Photographic printing

Ausbelichtung is a gridless method for fixation of analog image data. As templates are films ( negative or positive) or files.

• 4.1 film on photo paper
• 4.2 File on photo paper
• 4.3 Other factors influencing
• 4.4 Analog output material
• 4.5 Digital output material
• 4.6 differentiation

Basic principle

Ausbelichtung done in most cases on photo paper (not to be confused with printer paper, which is usually called "photo paper" and is printed by a grid method ).

Principle, however, other similar materials are possible:

• Negative or slide film ( from a file is created, a conventional negative or slide )
• Printing film (all colors to be printed - usually four - will image each on a movie and needed in another printing process as a template )
• Archive film ( a file is usually contrasted exposed on a film with special format )

The need for prints on photographic paper is growing annually. The proportion of includes prints on other materials is constantly falling.

Includes prints are always grid-free, since the image pixels are not rasterized and because " merge " by various physical causes of exposure, the individual pixels of each other. In ( rare and ) the worst case, this can lead to a decrease in the sharpness impression.

Following two methods will be described an example here:

Film on photo paper

Light is sent through a film that the underlying photo paper is exposed to proper type (brightness, sharpness, ... ). After exposure, the photo paper on a conventional ( chemical ) type is developed. This method is grid-free.

• The brightness of the incident on the photographic paper is controlled by the duration of the exposure.
• The color mixing is controlled by the use of color filters which are located in the light channel between the film and print paper.
• The sharpness is regulated via an objective

In Ausbelichtern that offer image optimization, is located in the waist yet a transparent special disc. This transparent plate can be partially blackened by electricity. Thus, the most important optimization techniques can ( change in contrast, unsharp masking Burn, Dodge ) are carried out in a split second.

File on photo paper

Each pixel is converted to a particular light pulse. Controlled there is hue and brightness. Thus, the photo paper is exposed. After exposure, the photo paper on a conventional ( chemical ) type is developed. For use come tubular exposure, laser imagesetter or platesetter LCD. This method is grid-free.

Approx. 90 % of auszubelichtenden data are from amateur photographers. To compensate for the poor quality of these data, through all the pictures an automatic optimization process ( change in contrast, unsharp mask, ...). This optimization can be reduced, but not prevented.

Aspect ratio

In addition to the classic photo formats ( aspect ratio of 1:1.5 mm film ) there are countless special formats. Most unusual formats created by digital photography and are protected by the design of the sensors (frequent aspect ratio of 4:3) or the post- conditioned.

Usually rolled photographic paper is used. The closing date follows the aspect ratio provided by the file (usually but ) maximum to the classical aspect ratio of 1:1.5. After development of the photographic paper that is cut. Here, each photo will be cut according to its individual length.

A problem for most Photosensitive provide panoramic formats dar. While it is exposed on roll paper, but the outer edge of the light emitter is - structurally related - mostly made in an aspect ratio of 1:1.5. Principle, however, is not a problem also the panoramic scene at the closing date

If no request made ​​cutouts, images compressed or can not connect panorama formats are fully exposed, this has economic reasons. To create a photo as cheap as possible, is completely without individuality. The European market is in this case dominated by one supplier ( CeWe Color), which supplies almost all the filing offices ( drug stores, gas stations, center, electric markets, ...). Alternative Ausbelichtungsmöglichkeiten are only to be found in niche areas.

The currently largest Ausbelichtungsformat in the amateur field is 76 × 300 cm.

Template size

The size of a template ( see also image resolution ) is one of several factors that affect significantly the quality impression playback.

The majority of prints on photographic paper are made as an amateur work. The values ​​given in the table for the original size are approximate values ​​, to use the full print resolution can.

In the professional area is higher, often exposed but also with similar image sizes. The biggest difference in quality make the Profiausbelichtungen of the better contrast differentiation.

The second major difference between amateur and Profiausbelichtungen is in the image optimization.

• In the amateur one goes from the manufacturing process of data low and medium quality - the optimization is correspondingly high. Typical of this is to increase the contrast and sharpness correction ( unsharp masking ).
• In the professional area is assumed that high-quality data. According to lower the image optimization. Since in this type of production is typical for amateur work missing contrast enhancement, Professional includes prints appear at first glance often " flat". This low contrast is but only prevent loss of sharpness.

The resolutions of the Ausbelichtungs units are different; for photo paper machines from 150 to 400 ppi are used. This is dependent mostly economic reasons. An example: If a 50 cm × 75 cm photo with 400 ppi will image, a raster graphic size of about 270 megabytes would be required. Larger data packets result in longer computation time which means the increase of a major cost factor. As part of the current development in computer performance takes place here a gradual adjustment process. As a comparison: Daily newspapers are usually produced with a print resolution of 150 ppi, while the currently best Fotobelichter ( for photo paper) achieve a resolution of 400 ppi.

The resolutions of the Fotobelichter are often adjusted depending on the format: Smaller images are exposed, for example, with 300 ppi, larger with 200 ppi. For includes prints on other materials often much higher resolutions are used. Note: The unit " ppi " should not be confused with "dpi". While this is the actual photo in pixels " ppi ", are meant by "dpi" only the pressure points. In the print preparation several pressure points (typically four printing points per pixel ) is calculated from each pixel. Purely mathematically would a 300 ppi Ausbelichtung equivalent to a 1200 dpi print his ( Qualitatively, the closing date is better, since it is a grid- free method ).

Quality criteria

The main quality criteria of a closing date will be determined by the quality of the original image and the technologies used. The technology consists of the data conversion, image optimization and accuracy of chemical development.

Since the closing date is a grid- free method, the image data without the Interpolationsverlust a printing process can be represented with her. Besides the very high durability (archiving and resistance against environmental influences ) particularly following benefits to come wearing:

Film on photo paper

• In the centuries of the development of photochemical technologies are all parameters that make up a good photo, has been increasingly fine tuned to each other
• Includes prints have advantages over print a larger dynamic range, fine contrast differentiation and clearer colors ( as when printing a portion of the colors are replaced with black )

File on photo paper

• The use of RGB color space for output to film ensures high color fastness, since no color separation is necessary
• Since includes prints are lattice-free method, no additional artifacts ( such as moiré ).
• Includes prints have advantages over print a higher contrast ratio, finer contrast differentiation and clearer colors ( as when printing a portion of the colors is exchanged for Black)

Principle can be of any proposed quality each Ausbelichtungsgröße finished. Technically, there are no restrictions - only subjective quality criteria can here set limits. As an example can here the sharpness are:

The essentials of photos are:

• Soft gradients between colors
• Color areas with natural structuring
• Mergers between various picture elements ( without edges, "like cut with scissors " look ).

The decisive factor for the impression of high definition is therefore:

• The application of the proof (intended use, viewing distance, ambient light, ...)
• The right mix of focus and blur (artistic blur, motion blur, ...)
• The quality of the image optimization (physical sharpness affects only 25% of the impression of sharpness )

All these factors result in no clear threshold above which resolution photo is felt as sharp, but the criteria to optimize the quality of the desired Ausbelichtungsgröße.

Other influencing factors

The same starting material

The sharpness, contrast differentiation and grain size determine the possible image quality for photographic film. These parameters are initially influenced by the film sensitivity. Highly sensitive films have in principle a coarser grain size than films with lower sensitivity. The grain size limits the possible resolution, but a coarser grain size also reduces the diffusion of light within the emulsion, thereby improving the resolution. Furthermore, contrast reproduction and resolution influenced by different chemical and physical effects during development. For example, increase edge effects as the Eberhard effect the contrast at the borders of stronger and weaker points and exposed by the Kostinsky effect, the distance between adjacent exposed points. Such neighbor effects are especially used by fine grain developers for the processing of black and white films to improve image quality.

The common everyday films with a sensitivity of 100 ASA ( DIN = 21 = 100/21 ° ISO) meet all normal requirements in terms of grain size, contrast and sharpness. Includes prints of miniature films up to size 50x75 cm make this is usually not a problem, but there are already significant differences enlargements of 6x7 medium format 50x70cm to see.

Slide film with low sensitivity ( 25 to 50 ASA) offer a resolution of up to 400lp/mm, which corresponds to Kleinbildfilm a digital image of about 40 megapixels. Because in addition to the film properties, the optics of the camera affects quality of limitation, the effective usable resolution is usually far lower.

Digital output material

Important influences on the physical sharpness of digital recording systems have:

• The optical power of the lens: a majority of lenses used in the amateur field are not able to present resolutions above 5 megapixels, especially at wide-open aperture, and in the peripheral areas of the lens.
• The image processing electronics and algorithms: these are differently well suitable approaches for different motives. Also relevant is whether the image data in the RAW format of the sensor or as a composite RGB image already present.
• The noise level: a high-quality look or a low-noise image processing can be at a relatively low resolution to high-order includes prints lead as a poor appearance with verrauschender image processing but high resolution.
• The type of storage: the widely used JPEG format, although economic sense, since it saves disk space; but the camera's RAW format can store as the only complete recording quality.

Differentiation

The displayable colors are, inter alia, by the amount of colors used is determined ( in the camera, there are 3 colors "RGB" ). When printing methods - compared to the closing date - usually more than three colors used. Due to the larger amount of colors creates a different amount of displayable colors. So colors can be represented by many printing processes, which can not supply many cameras, on the other hand be specific - provided by the camera colors not shown by printing processes.

Includes prints use the RGB colors and thus set the camera data with greater similarity is, as it can printing process.

Hybrid method

When Agfa Digiprintverfahren a slide is not fully exposed visually, but first digitized. Subsequently, the closing date is done using a film recorder.

The Agfa Digiprintverfahren was introduced in the 90s in the amateur field, has now become very rare. The low demand nowadays includes prints from the slide is usually with a normal closing date - combined with a special photo paper - settled.