Reproduction of Photogravure Prints

Cu_29_65_Gris_96Introduction. As in other fine art disciplines, one useful aid to the own progress in photogravure is the critical contemplation of the artwork of other artists, successful or not, famous or not. Although the better valuable way to do that is a direct and alive viewing, in those days of Internet connection, we have also the ability to look to a lot of fine art reproductions from other artists. This possibility widely spreads our capability to know styles, paper-ink combinations, finishing techniques and many more aspects about a given artist work. Conversely, other people like artists, curators or potential customers can look at our artwork if it is available on line.

Nevertheless and beside the intrinsic limitations of on screen viewing, there is another drawback compromising our judgement on a given work. The quality of the print reproduction is a crucial aspect that limits the trueness of what we are viewing. Additionally, this original quality level can be modified to a lower range at several different stages:

  • The reproduction system comprising:
    • The lens and camera sensor respective qualities. The lens must be free of distortion or conveniently characterized in order to be fixed by software at raw file level.
    • The type of lighting source. Color temperature and raw file profiling is very important in order to preserve the correct color reproduction. When it is possible, the best option is the flash strobe used in professional photography.
    • The lighting scheme (quality and direction) aiding to enhance or hiding the print textural properties.
    • The processing of the reproduction digital file.
    • The final file format and compression used in order to be able to upload the image to the web.
  • The changes introduced to the properly processed image file by:
    • The system to create the web site where the image is visualized by the Internet users (Dreamweaver, WordPress, Blogger, WebSiteBuilder, etc.). Each of those systems provides different ways to storage and show images in a web site.
    • Internet servers or storage providers. Most Internet providers use some kind of image compressors in order to save server space. This image compression is done after the processing performed by ourselves.
    • The configuration of the web-browser used by the final viewer. Each web-browser (Firefox, Chrome, Safari, Explorer, etc.) uses its own system to show images and not all web site configurations and settings are compatible with all web-browsers.
    • The Video Card of the computer where the image is viewed.
    • The computer display resolution and brightness dynamic range. With computer displays above the mid range level, the most important difference in viewing conditions is the actual size of the image in the screen. As the file in the server has a fixed number of pixels, the image can take a notable difference in size depending on the given display resolution. Because its high resolution rate, Retina Displays from Apple show the images near half size than the majority of standard computer displays. Some web-browsers, in turn, modifies the displaying conditions to fill the screen with the image.
    • The computer display settings. Most users set its display by default, but the size of the contents is very easy to modify with keyboard commands as <Crtl>+ or <Crtl->.

In spite of the steps we have not under control, at least in a complete way, the reproduction work, the digital file processing and the generation of the version to upload to the net, are our responsiveness. These are, therefore, the subject of this post.

Reproduction system. From the point of view of the perspective and given essentially flat subjects as photogravure prints are, it is not important the camera-print distance. The better and comfortable reproduction system is a reproduction column allowing for a correct horizontal levelling of both the camera and the print. This ensures a perfect parallelism between the print and the sensor planes and hence, no perspective distortion. If the print is in a vertical plane, attached to a wall or vertical stand, there is very difficult to ensure the perfect parallelism between the print and the sensor planes. Conversely, the proposed reproduction column allows the easy levelling of both (Fig., 1).

D610_Repro_ReedsNo4_MkOf

Figure 1. Photographic reproduction set up. A Nikon D700 camera body equipped with a Micro-Nikkor 55mm f/3.5 lens, a right angle viewer and a two axis level (click on the image for an enlarged view).

For Internet purposes, almost any medium and high end level digital camera can provide a very fine reproduction in terms of spatial resolution and color fidelity. The better option is to capture a raw file and process it in order to obtain a linear tone reproduction avoiding any color bias. It is important don’t forget that the goal of the reproduction is to show the print tone scale as better as possible. With this kind of cameras, there are no special problems because any photogravure print encompasses a dynamic range wider than the camera capabilities.

Lighting System. The lighting system is also of great importance in the way to ensure the realistic reproduction of the paper texture, the ink thickness and the plate embossing. Although the classical lighting scheme for flat artwork reproduction is a couple of light sources, one on each side of the artwork and at 45º of its surface, this system provides a flat illumination that tends to destroy the above listed print properties. Light coming from both sides counteracts each other and the local texture shadows are almost eliminated. The result is that any texture present in the print is prone to disappear.

The Fig., 2 shows a comparison of the results coming from two lighting schemes. At left, the print is illuminated from both sides with two flash strobes equipped with white diffusers. At right, the same print is reproduced using a solely flash strobe following a diagonal axis from the upper-right to the bottom-left corner. The differences in the amount of texture presence are obvious. The reproduction placed at right shows clearly the plate embossing characteristic of gravure prints. This embossing relates immediately to the kind of print we are looking at and provides a sort of volumetric perception in the viewer.

ReproComp_ReedsNo4

Figure 2. results comparison between the two lighting schemes described in the text. At left, two diffused lights, one on each side; the plate embossing and the paper texture are almost disappeared. At right, one diffused light at 45º of the print surface and following an axis from the upper right to the bottom left corner; the plate embossing and the paper texture are now clearly visible, preserving the actual aspect of a photogravure print. The series notation, title and signature are also better visible (click on the image for an enlarged view).

As things are never so easy, the second image is not the simple result of the camera capture. While the proposed system, with an unique light source, is perfect in terms of texture reproduction, it lacks in illumination uniformity (Fig., 3).

ReproTexture_ReedsNo4_NoCompensated

Figure 3. Image coming from the raw capture which shows the lack in illumination uniformity caused by the use of only one light fixture. The illumination axis is clearly visible from the upper right to the lower left corner.

Digital Image Processing. As have been previously commented and shown in the Fig., 3, it is necessary a compensation for the lack in illumination uniformity. The good news is that nowadays we have digital image processing to fix this difference in illumination. Photoshop to the rescue! To do that, a Curve Adjustment Layer is added on top of the reproduction image. This layer is adjusted in such a manner to lift the gray value of the bottom-left corner until reaches a value equal to the original upper-right corner. As the Curve affects now the entire image, it is necessary to add a shade in the Layer Mask that controls the area of affectation. The complete procedure in Adobe Photoshop is shown and explained in the following video. My personal preference is do not completely compensating the difference in illumination. I prefer to keep some amount of illumination gradient that, in my opinion, does not compromise the vision of detail in the print, while retaining the feeling of to be viewing to an object and not to a flat sheet of paper (See the comparison in the Fig., 2).

On line file. The preparation of the file that we will show on line can be accomplished attending to several aspects. One common decision to be taken is the size the image will measure at the display of the on line viewer. Few years ago, this was an easy calculation. Taking an average resolution for the majority of computer displays of 72ppi, we need so many pixels as the number of inches in size we have decided multiplied by this resolution number. As an example: If our print image must measure eight inches wide when viewed in a computer display, we need a 8inch x 72ppi = 576pix wide file. In this way, we can control  the size the image will be seen.

Nowadays the decision is more complicated. Current available displays exist in a variety of sizes and resolutions, from little, medium and big mobile phones to professional digital image processing displays, with a lot of in between tablets, laptop and desktop computer displays. Additionally, this variety of sizes is combined with several spatial resolutions. Beside that, the exhibition platforms and the web browser offer even more possibilities of displaying the images in sizes that can vary from the original spatial resolution up to several zoom-in or zoom-out, controlled or not by the user.

All that drives to a complete uncertainty about which is the size our print image will take when viewed by an Internet user. In order to constrain this uncertainty, we can prepare the print images for a given Internet media and a given display or displays. My own experience shows that the better option is to show the work in a platform under control, as WordPress blog, Blogger blog, etc. After choose a platform, we can experiment with this platform and a given web-browser in order to analyse how the print image looks with the several options the platform offers. After this analysis, we can decide how many pixels must the image contain to be seen at a given size under well defined conditions. At least, we can show our work in a concrete way when the actual art work is not available. It is important too to realize that all these criteria will change as the technology changes.

Conclusions. In spite of the difficulties that can be derived from the previous discussion, do not forget that, in some cases, a judgement about our work is a direct consequence from the Internet viewing. It is not matter if we are not interested in to acquire new photographic skills, if we do not feel able to acquire it or do not have the necessary equipment. Those recommendations can help someone to commission the work to a skilled professional photographer. Even more, for a given professional assignment and because we know the actual possibilities, we can also judge if the photographer’s work is at the level our artwork deserves.

Posted in Early Photography, Heliogravure (english / français), Photography, Photography Technique | Tagged , , , , , , , , , , , , | Leave a comment

Perdre el tren

SocialNetworks_UserInterfacesFa dies que hi dono voltes. Des de que vaig arribar a l’edat de la jubilació, he tingut un seguit de propostes de retrobament amb gent que, per diverses circumstàncies, feia temps i fins i tot molts anys que no veia. Reps un e-mail i al cap de poc dies estàs sopant amb companys del primer treball als quinze anys. Es comença per l’inevitable reguitzell de “te’n recordes quan…?” Després cadascú posa als altres al dia de la seva trajectòria vital i al final de tot, hi ha casos en que els cinquanta anys que han passat pesen massa com per tornar a connectar, mentre que amb altre gent sorgeixen noves complicitats.

També hi ha situacions no tant agradables. Aquesta vegada l’e-mail és d’un company del Servei Militar. Quedes per anar a sopar i abans de les postres estàs fins al cap de munt del relat fatxenda d’algú que si mai havia tingut escrúpols, els ha ben perdut pel camí. Ha fet calés i compra pisos a base de saldar el deute amb el banc al que alguns no poden fer front. Quan insinuo, tant educadament com puc, que potser hi ha un conflicte d’ètica en aquesta mena de negocis, em respon que “Hi ha massa gent que estira més el braç que la màniga” i es queda tant ample. En aquest cas i per tal de no arriscar-me a una altre proposta de trobada, li faig saber que, per mi, els més de trenta anys que han passat sense saber res l’un de l’altre han de significar forçosament alguna cosa. Així que fins d’aquí a trenta-cinc anys més, en el cas improbable que tinguem salut i esma d’anar a sopar plegats.

Altres retrobaments son forçats per persones amb qui hi va haver algun desavinença i d’aquí el distanciament. Que algú vulgui escurçar aquestes distàncies és una prova de generositat i sovint, un alleujament d’allò que sabem que hauríem de resoldre però no trobem com. També en aquests casos et pots trobar amb una persona ben diferent de la que recordes. No només pels canvis que imposa l’edat, sinó sobre tot per les vivències que cadascú ha tingut fent el seu camí. Quan el canvi no t’agrada del tot, et consoles pensant que l’altre també et veu diferent a com et recordava i no necessàriament en positiu.

Tot plegat és un exercici de socialització que mai va malament. És gent que en no pertànyer al teu cercle més habitual, et parla de coses que no et son tant properes i moltes vegades t’explica realitats que no coneixes perquè no formen part del teu paisatge. Així doncs, benvinguts e-mails, que a tornar a tallar la comunicació sempre hi som a temps. De totes formes, no és ben bé d’això del que volia parlar. El que fa dies que em volta pel cap és que totes aquestes persones, per edat, son d’una mateixa generació, la meva. El cas és que al menys en el meu cas, hi ha un percentatge força alt d’ells que tenen reticències a tot el que s’anomenen les TIC (Tecnologies de la Informació i la Comunicació). Tot i que atenent a la mida reduïda de la mostra, l’estadística és poc significativa i segurament no extrapolable a la població en general, un noranta per cent d’ells utilitzen les TIC gairebé com una imposició i sense cap entusiasme.

Frases com “Avui encara no he mirat el correu”, indiquen que mirar el correu és per a ells un acte que potser es fa una vegada al dia i no necessàriament cada dia. Un acte en el que cal pensar-hi, dedicar-hi un temps i també un espai, el de l’ordinador. Això vol dir que encara que tinguin un smartphone, no hi tenen el correu configurat o no saben com utilitzar-lo. Correus contestats quan ja quasi no recordes que el vares enviar. Son molts els que no tenen perfil a Facebook i tampoc a Twitter. Uns pocs han traspassat el llindar dels SMS per aventurar-se al WhatsApp. Algun cas extrem es sorprèn quan el banc li comunica que a partir d’ara, haurà de consultar els moviments del compte a la pàgina web de l’entitat o a la corresponent aplicació per telèfon mòbil.

No vull fer cap mena de judici. Molt menys criticar les persones i les seves dificultats per adaptar-se a les TIC. Però les TIC han vingut per quedar-se. Entre moltes altres propietats, les TIC tenen una gran capacitat de mutar en versions millorades cada vegada més de pressa. I el que també és cert és que aquestes persones de la meva generació tenen, tenim, una esperança de vida que a molts de nosaltres ens ha de permetre veure encara canvis més substancials. Sobre tot en la forma com els avenços tecnològics afecten i seguiran afectant les nostres vides. Cal doncs fer-se a la idea i estar receptius.

El tren de les TIC va passar per l’estació de les nostre vides ja fa uns quants anys. Alguns el varen agafar per simple curiositat. Uns altres perquè la feina els hi va obligar. Uns més perquè sempre hem estat interessats en els avenços i el dia que els ordinadors varen passar a dir-se “personals”, ho vàrem interpretar com una crida a cadascun de nosaltres. Això no ens converteix necessàriament en un addicte ni en un freaky. Els fem servir, ens ajuden a treballar, a distreure’ns i també rebutgem aquells aspectes que o no ens convencen o no ens interessen. Però pels que no varen agafar el tren, aquest cada vegada és més lluny. Potser al principi no anava gaire de pressa i encara hi haguessin estat a temps amb una corredissa i la corresponent esbufegada. Però ara el tren ha agafat velocitat i segueix accelerant.

El problema de tot plegat és el risc d’acabar adquirint, sense voler-ho, un cert grau d’analfabetisme social. En el sentit d’Albert Camus, convertir-se en un estrany. Ciutadà de ple dret, però desplaçat, aïllat. Gabriel Jaraba parla al seu blog, en un magnífic article titulat El éxito de Pokemon Go o el punto de no retorno en la vida móvil, sobre la recent aparició al mercat de la Cacera de Pokemons i el reguitzell d’opinions i comentaris, positius i negatius, que ha provocat als mitjans de comunicació. A banda del tema central de l’escrit, una observació que m’ha semblat especialment significativa és la supervivència de la Ràdio en fer-se mòbil. Ja fa molts anys amb els aparells portables basats en la tecnologia dels transistors i ara amb els smartphones.

La mobilitat és un dels trets més importants de les TIC. No només en el sentit que els dispositius son mòbils, també en que ens podem moure virtualment. Ens podem sentir a prop de gent que estimem però que viu a centenars de quilòmetres. Els podem veure i parlar-hi en temps real. Podem saber el que ells volem que sapiguem del que fan. Els podem fer saber el que vulguem que sàpiguen de nosaltres. Els podem felicitar. Podem fer-los sentir bé. En definitiva, ens podem sentir menys sols, menys estranys, menys aïllats i podem fer que els altres també estiguin més acompanyats. La socialització és també un exercici de solidaritat.

En la meva opinió, no val l’excusa que les TIC ens esclavitzen. Ho poden fer si deixem que ho facin. Però si la nostre capacitat de tria preval per sobre de tot, com ha de ser, ens fa més propers, més ben informats i per tant, millors. Companys de generació, doneu el primer pas i entreu a les xarxes socials. Potser vareu perdre el tren directe, però encara us queden els rodalies. Passen per la vostre estació cada dia. Potser amb el retard habitual de Renfe, però això juga al vostre favor.

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Heliogravure V – About Etching

Cu_29_65_Gris_96In photogravure on copperplate, etching  is commonly done by immersing the plate in several solutions of ferric chloride of different concentration. As the pigmented gelatin is thicker where the image tone is higher, the trick is to allow the ferric chloride to penetrate before the thin gelatin in the shadows areas  and progressively do the same up to the highlights. It is usual to put a grey scale step wedge aside the image on the same plate. This serves to control the etching progress. General advise is to change the plate to a more diluted ferric chloride solution when it is not more apparent etching. In an ideal situation, the plate will show equal etched steps for more or less equal periods of time. This supposes that the copper etching is constant once the ferric chloride had passed through the corresponding gelatin thickness. For a given carbon tissue, there is also a recommended group of ferric chloride dilutions that will perform a correct etching.

But, what is a correct etching? If the goal is to achieve a complete tone scale, as usually is, the answer implies that what we want to complete is an etching deep inversely proportional to the tone in the image. The low (darker) the tone, the more deep the etching. This ensures a high charge of ink for the shadows and smaller quantities for the highlights. Additionally, a correct etching should provide the darkest and deeper black avoiding open bite caused by lateral etching. This determines a maximum total etching time. It must be previously determined using the same screen that will be used with the actual images. Once the maximum etching time is found, there is also necessary to find which is the first dilution of ferric chloride concentration capable to penetrate the shadows in a reasonable time (usually 2min) and the last dilution that preserves the white highlights. The departures of those indications would be corrected changing the positive density scale and/or the respective screen and positive exposure times. Following the instruction sheet of the Dragon Gravure tissue from Cape Fear Press, this would be accomplished by a sequence from 45ºBé to 40ºBé.

In practice and even following all above recommendations, the results are not always the expected. Even with a deep and rich black without open bite and a clean and brilliant white, the final aspect of the print can show a certain departure from the original image. It is common that, even with those correct ends of tonal scale, the relationship between the steps of the medium grey values is different of those of the step wedge. Another common problem is that following the etching progression by visual inspection, it is difficult to observe the previously determined total etching time without risk of over etching the highlights. Attending to those difficulties and looking for a better controlled etching procedure, there are some questions that must taken into account.

From a text published by H. M. Cartwright in 1961 (1), it can be derived that the etching action of the ferric chloride is highly dependent of its concentration. This indicates that the concentration not only determines its ability to penetrate the gelatin resist, but also acts with a different speed when finally is in contact with the copper. The Fig., 1 shows a plot taken from this text representing the depth achieved by several ferric chloride dilutions on a copper plate for a given time.

Etching_Depth_10_50Be

Figure 1

As can be observed, the etching power of the ferric chloride on copper rises up as a function of the concentration. This occurs up to 33ºBé approximately, from where the activity goes backwards decreasing again. If we take a portion of this plot, that corresponding to the concentrations between 39ºBé and 45ºBé (Fig., 2), we can realize that is almost linear. In addition to its capability of resist penetration using gelatinized paper, this is a good reason for to be a group of dilutions highly recommended in many texts.

Etching_Depth_39_45Be

Figure 2

In spite of this linearity, the figures in the depth units indicate that the activity of a 45ºBé solution is of only the 73% than that of 39ºBé. This suggest that if we want to progress a constant depth into the copper along the total etching time, the plate must remain more time in the concentrated solutions and less as it is immersed in those more diluted. Following this hypothesis and for a given total etching time, it can be divided in as many parts as dilutions will be used. The weighted individual time for each is derived in turn from the activity shown in the plot of the Fig., 2.

As an example, we suppose that our total etching time producing a rich black is 25min and the dilution that penetrates the shadows resist is 45ºBé. Following with the example, the last dilution that still avoid an over etching of the white patch in the step wedge is 41ºBé. A weighted etching sequence derived from the upper plot is shown in the Table 1.

Table1_EtchingSequence

Table 1

There are still two more questions that might be taken into account. The first, related with the influence of the temperature in the etching progression. The second, the swelling of the resist and the following ferric chloride penetration. The influence of temperature can be derived from a graph in the same Cartwright (1) text cited above (Fig., 3). The paragraph says textually that “There is a practically straight-line relationship between temperature and the rate of etching, at least within the ordinary working range… Depth increases about 2% per ºF rise” (≈0.66% per ºC).

Etching_Temp

Figure 3

The same text explains that although a higher temperature improves the uniformity of results, around 90ºF (32ºC), the ferric chloride tends to weaken the resist. In my own experience, this occurs before, around 26 – 27ºC. Probably the strength of the resist is different as a function of a given carbon tissue and the hardening degree, that depends mainly from the wavelength of the UV light source output. If the resist weakens, the highlights are quickly over-etched. In any case, maintaining the ferric chloride solutions temperature as a constant, say to 21ºC, is very important in order to control the etching sequence and how it affects to the tone scale. If this is not possible, the actual temperature should be read and the general scheme correspondingly modified. The total penetration depth achieved, is responsible for the correct black density and, if exceeded, risks the apparition of open bite.

Conversely to this linear behaviour, when the plate is immersed in the ferric chloride baths the swelling of the resist is not linear at all. Justifying the need of more than one ferric chloride bath, the same Cartwright explains in a text of 1930 (2): “It is assumed that, when a solution of a salt such as ferric chloride is applied, two separable processes take place. The first of these is the swelling of the gelatine, which goes to a maximum and then the diffusion of the ferric chloride solution begins. The maximum swelling is not proportional to the time, but is rapid at first and then slows down as the maximum is approached”.

If all those interlaced relationships between the resist hardness, the resist swelling, the ferric chloride penetration and the etching depth on copper were linear in response, it would be possible to etch a plate with a unique solution of ferric chloride. It is important do not forget that the goal, beyond a rich black and a clean white, is a linear grey scale in between. May be because my reduced experience, I have found that this necessary linearity is hardly achieved only by visual inspection over an step wedge. Scanning the printed results for an step wedge, shows that the visual inspection drives each time to a different results with only a common characteristic, the lack for a linear response. Wondering about that, it seems to me that a simplified method would be more effective if the above given non-linearities are come into play. Since a video of Fanny Boucher (3) and after an email dialogue with Jon Goodman (4), I have noticed that both are using only two ferric chloride solutions. Then, I have decided to try with this procedure.

The sequence of steps for testing the suggested etching method is as follows:

  • Exposing a tissue sequentially to the digital screen and then to a black transparency printed with the usual settings in the inkjet printer, is useful to determine the minimum exposure times that produces as thin as possible resist layer. The thickness of the resist is better seen transferring the gelatine on a transparent glass with the same method used with copperplates (5). A transmission densitometer reading or a digital image reproduction both with camera or scanner, can help to distinguish this thin resist layer from the glass background.
  • Once this minimum exposure times are determined, what is necessary now is to find out which is the etching time that produces a rich black without open bite risk. This is done preserving strips of the copperplate with packaging tape during the etching with a very diluted ferric chloride solution, that is to say, 39 – 40ºBé.
  • Take, for instance, four correctly exposed tissues using the digital screen and a step wedge printed with the same method that will be used with actual images and transfer them on an equal number of copperplates.
  • Prepare four ferric chloride baths of decreasing concentration. That is to say, for example, 45º – 44º – 43º and 42ºBé.
  • Following with the previous example, consider four couples of baths, (45º – 44ºBé), (44º – 43ºBé), (43º – 42ºBé) and (42º – 41ºBé). Taking the total etching time previously determined and the values shown in the Fig., 2, it is possible to calculate how many time the plate must be etched in each bath for each couple of baths.
  • Etch the four plates following this schemes and print it with the usual inking, wiping, paper and press.
  • Scan on and measure the grey value of the step wedge patches. Plot a graph that shows the tonal range progression. The goal is an as straight as possible line.
  • Take the best result in terms of linearity and fine tune the grey scale applying a Correction Curve to the test target image in Adobe Photoshop or any other digital image processing software.

The Fig., 4 shows the linearity of grey tone scale achieved (in red) after to apply a Photoshop correction curve to the best result in the previous assay (in blue).

Helio_46_Plot_BeforeAfter

Figure 4

The Photoshop correction curve follows from the actual reading values for each step in the printed target. In order to calculate the necessary correction, we can use an spread sheet and create a column with the actual read values in a column (J in Fig., 5) and then use an equation to calculate the corresponding target values (column K in Fig., 5). If we take the example of the calculated target value 220, it is the result to apply the equation =K3-((J$3-J$13)/10) in the cell of the spreadsheet. The procedure to plot the correcting curve can be done in Adobe Photoshop setting the actual and target values in the correspondingly input and output windows of the Curves Tool. This correction curve can be saved with the available commands in Adobe Photoshop and then, applied to all images to be printed as positive transparencies.

Actual_Target_Corrected_Values

Figure 5

From the comparison between the two plots in the Fig., 4 it can be derived that although both show correct shadows and lights endings, the progression of the intermediate grey scale is linear only in the graph obtained from the corrected positive transparency of the test target. In this way, we can not only simplify the etching step, but also preserve the image visual appearance as we have edited it in the computer screen. A bit closer to a WYSIWYG system.

REFERENCES

  1. CARTWRIGHT, H. M. (1961) ILFORD GRAPHIC ARTS MANUAL Volume 1 Photoengraving. Ed. Ilford Limited, Ilford, Essex.
  2. CARTWRIGHT, H. M. (1939) PHOTOGRAVURE A Text Book on the Machine and Hand Printed Processes. Ed. American Photographic Publishing Co., Boston.
  3. FANNY BOUCHER Héliograveur (2013) Réalisation d’une Héliogravure du photographe Georges Saillard. On line https://www.youtube.com/watch?v=FsRZcEVCXAI. Last visit: July 12th 2016.
  4. GOODMAN, Jon. Jon Goodman * Photogravure. On line: http://jgoodgravure.com/index.html. Last visit: July 12th 2016.
  5. MORRISH, David & MacCALLUM, Marlene (2013) Copper Plate Photogravure, Demystifying the Process. Ed. Focal Press, New York/London.

 

Posted in Early Photography, Heliogravure (english / français) | Tagged , , , , , | 1 Comment

De la Visualización a la Imagen Final

Planteamiento Inicial. Ante una determinada escena o situación, el fotógrafo puede tomar al menos dos caminos. El primero y más común es el de documentar la escena y los sujetos que la componen. Aunque esta opción no está privada de una cierta dosis de creatividad, la documentación impone reglas y limita las opciones frente al contenido de la escena y sus características. Una segunda opción frente a una misma escena, es la de utilizarla como punto de partida para una recreación que, en algunos casos, podría incluso comprometer la comprensión del contenido original. En este caso, la imagen resultante no pretende informar de como era la escena, sino mostrar la idea que provoca en el autor de la imagen, mostrar una idea desvinculada del contenido formal tomando sus elementos como sujetos de una nueva escena o simplemente dar prioridad a una determinada reacción en los futuros observadores.

El planteamiento de la segunda opción descrita en el parágrafo anterior ha sido ampliamente utilizado por numerosos fotógrafos a través de la historia de la Fotografía. En este contexto, la metodología de trabajo de cada fotógrafo condiciona y contribuye a su vez la imagen resultante. Un sistema descrito por Ansel Adams y posteriormente discutido y ampliado o modificado por otros autores, es el de la llamada Visualización. La visualización consiste en intentar imaginar qué se desea tener en la imagen final antes que esperar a ver qué es lo que registra la cámara para luego decidir si cumple o no con nuestras expectativas. Este proceso incluye mecanismos de reflexión, de índole psicológica y en algunos casos, planteamientos filosóficos. A grandes rasgos, el sistema implica tres etapas principales:

  • Intentar descubrir cuál o cuáles son los mecanismos que nos han inducido a desear captar la imagen. Esta etapa es puramente reflexiva y podría realizarse al margen de si posteriormente se registra o no la imagen.
  • Establecimiento de las condiciones técnicas que ayuden a la captación de la imagen teniendo siempre presente los condicionantes que impone nuestra visualización de lo que queremos ver en la imagen final.
  • Procesado o pos-producción de la imagen como una continuación del proceso de captación/creación de la imagen.

Resulta interesante constatar que las tres etapas, aunque fueron descritas en las primeras décadas del Siglo XX, son perfectamente adaptables a la utilización de los actuales instrumentos y procedimientos fotográficos, sean éstos foto-químicos o de soporte electrónico.

Caso de Estudio. En las primeras lazadas de la pista forestal que parte del Plan de Senarta, en el Valle de Benasque, y remonta el Valle de Vallibierna hasta la Cabaña de Coronas, la pendiente atraviesa un bosque espeso en la vertiente umbría del valle compuesto principalmente de coníferas y algunos ejemplares de haya, aliso y abedul, además de los arbustos propios de este tipo de bosque. En una ligera curva a la izquierda, el bosque muestra un pequeño claro en el talud por encima de la pista y a la derecha según se asciende. En la parte superior de este claro hay un aliso solitario que, desde el punto de vista de la pista, presenta unas raíces descarnadas y completamente por encima del nivel del terreno.

En Noviembre de 2014, paré el coche en el margen de la pista, atravesé el linde del claro y remonté la pendiente hasta una cierta distancia del árbol desde la que me pareció interesante la relación entre la figura y el fondo. Posicioné el trípode a media altura para un encuadre en formato cuadrado aprovechando la parte superior de un fotograma vertical. La idea era resaltar los esfuerzos del árbol por deshacerse de su atadura al terreno. Ésa era mi propuesta y a esa distancia, el objetivo más adecuado entre los disponibles era el 55mm. La imagen obtenida es la que se muestra en la Fig., 1; en la misma figura se aprecia el recorte cuadrado en la parte superior del fotograma.

Sceen_Cropping_Nov2014

Figura 1. Recorte del encuadre original de la imagen tomada en Noviembre de 2014, en la interfaz gráfica de usuario de Adobe Photoshop (click en la imagen para ver una versión ampliada).

Una vez editada la imagen, la conclusión fue que no cumplía con las expectativas generadas en el Valle de Vallibierna. Aunque la idea general es correcta, algo limitaba la idea de ascensión hacia arriba, esencial en la visualización inicial.

En Abril de 2015, cinco meses después, una nueva visita al Valle de Vallibierna me permitió volver al claro del bosque con el aliso solitario. Teniendo en mente la imagen tomada en Noviembre, esta vez remonté la pendiente hasta el mismo nivel del árbol. Después de algunas indecisiones, el trípode se posicionó de forma que permitiera un punto de vista algo elevado por encima del conjunto de raíces. La cercanía de la cámara al árbol aconsejó en este caso la longitud focal de 35mm. El encuadre era esta vez algo más amplio pensando en al posibilidad de re-encuadrar a voluntad sin llegar al plano cerrado de la imagen de Noviembre. La imagen captada y el recorte aplicado se muestran en la Fig., 2.

Sceen_Cropping_Apr2015

Figura 2. Recorte del encuadre original de la imagen tomada en Abril de 2015, en la interfaz gráfica de usuario de Adobe Photoshop (click en la imagen para ver una versión ampliada).

En este caso, la relación del árbol con el entorno resulta interesante pero sigue sin mostrar, en mi opinión, la idea gestada en la visualización. Aún así y en una revisión positivista de la imagen, la distribución de las ramas que emergen del tronco en relación al fondo y entre sí mismas, es algo menos estática que en la versión de Noviembre de 2014.

Al cabo de un año, en Abril de 2016, una tercera visita al valle empieza por un paseo por el claro del bosque sin intención previa de emplazar la cámara en ningún lugar concreto. Ya de vuelta al coche, al pie de la pendiente, vuelvo a experimentar la misma percepción que la primera vez, un año y medio antes. En realidad, si esa percepción de árbol en ascensión se dio en esta posición, quizá es desde este emplazamiento desde el que debería tomarse la imagen. Vuelvo al inicio de la pendiente tras los árboles del margen de la pista, monto el trípode y la mayor distancia al árbol me obliga a utilizar el 135mm para encuadrar un entorno parecido. Esta vez tengo también en cuenta un ligero desplazamiento a la izquierda con respecto a la primera toma para controlar la relación de las tres ramas con el tronco y entre sí mismas. Con este punto de vista más alejado, el tronco delgado del fondo toma ahora más protagonismo y debe controlarse su obstrucción visual con el tronco del aliso. La imagen captada y su recorte se muestran en la Fig., 3.

Sceen_Cropping_Apr2016

Figura 3. Recorte del encuadre original de la imagen tomada en Abril de 2016, en la interfaz gráfica de usuario de Adobe Photoshop (click en la imagen para ver una versión ampliada).

En esta ocasión, la porción recta del tronco ocupa dos tercios del encuadre, ganando en presencia. Por su parte, las ramas resultan más aéreas. El punto de vista más bajo y el encuadre algo más abierto muestran con más claridad la pendiente del claro del bosque hacia la derecha. Todo ello unido a la dirección marcada por la reunión de las raíces en la base del tronco, refuerza la idea de esfuerzo de ascensión. En cualquier caso, el conjunto es más acorde con la idea inicial. En la Fig., 4 se muestran las tres opciones.

Sceen_Cropping_Squared_x3

Figura 4. Las tres tomas citadas en el texto a efectos de comparación (click en la imagen para ver una versión ampliada).

Al margen de lo que cada cual pueda considerar en relación a la mayor o menor coincidencia con los criterios explicados para dar las respectivas imágenes por buenas o no, queda patente en este caso que el mecanismo perceptivo que desencadenó la intención y necesidad de captar la imagen se inició en un lugar preciso al pie de la pendiente del claro del bosque. Cualquier otro punto de vista conduce a imágenes probablemente válidas en otro contexto, pero que no cumplen con la expectativa que uno mismo se había creado acerca de la imagen final. Es seguro que tantos fotógrafos como lean este texto pueden tener su propia opinión sobre lo que se ha narrado y es más que probable que si un día visitan el Valle de Vallibierna acaben por hacer una toma completamente distinta de este mismo árbol. Probablemente ésta es una de la bondades de la Fotografía, que nos proporciona tantas visiones como individuos la practican.

Finalmente, en al Fig., 5 se muestra la imagen final después del procesado que en este caso, se ha realizado en blanco y negro. Pero ésa es otra historia…

AlienTree_Final

Figura 5. Edición final de la imagen comentada en el texto (click en la imagen para ver una versión ampliada).

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Digitization System for Film Negatives and Slides (II)

Sistema_Repro_NegThe last post, Digitization System for Film Negatives and Slides (I), was dedicated to comment the oportunity to use a former photographic enlarger head as a part of a film digitization system by means of a digital camera. This second post comments aspects related with the illumination eveness in the diffusser supporting the negatives or slides to be reproduced.

In first place it is necessary to check the lighting uniformity taking an image from the diffuser deliberately defocused. This defocusing helps to avoid material irregularities and possible dust particles on the diffuser surface. Plastic materials tend to charge static electricity and attract any kind of small particles. Defocusing the diffuser is also achieved the manner of its normal function when the focus is adjusted over the negative or slide surface. Provided that the originals to reproduce are completely flat, depth of field is not necessary and then the diaphragm aperture can be adjusted in order to avoid any problem with diffraction. This image must be taken with the camera, lens and aperture that will be used in the film digitization. It must also be taken into account the working distance for the film size. In the examples that follow, the camera and lens used corresponds with those described in the former post. The working lens aperture is f/11 and de negative carrier framed is of 4×5” (10×12.5cm).

Once the diffuser image is available, it must be saved as a TIFF image format without compression in order to avoid changes in the pixel gray values. Next step is to take measurements of pixel brightness of at least three directions: Vertical axis, horizontal axis and diagonal axis. This can be done using several digital image processing software as ImageJ, NIHImage or Fiji. The Fig., 1 shows pixel gray value plots for those three axis in the case of the example.

Plot_Diffusser_VHD

Figure 1. Pixel gray value plots taken, from left to right, over the respective vertical, horizontal and diagonal axis of the diffuser image (click on the image to view an enlarged version).

As can be observed, the illumination uniformity is near perfect with the system described. The differences between centre and corners are of less than ten gray values in the scale from 0 to 255 for the diagonal axis measurement. In the Fig., 2, a three dimensional graph of the whole image gray values, can be easily observed this little difference between. For the majority of applications, this little difference is absolutely negligible and hard to be detected by the naked eye, specially with pictorial images. In this case, the enlarger diffuser and the optical vignetting of the lens employed, match a high degree of performance for a correct reproduction. This series of assessment must be performed for all different taking distances suitable to frame the different film formats.

SurfacePlot_Diffusser

Figure 2. Three dimensional graph of the pixel gray values taken from the diffuser image (click on the image to view an enlarged version).

For those situations where the reproduction exigences a perfect degree of uniformity, that follows is a series of digital image processing that can be performed in order to compensate those little detected differences. The procedure allows to work in the defocused diffuser image into a software like Adobe Photoshop. The goal is to generate a Curves Adjustment Layer compensating those differences in luminosity.

The steps are as follow:

  • First step is to take Color Samples in the center and the four corners of the image. Photoshop shows the results of the color samples in the Info Palette.
  • Create a Curves Adjustment Layer on top of the Background Layer containing the defocused diffuser image.
  • Copy to the System Clipboard the image on the Background Layer.
  • Paste the previous copied image into the Curves Adjustment Layer Mask.
  • Having selected this Layer Mask, invert the image values (Image>Adjustements>Invert).
  • Selecting and viewing in the screen this Layer Mask (Option or Alt key + Click on the Layer Mask), apply a histogram expansion by means of the tool Levels or Curves. On both cases, the triangle sliders at left and right must be moved to the extremes of the histogram. Using the Levels tool, it is very important do not change manually the position of the gray triangle slider that indicates the middle value of the scale. In the case of the Curves tool, do not apply any change in shape other than the right line, now with a higher slope.
  • Then, with the Layer Mask adjusted as previously described, modify the curve rising the brightness without any change in contrast. This is done modifying the Input and Output values of both Black and White in a such manner that the final shape is right and parallel to the previous default line. The values to apply will depend on the differences detected in the previous measurements.
  • In any case, the effect caused by successive adjustments can be monitored by the indications in the Info Palette. Photoshop, being an active Adjustment Layer, indicates the gray value of the five color samples followed by the value they will take applying the corresponding adjustment. Each couple of values is separated by a slanted bar. The final “curve” shape must be a right line and parallel to the initial default right line.

Remember that we are applying a uniform rising of luminosity that in turn is controlled by the contents of the Layer Mask. This mask contains all the image irregularities normalized to the scale from 0 to 255 and with its values inverted. The more dark the pixels in the mask, the lower the adjustment is applied to the image. Conversely, the lighter pixels in the mask represent the pixels of the image that will be modified. The adjustment will be complete in the areas where the mask pixels are plain white. The Fig., 3 shows the graphic interface from Adobe Photoshop with the curve applied in the example.

Screen_CompensatingCurve1

Figure 3. Adobe Photoshop user interface showing the color samples and the Curve Adjustment Layer applied as is explained in the text (click on the image to view an enlarged version).

In the Info Palette shown at the Fig., 4 can be observed the gray values of the color samples before and after the curve adjustment. The example shows as after the curve adjustment, the values are the same for the center and the four corners of the image.

Screen_ColorSamples1

Figure 4. Adobe Photoshop user interface showing the color samples in the Info Palette (click on the image to view an enlarged version).

Nevertheless, the initial value in the center has raised four gray values into the scale from 0 to 255. Now we can follow fine tuning the curve adjustment or, even more simple, apply a second adjustment curve that diminishes those four gray values. Fig., 5 and 6 show this last correction.

Screen_CompensatingCurve2

Figure 5. Adobe Photoshop user interface showing second Curve Adjustment Layer applied as is explained in the text (click on the image to view an enlarged version).

Screen_ColorSamples2

Figure 6. Adobe Photoshop user interface showing the color samples after the fine tuned adjustment (click on the image to view an enlarged version).

These curves can be saved as custom pre-sets and then be applied on all the captures performed with the same working conditions. It can be also generated a Photoshop Action to be automaticly applied to a series of images laying in the same directory. Finally, the Fig., 7 and 8 show gray value plots similar to those previously shown (Fig., 1 and 2), after the smoothing of the illumination irregularities. All this plots confirm the efficiency of the proposed method.

Plot_Diffusser_Flattened_VHD

Figure 7. Pixel gray value plots taken, from left to right, over the respective vertical, horizontal and diagonal axis of the diffuser image after correct the illumination unevenness (click on the image to view an enlarged version).

SurfacePlot_Diffusser_Flattened

Figure 8. Three dimensional graph of the pixel gray values taken from the diffuser image after the correction of illumination unevenness (click on the image to view an enlarged version).

Posted in Early Photography, Heliogravure (english / français), Photography, Photography Technique | Tagged , , , , , , , , | Leave a comment