at the Wheatstone and Talbot time, the so called side by side stereoscopy it’s been chosen. In this method, the two necessary images of each subject, taken sequentially with a lateral displacement of the point of view (Fig., 1), are shown to the correspondent left and right observer eyes. In order to isolate the image assigned to each eye, an instrument called stereoscope is used.
The Fig., 1 shows the lateral displacement applied to the camera for the respective left and right pictures. This separation, called stereoscopic basis, can take diverse magnitudes depending on the distance from the camera where the subject is placed. The figure of 60mm used in this case will be further reasoned. Note as in the example the respective sides l and r of the subject O are uniquely visible for one of the camera positions, L or R. This disparity of the hidden or visible parts of the subject, allows to the observer vision to detect the third dimension when the pair of images is seen through an stereoscope. The third dimension is then perceived from a bidimensional picture. From this scheme can be also derived that in order to achieve the desired effect, this lateral displacement must be, as far as possible, the only difference between the pictures of the stereoscopic pair.
In order to reduce to the minimum the position errors between the subject, the camera and the respective left and right pictures, the capture setting employed has a series of properties being described in the next paragraphs. The camera body is a SONY Alpha7II provided by a Nikon Micro Nikkor 55mm f/3.5 lens. Being zenith the chosen point of view, the camera is attached to a reproduction column that ensures a parallelism between the respective planes of camera sensor and subject support. The mounting system allows for micrometrical displacements along a vertical axis, while the lateral displacement is achieved by simple liberation of the Arca Swiss type clamp (Fig., 2).
All the available displacements ensure the parallelism between the above mentioned planes. The vertical micrometrical displacement provides the focusing of diverse size and thickness subjects both maintaining the lateral magnification provided by the lens helical focusing ring. The lateral displacement provides the necessary stereoscopic basis between the pictures of the pair. The ensemble camera/lens can also travel along a vertical axis through the mechanisms of the reproduction column.
The three fossils chosen for the project are different in size. Then, if the same relationship between figure and background want to be maintained in the final prints, it would be necessary to change the camera to subject distance for each of them and this would provoke in turn changes in lateral magnification, depth of field and perspective perception to the observer. Additionally and given the size of the fossils, it would be necessary for some of them to close up the camera to the subject at a distance shorter than the so called human comfortable vision distance, being of approximately 350mm.
This distance, determined by the focus on capabilities of the human vision system, generates a perception of perspective being the closer to an object that the naked eye can observe with sharpness and without external optical aid. From the point of view of an observer with healthy or suitably corrected vision, both the shape of the objects as the relationships of their own dimensions will be perceived as a consequence of this distance. Any close up position shorter than that needs of an external optical aid and this changes in turn the perspective of observation. From all that can be derived in turn two more questions at least:
- Even modifying accordingly the stereoscopic basis, it is not so clear since several authors which is the perception the observers would have from the pictures of an object located at such a distance, that they haven’t could seen in the reality.
- The human visual system observe at this distance of 350mm or longer those objects not smaller enough to require the help of an optical magnifier.
Given that the three fossils chosen for the project do not show any difficult to be observed by the naked eye at this distance of 350mm, the pictures have been taken at a similar distance, allowing in turn for a perception of perspective very close to the standard vision. The actual distance of the camera to the subject was of 400mm, slightly longer than the above cited, but providing a bit more space for the lighting setting up. This distance allows for a stereoscopic basis equal to the average separation of human eyes of about 65mm. With this stereoscopic basis it is not taken into account the human eye convergence. This convergence can be simulated by the camera rotating its axis accordingly for each one of the L or R pictures, but this in turn introduces in the pictures a Keystone effect which must be corrected later by digital image processing. A common intermediate procedure is to reduce a bit the stereoscopic basis but maintaining the parallelism between the respective sensor and subject planes (1-LIN). In this case, the stereoscopic basis has been reduced to 60mm. With those parameters already decided, some calculations had been done to control the depth of field available:
- With a lens of 55mm of focal length and an object distance of 400mm, the image distance is of 57.14mm.
- The quotient between the respective image and object distances, gives a lateral magnification of m = 0,14 for this situation.
- Provided that with the camera sensor employed the limit by diffraction is stated at f/16, the depth of field available for this diaphragm number is calculated. The result is DF=63.8mm (4-MIT). The fossils thickness does not exceed this value in any case. Then, the images can be taken with a single shot, avoiding the need to apply the focus stacking technique.
A last verification lend to ensure that after cropping the respective images to the desired subject to background relationship, there are still a number of available pixels for the printing needed size. This is specially necessary for the smaller fossil, demanding the biggest cropping by report to the original image. In this work, the stereoscopic pair it is foreseen to be observed through the OWL Stereoscope from the London Stereoscopic Company (Fig., 3) (2-LON). Being the recommended separation of homologue points for this stereoscope of 70mm, the images of the stereoscopic pair must be printed at a size of 70x70mm or less. From this size and the output resolution on the image to be sent to the print (288ppi), it is easy to calculate than the minimum number of pixels needed is of 795x795pix for each picture composing the stereoscopic pair. As the cropped picture of the smaller fossil still measures 2534x2534pix in size, there is not any constraint on this matter. Therefore, the three pictures have been taken with the above described camera set up. Finally, the original pictures will be preserved at its original size allowing for further applications. The files to be sent to the printer in order to generate the positive transparencies intended for heliogravure, will be downsampled from this original files to the necessary number of pixels.
3. Lighting Scheme – The aesthetic approach for the pictures of this work, would be inscribed at a medium distance between the mere documentary description and the pictorial image. While at the very early times of Photography the mere reproduction goal was very common, a development of its own language was quickly adopted. In this work and in order to describe the relevant characteristics of the fossils, a zenith point of view is chosen. This point of view is also the most commonly employed to observe museum and/or collection specimens. Nevertheless, in order to avoid an excessive asepsis in the final result, a textured mineral background is added. This texture, beyond its complimentary aesthetic contribution, represents a continuity with the material from what the fossils are made.
Contributing to a correct description of the subjects volume, a diffuse lighting scheme is used. This allows for a smooth shadow borders. This smoothness avoid an excessive prominence of the shadow competing with the subject itself and do not provoke a conflict with the background texture. The diffuse light source is a translucent plastic sheet positioned very close to the subject. Its relative size to the subject ensures the evenness of the general illumination.
In the Fig., 4, the complete lighting scheme is shown. An electronic flash strobe is placed behind the diffuser. The distance from this flash to the diffuser determines the light diffusion and, as a consequence, the shadow border projected by the subject. The height of the flash drives the visibility of the subject texture and the length of the projected shadows. Finally, a corrugated aluminium sheet acts as a light reflector controlling the lighting contrast. Its distance to the subject allows to control the persistence of texture in the shadow areas. For any desired contrast ratio in the final image, the lighting contrast ratio must be maintained always a bit below. The later digital image processing will provide the opportunity to rise this initial contrast, while to do conversely wouldn’t be always possible.
The Fig., 5 shows the left image of the Ammonoidea stereoscopic pair. There can be observed the background texture, the shadow length and the presence of texture into the areas in shadow. Those parameters can be modulated as desired by means of the above described distances and angles. Taking images for stereoscopic pairs at a relative close up distance, there can be observed some lighting changes between the couple of images. This is caused by the different point of view used on each respective image. As a general rule, those differences will be more evident as higher is the specularity of the subject materials. In this case, while the fossils do not show relevant differences, they are fairly present in the background (Fig., 6). Different materials have diverse specularity. While it could be supposed as a constraint, the observation of the stereoscopic pair through the stereoscope shows as those differences are perfectly fused by the brain of the observer. In fact, these differences in tone and specularity are also present for the respective left and right eye in a naked eye observation. Therefore, those changes in tone aren’t fixed in the post-production. Both the raw files and the final files processing is performed for the whole stereo pair.
4. Digital Image Processing – The digital image processing sequence is as follows:
- The raw files have been processed in Adobe Camera Raw applying a previously prepared settings profile intended for pictures taken with this camera and lens (7-MIT).
- When processed, the images are saved as .psd files and coded as L or R.
- Both L and R files are opened as layers in a new image file. A white Background Layer is also created.
- The L and R layers are aligned by reference to a common subject property in the center of the picture. Applying the Difference Mode to the upper layer helps in this alignment.
- The image file is then cropped to a 1:1 size ratio with the option Delete Cropped Pixels activated. This cropping determines the subject to background relationship.
- The Canvas Width is adjusted to a 2xP size, where P equals the number of image side pixels resulting from the former cropping.
- A number of pixels is added to the image canvas providing the separation needed at the center of the stereoscopic pair. This number is derived of the needed space and the output resolution for the printed positive transparency intended for heliogravure.
- The layers L and R are respectively positioned at the extremes of the image canvas.
- Two rough selections of each fossil are saved and coded respectively as L or R.
- Taking those saved selections and their inverses, Adjustment Layers of BW Conversion and Curves are created on top. These layers allow for the adjustment of the BW conversion and general contrast in a separate way for the fossil or the background. The layer masks are smoothed to avoid artefacts. If there is some remaining of the original color in the borders of the layer masks, a general on top Hue-Saturation adjustment layer with 0 Saturation will eliminate it.
- A merged layer is generated on top in order to apply the edge sharpness improvement.
- A second merged layer will serve to fix small differences of texture between the two images of the stereoscopic pair.
- After save de changes, a new file is saved as flatten TIFF without compression and 8bit. This new file is downsampled to the size intended for printing the heliogravure positive transparency. The printing size must preserve the necessary separation between homologue points of 70mm, as is indicated for the use of the OWL Stereoscope from the London Stereoscopic Company.
- The file is laterally inverted and mounted on a stencil intended to print positive transparencies for heliogravure (Fig., 7).
This stencil incorporates a grayscale of eleven steps at right. This grayscale is used to control the etching progression when the copperplate is immersed in the Ferric Chloride (III) bath. A second utility is to be used to measure the final print reflected density. A plot of the density of the eleven steps against the gray value of the sequence will inform about the linearity of the final printing result, being this linearity a link with the original digital file image tones. Finally, the density measurement provided by the Black (0) step will also inform about the matching or not with the maximum density expectancy for the ink used.
Note as the inkjet printer ink combination has a yellowish hue. In this case, this is the better ink combination found in order to perform the best blocker to the UV light employed. Any UV light source should be calibrated on this way (6-MIT). With the positive transparency already printed, the procedure follows as is usual in heliogravure or photogravure on copperplate (5-MIT). This work is composed by three prints with the correspondent stereoscopic pairs. They are entitled as Ammonoidea, Echinoidea and Gastropoda, taking those names from the Class or Sub-class of the three fossils shown in the respective pictures.
5. Edition – The heliogravures have been printed in a number of three, plus one A/P (artist proof). The Fig., 8 shows one of the final heliogravure prints. The prints are entitled, signed and numbered in roman figures (I/III, II/III and III/III). Each print incorporates a dry embossing with the title of the project, XIX·XXI. The paper is Saunders Waterford Cold Pressed (425g/m2) and the ink Gamblin Portland Black. The collection of three different heliogravures, a print with a brief project statement and an OWL stereoscope from the London Stereoscopic Company are boxed in a leather case provided with magnetic closure (Fig., 9).
Figure 9 (click on any picture to access to a slideshow)
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