SINAR Information No 25

From Exposure to the Printed Reproduction

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Better results based on awareness of the problems and up-to-date techniques

By Gerhard Muhlebach, photolithographer (Bergdietikon, Switzerland), and Hans-Carl Koch, M.Sc. mech. eng. ETH (SINAR AG Schaffhausen)

You have surely had clients disap­pointed with printed leaflets or brochures for which you have taken pictures. Usually, you get much of the blame, too. Yet, with today’s know-how this should not happen. You should know what can go wrong at the start, when you take the pictures. You ought to know also how a photograph is related to a printed reproduction. For a photographic print and printed paper are two quite differ­ent media.
Good results in print depend on careful planning when you shoot the pictures to be reproduced. You must know what you want in print and the factors involved. Photographers tend to forget that print processes differ in charac­teristics, paper, screen rulings, ink weight etc. You must allow for the fixed conditions specific to the process – hence the original must suit the medium in which it is to be printed. We shall deal here with the main ways in which printing af­fects image quality and with how to achieve the best results.

The process sequence

Economics and technicalities of printed reproduction – from the first approach to the end product – closely link the skills involved in it. The job of the professional photographer is to produce a best possible record of the original subject. That largely determines the reproduction quality – for the reproduction can be no better than the original. The process operator has to convert photo­graphic copy to printed images – allowing for printing criteria as much as for clients’ preferences. Again the printing run can be no better than the reproduction qual­ity preceding it. The process se­quence involves compromises of tone and colour gradation all the way from the original to the printed image.

Photographer, client and process operator often have different ideas of what the original to be reproduced should be like. What counts for the photographer is the creative and pictorial impact. The client is concerned with suitability for his purpose and message. The graphic arts technician looks at process characteristics. These different criteria have to be brought to a common denomina­tor. Failure to appreciate these problems will at the end leave at least one of the parties involved disappointed. So note the condi­tions and limitations from the out­set.

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Technical scope and limitations

Current process equipment is highly sophisticated. To match the printing medium, modern scan­ners can extensively control coul­our rendering, highlight and shad­ow gradation and density range of an original. But the most ad­vanced techniques cannot add to an image what was lacking in the
photographic original. There is no way of remed in that originals
shortcomings.
The main technicalities involved concern:

Detail resolution and halftone screen ruling
Current printing processes break up an original image i􀀈to halft?ne dots. This affects detail resolution.
Printing on poor paper, for in­stance newsprint, needs a very coarse screen. This loses fine de­tail – you have to allow for that when taking the picture.

Image contrast and contrast compression
The density range ( contrast) of a transparency is usually greater than can be reproduced in print. When you produce a colour trans­parency, this shows a contrast greater by a factor y of about 1.7 than the brightness range meas­ured in the camera’s image plane. Hence a print of a colour transparency invariably involves a compro­mise. The contrast range of black­and-white originals – and gen­erally of negative materials – is smaller and therefore easier to handle. Hence the printed result is necessarily inferior to the original transparency in brilliance and colour saturation. That’s when the client starts complaining of weak printing or washed-out colours. Process reproduction therefore involves compromises to adapt the contrast of a photographic original to the tone range repro­ducible in print. Despite numer­ous technical aids, compression curves for such adaption are still established by rule of thumb. Even with a matching tone range in the image a snow scene, a landscape with thundery sky and a fashion shot need different reproduction curves to make the printed result look satisfactory. The greater the tone range of the original, the more difficult the compromise be­comes. The photographer can help by correct technique – know­ing why and how to keep the tone range of a scene under control, and how to select a suitable com­pression curve.

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Photographic requirements and recommendations

Can practical picture taking allow for such technicalities? Analysis of potentialities and limitations of related techniques has shown that many of the requirements can in­deed be met – though occasion­ally with compromises. But as long as you know how the pic­tures are to be used already when they are commissioned, you can plan to make them ideal for their purpose. So the assignment should define:

• the point of the pictorial mes­sage (including layout instruc­tions) and
• technical process conditions (paper, screen ruling, general quality requirements).

By matching your approach and technique to these points you make your real contribution to the whole job – from exposure to the final printing. Equally, however brilliant and creative your picture may be, if it won’t reproduce well, your client won’t be happy with it – nor with you as a photographer.

Detail resolution and sharpness
Where the image needs sharpness, the picture must be absolutely sharp. So look after adequate large detail (resolution) for the intended reproduction.
In particular:

• Match the size of detail and ex­panses of tone to the screen and paper on which the picture will be printed.
• A transparency will never be sharper than you focus it on the ground glass screen. So accu­rate focusing is vital. (Select a plane of maximum sharpness by two-point focusing and by the Scheimpflug rule. Stop down only just far enough for the depth of field you need. Use good viewing aids to judge the screen image exactly – you can­not afford to sacrifice overall definition.)

Correct colour rendering
Colour pictures should faithfully render the original colours, with­out lighting casts and without film processing faults.
In particular:

• Note that the colour of the light greatly affects the subject ren­dering. Thanks to adaptation, our eyes tend to ignore unusual colour effects in familiar ob­jects. So use tungsten or day­light type film to match the sub­ject lighting. Excessive blue skylight affects all colours. Thus blue sky degrades the colour of brown skin – which gets further emphasised in the reproduc­tion. Such cases need appropri­ate filtering or fill-in flash.
• To avoid irremediable colour shifts, allow for reciprocity fail­ure with long exposure times and use the conversion filters recommended by the film man­ufacturer. The most elegant way of doing this is to use spot read­ings in the film plane (which au­tomatically allow for conversion filters) and the SINAR Digital shutter (for precise exposure timing) with a module that auto­matically compensates for reci­procity failure characteristics of different films. Where faithful colour is vital, you need precise technical aids with long expo­sure times.

Undamaged photographic originals
The photographic original must be free from mechanical damage such as kinks, scratches, stains etc.
In particular:

• Take great care in handling pho­tographs. Flaws show up less in a large-size transparency than in a medium-format or 35 mm one. Preferably mark detailed reproduction instructions clearly on a transparent overlay to avoid damaging the transpar­ency itself.

Controlled brightness range
The photographic original should show good highlight and shadow detail. The density range between the brightest highlight (short of catchlights) and the darkest shad­ow detail should not exceed 2.55. In a transparency (of gamma 1.7) this is a maximum brightness range of 5 EV when measured in the camera’s image plane (con­trast 1: 32 or density range 1.5). The exposure must be correct within ± 1/3 EV, otherwise you can­not rely on adequate highlight and shadow detail. Easier for subse­quent reproduction is a bright­ness range in the image plane of not more than 4 EV ( 1 : 16 or den­sity range 1.2) which yields a den­sity difference of 2.05 between brightest and darkest tones in the colour transparency. For shooting this also has the advantage of greater exposure latitude.
In particular:

• Note the values established during shooting and mark them on a transparent overlay placed over the finished transparency.(Mark the brightest highlight, deepest shadow, midtone and data of important colour areas, points to be emphasised, mood etc.)

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What you should pass to the pro­cess department is the transpar­ency with these data. Then there is no room for misunderstandings. If the brightness range as meas­ured in an image plane does not exceed 4, or at the most 5 EV and the data are marked as recom­mended, you can be sure of simi­lar optimum reproduction in print. Depending on the subject and exposure conditions reduce the brightness range by one or more of the following measures:

• Adjust the lighting. (Filling in shadows is easier than reduc­ing the lighting level of brightest subject areas.)
• Change the viewpoint. (Differ­ent viewpoints may involve dif­ferent levels of light reflected from the subject.)
• Rearrange objects in the scene. (This could hide deep shadows or eliminate catchlights and flare.)
• Surface treatment of selected objects. (Painting in a different colour, use of matt sprays and other handiwork on the sub­ject.)
• Use polarising filters to cut out reflections.
• Use graduated filters or colour filters to hold back certain sub­ject tones.
• Add fill-in lighting with white re­flectors around the subject, or deliberately generate stray light within the camera body with white paper inserted in the bel­lows.

Any one of these measures may fail or even make matters worse if you do not carefully measure the effect by spot exposure readings in the image plane.

Correct exposure metering

All meter readings should be spot readings in the film plane with all light excluded from the rear of the screen. That is the only way of pre­cisely allowing for camera exten­sion, aperture tolerances, lens transmission, stray light in the camera, filter factors etc. The im­age plane of a view camera is big enough to permit full selective lo­cation and readings of a measur­ing probe. Suitable equipment is available from SINAR and can be used in manual mode with all view cameras. The automatic DIGITAL shutter system with the SINARSIX digital and module can equip all SINAR view cameras for up-to­date automatic processing of me­ter readings and exact exposure settings. Important is also that the metering system operates equally for continuous light, flash and even mixed lighting.

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Summing up

Over the years an experienced professional usually acquires some knowledge of the reproduc­tion sequence from exposure to the printed result. Accurate meter readings and specification of the original may even seem an un­necessary bother. But such ex­tensive experience is only of limited use with unusual assign­ments. The most experienced hu­man eye still cannot reliably esti­mate subject brightness range -the eye’s adaptation compen­sates brightness differences. On the other hand, modern metering techniques combined with microelectronics get you there much faster and more precisely – with any lighting setup and sub­ject – for best possible photogra­phy.
Of course you may have to com­promise even if you follow the ways suggested here for solving problems. But such compromises will be more effective if you know what is involved.

Once you realise that the tone range of the printed page is far smaller than of any colour trans­parency, you can make your dra­matic point in other ways and still preserve good reproduction. For instance you can rely on pictorial contrast – light against dark, bril­liant against pastel hues, rounded and square shapes, large and small objects, calm and live moods or coarse against smooth texture.

It is rarely enough to admire the beauty of a picture. You have to ask yourself whether the original is indeed suitable for a given print­ing medium. If the latter cannot satisfactorily reproduce the pic­ture, it is pointless to try and see whether the result is usable. Creative photography is important – but so is precise measurement to keep tone values under the control needed for correct photo­mechanical reproduction. Only then can the photographer’s ef­fort get across in print. That can enhance photography – at a time when technology tends to swamp other crafts. It is also the best rea­son for the photographer to be­come thoroughly familiar with what he can achieve.