# Digital photography

As digital photography (counterpart to analog photography ) is Photography using a digital still camera or a camera with digital rear wall , respectively.

The technical fundamentals of digital photography differ from classical, optochemically based photography and are similar to video technology on the one hand , and imaging processes on the other , especially when it comes to image conversion .

Non-digital photos ( paper images , negatives , slides ) scanned (digitized) are not referred to as digital photography, but as digital image processing .

## history

The endeavor to store photos electronically without having to make the detour via picture or slide scanners is closely linked to the advent of television in the first third of the 20th century. TV pictures showed that it is possible to transmit pictures electronically and project them directly from the TV camera onto the home device. The big problem, however, was the non-analog storage of these images.

Russell Kirsch from NBS had developed the digital scanner back in 1957 . The very first image scanned in this way was a baby photo of his newborn son Walden, 176 by 176 pixels. Steven Sasson built on these ideas in the early 1970s.

The first camera, which can be regarded as a pioneer of the digital camera , was therefore also referred to as the “ portable all electronic still camera ” and was a prototype developed by Steven Sasson at Kodak in 1975 . The potential of the development was not recognized, however, and so the first commercial camera presented by Sony in 1981 under the name Mavica based on the same functional principle is generally regarded as the “original digital camera”. However, as the name suggests, this camera worked with a magnetic tape (also called a video floppy), which did not allow digital storage of the data. Primarily in the USA, camera manufacturers such as Canon , Nikon , Konica or Fuji brought further developments of this model onto the market. In Europe, interest in this technology was rather subdued.

The first real digital camera was presented by the Californian company Dycam in 1991 at the CeBIT computer trade fair under the name Model 1 . The camera was equipped with a light-sensitive CCD sensor and a memory module that enabled the images to be transferred directly to the computer. Despite the black and white recording mode and a - from today's perspective, low - resolution of 376 × 284 pixels, the trade press was enthusiastic. The US business magazine Fortune even dared the following forecast: “A storm of technological innovations and new products is gathering over the world of photography, which will blow away much of what is well known to this day. Films, chemicals and darkrooms will be replaced by a technology that is dazzling and old-fashioned at the same time: the computer. "

At the photokina , an international trade fair for the photo and image processing industry in Cologne, in 1992 almost all well-known companies from a wide variety of areas presented their prototypes. In addition to classic camera manufacturers such as Kodak and Rollei , the video giant Sony and Leaf were also represented with digital camera studies, because the catchphrase “ digital imaging ” heralded the emergence of a new market for everyone. Just two years later, the motto of photokina was “digital total” and made it clear where future developments would go. 1994 is also seen as the "official" year of the start of digital photography in Germany, as the Vogelsänger studios announced the use of digital cameras. This announcement was particularly relevant because the Vogelsänger Studios - a large European photo studio in the field of interior photography - are known for their high quality standards for pictures, picture makers and tools. When one of the industry leaders in the field of advertising photography relied on digital camera technology, he paved the way for digital cameras in this country. However, with the initial high price for the first models of around DM 2,000 (around 1,600 euros based on today's purchasing power), consumers were reluctant to buy the new cameras in the following years.

PC and photo experts also carried out the following analysis in 1994: "For the often quoted average consumer , digital photography should only be of interest when well-known retail chains sell easy-to-use digital cameras as mass-produced goods on their shelves and the photo trade simultaneously offers the possibility of to produce inexpensive paper images for the electronic recordings - and this will in all likelihood still take some time. "

## Image generation

### Image transformation

In digital photography of the light waves into digital signals for conversion semiconductor - radiation detectors in CCD - or CMOS technology as image sensors used. This digitization of an analog image is an image conversion in which a discretization (breakdown into pixels) and quantization (conversion of the color information into a digital value) of the analog image are carried out.

### Hybrid process

A transitional solution between analog and digital photography is photography with the classic " silver film ", in which the negative or positive is first digitized with a scanner and then the stored image is digitally processed.

As a more cost-effective variant - since 1999 - so-called "high-resolution" (self-promotion) scans can be ordered together with the film development. The lower resolution recordings are saved on the CD supplied in the lossy JPG format. The quality of these scans is only suitable for viewing on the monitor, but not for further processing.

### In-camera image processing

Due to the architecture of the image recorder, an interpolation of the color and brightness values (so-called demosaicing ) is inevitably necessary in order to be able to display an image. This calculation and a number of other image changing processing processes such as the determination of the white balance , increase in the color saturation , raising the contrast , performing a tone correction, filtering (may cause u. A. A noise reduction), improvement of sharpness impression and possibly a lossy compression takes over the camera electronics and the firmware of the camera, if a JPEG image file (or a comparable file format) is to be saved directly to the memory card.

The camera-internal image processing can be bypassed with high-quality cameras by directly saving the metadata and the image-giving sensor data in a so-called RAW file ; this is a raw data format that is structured differently from manufacturer to manufacturer. This is often referred to as a "digital negative". With the RAW conversion , which is part of the post-production on the computer, an image is then interpolated from the measured values ​​stored in the raw data format and the processing steps described above that change the image are carried out (if necessary by the user "manually").

## Image properties

### Aspect ratio

Sensor size comparison

In digital compact cameras, the sensor has an aspect ratio of 1.33 (4: 3), so the images are also saved with this aspect ratio by default. In some cases, storage with other aspect ratios is also possible; this is mainly done by saving an image section.

This practice originally had historical reasons: The first digital cameras relied on existing sensors, and since 4: 3 corresponds to the aspect ratio of the common computer monitors and television standards NTSC , PAL and SECAM (which in turn derives from the earliest cinema films ), sensors with this aspect ratio were predominantly used available.

Digital camera systems, on the other hand, often use image sensors with an aspect ratio of 3: 2, which corresponds to that of 35mm film. Exceptions are the cameras of the Four Thirds and Pentax Q systems, which use the 4: 3 aspect ratio. Many cameras of the Micro Four Thirds system derived from the Four Thirds standard, as well as individual compact cameras, allow the selection of different aspect ratios, always using a section of a sensor surface that extends beyond the image circle of the lenses. This reduces the loss of resolution that would result from pure trimming.

### Number of pixels and resolution

The manufacturer specifies the number of image points, called pixels , on the one hand as a purely technical property of the sensor and, on the other hand, as the usable number of pixels. The latter usually corresponds to the maximum possible image resolution of the camera. The Bayer type sensor used in most cases, however, involves pixels that are provided with different color filters and are therefore only sensitive to sections of the light spectrum . The missing color information is interpolated from the surrounding pixels . With the Bayer sensor, half of the pixels have green and a quarter each have blue and red color filters. Variants in which half of the green color filters were replaced by turquoise ones have not caught on. This also applies to the Xenia sensor, which used the primary colors yellow, cyan and magenta.

With Bayer sensors with different pixel arrangements (e.g. rectangular pixels with the Nikon D1X or diagonally arranged pixels with the Super-CCD sensor from Fujifilm ), the images are output with the number of pixels that corresponds to the actual number of pixels, but still exists there is no longer a clear relationship between sensor pixels and image pixels. Super CCD sensors sometimes contain additional color-insensitive pixels that do not contribute to image resolution, but rather serve to increase the dynamic range .

In terms of the number of pixels, the Foveon X3 sensors are not directly comparable , as the surfaces of different color sensitivities are arranged on top of one another. So here every pixel has full color sensitivity, there is no need to interpolate the colors. It should be noted, however, that for marketing reasons, the number of pixels is often already tripled. Currently, the sensor is only used in Sigma brand cameras .

The number of pixels alone does not allow any statement about the achievable resolution, since the quality of the lens used is also important for this. When the image is output in JPEG file format, the processing of the image data in the camera also affects the resolution. In the case of digital compact cameras and mobile phones in particular , the actual image resolution often lags significantly behind the theoretical resolution resulting from the number of pixels. The reason for this lies in the small sensor dimensions and the commonly used lenses of simple construction and therefore limited imaging performance.

The resolution of digital images can only be compared to a limited extent with the resolution of a film negative or print, as losses can occur depending on the output medium. In addition, the resolution that is achievable today is by no means fully exploited for conventional output sizes such as printing up to postcard size or full screen display on screens.

The number of pixels does not necessarily reflect the resolution of fine structures. The Nyquist-Shannon sampling theorem applies to digitization . According to this, the maximum frequency that occurs in the image may not be more than half as high as the sampling frequency , because otherwise undesirable image distortions, for example moiré effects , occur and the original signal cannot be restored. ${\ displaystyle f _ {\ text {max}}}$${\ displaystyle f _ {\ text {scan}}}$

${\ displaystyle f _ {\ text {scan}}> 2 \ cdot f _ {\ text {max}}}$

Another limitation of the comparability of conventional and digital recordings results from the fact that the film grain is - technically speaking - a stochastic , i.e. a completely random and irregular noise , which, with the same technical resolution, is usually far less disturbing than the noise in the strictly regular pixel pattern of digital recordings. Visually, "analog" images with visible grain - with the same information content - appear either more bearable or disturbed.

In practice this means that you have to know or find out the maximum frequency before digitization and then the signal must be sampled at more than twice the frequency for digitization. In digital photography, in order to avoid the moiré effects from the outset, the optics can be slightly blurred. This corresponds to a low-pass filter . If the number of pixels in the sensor is increased, the optics must be readjusted, otherwise the increased number of pixels cannot be used. In practice, a so-called moiré filter is also used, which sits in the beam path and thus enables the use of perfectly matched optics.

When scanning rasterized images, the resolution must also be large enough that the finest structures of the raster can be displayed. You can then descreen (there are different functions for this) and then reduce the resolution.

### File format

The images resulting from digital photography, which are available in the form of digital data, are usually stored electronically, electromagnetically or optically; each picture corresponds to i. d. Usually a file that is usually saved in a standardized graphic format . Current digital cameras use JFIF ( JPEG compression), some of the better equipped also use the raw data format and TIFF . ImagePacs are created with hybrid processes such as the Kodak Photo CD . When scanning analogue originals, you usually have a free choice of the digital storage format.

The raw data format is recommended for maximum image quality in post-processing. In the past, image sensor data was saved uncompressed, but from 2005 lossless compressions became more common due to more powerful processors. However, this format requires significantly larger amounts of storage space and is used in particular in the professional environment.

JPEG, on the other hand, is lossy , but depending on the degree of compression it can be very economical in terms of storage space, but under favorable circumstances it can also be very close to the original. JPEG2000 now masters lossless compression and a larger color space, but is hardly supported for licensing reasons. The photographer has to make a decision about the degree of compression and thus about the possible richness of detail before taking the picture. The analog photographer makes a comparable preliminary decision when choosing the film material, and he has to change the same in order to achieve a different light sensitivity or film graininess , for example .

There are still many proprietary file formats that can no longer be easily read if the appropriate software is not available. Raw data critics note that you have to react accordingly, e.g. B. to convert them (conversion to an open or common file format, such as digital negatives (DNG)) or to secure the processing / development software of the time.

### Meta information

One of the advantages of digital image storage is the ability to save extensive meta information (or metadata ) in the file; This additional function is standardized in the Exchangeable Image File Format (Exif) and is implemented at least with basic data from all digital cameras.

The option of storing GPS position data when recording ( georeferencing ) in the metadata is only possible with appropriately equipped cameras, which usually rely on the connection of an external GPS receiver. The corresponding fields in the metadata can, however, also be filled in manually or using the appropriate programs. Some cameras also have an integrated compass that stores the direction in which the photos are looking.

The hybrid system APS already had comparatively limited options for storing meta-information, and even with 35mm cameras it is possible to insert time and date information as well as the image number on the film strip if the camera has a corresponding function. Some 35mm SLR cameras have the option of saving numerous recording parameters and outputting them to a text file; however, linking this data with the scanned image files is only possible manually.

With the Exif data embedded in the digital image file, it should be noted that some programs do not receive this data during image processing; this concerns z. B. older versions of the image editing software Adobe Photoshop .

## Digital recording technology

### Cameras and camera systems

Analog cameras and camera systems were developed and optimized over decades before their further development was discontinued by the market-leading manufacturers in recent years.

The operation of most analog 35mm cameras was similar - with autofocus, intervalometer, exposure metering, etc. differing significantly depending on the manufacturer. The use of buttons and menu systems in digital cameras can be significantly more extensive and complex and requires further knowledge beyond photochemistry - since many digital cameras offer many more functions than their mechanical predecessors. With digital photography, it is to be expected that the photographer can learn new things with every system change, while the basics always remain the same - such as aperture, focal length, shutter speed, etc.

The compatibility of the models with each other is very different. On the one hand, it depends on the manufacturer, on the model series and - especially in the case of simpler non-SLR models - often none or hardly any. Some manufacturers introduced completely new digital camera systems .

### Digital camera backs

Digital images can not only be made with native digital cameras or by digitizing analogue templates, but also with a digital camera back .

Scanbacks work on the principle of a flatbed scanner ; a distinction is made between single-shot and multi-shot processes .

### Effect of the lenses

In today's digital cameras, image sensors are usually built in with a smaller recording area compared to classic film formats . Due to the smaller image format, the angle of view of a lens is reduced for a given focal length , and the depth of field is smaller for a given f-number . This means that a lens with a focal length that is used as a normal lens for 35mm film has the angle of view of a telephoto lens for a digital camera with a smaller recording sensor . With the same angle of view and the same f-number, the range of depth of field increases.

The ratio of the normal image diagonal and the actual diagonal of the recording sensor is referred to as the " format factor " and is usually specified in the data sheet for the camera or lens. It describes the number by which you have to multiply the actual focal length of the lens of a camera in order to obtain a lens with the same angle of view for the 35mm format. For example, if the recording sensor is 12 mm × 18 mm in size, i.e. half the diagonal of the small picture format 24 mm × 36 mm, the format factor is 2. A lens of 25 mm on this digital camera has the same angle of view as a 50 mm lens on a small picture , and the same exposure time results with the same f-number. If the f-number is divided by the format factor, the result is the f-number at which the same depth of field is achieved.

## Digital recording practice

Compared to conventional photography, digital recording practice has some special features.

### Image composition

An example is the change in the depth of field , which results from the format factor (often incorrectly called focal length extension: the focal length of a lens does not change, only the angle of view used by the changed recording format ); Lenses, which are considered wide-angle in 35mm photography, appear as normal lenses in most digital cameras. Since the optical laws do not change, the effective depth of field (more precisely: the field of focus ) of the image increases. With digital cameras it is therefore more difficult than in 35mm photography to achieve a blurred image background, as is often desired in portrait and nude photography for design reasons. Some modern single-lens reflex digital cameras already have a full-frame sensor (24 mm × 36 mm). These cameras behave in exactly the same way as analog 35 mm SLR cameras.

### Special functions

Many digital cameras offer rotatable or swiveling displays with which some recording techniques are more convenient than with conventional cameras. These include, for example, shooting positions close to the ground, as they are often required in macro photography , or shots "overhead" in order to photograph over a crowd. The disadvantages of the displays are the high power consumption and the lack of visibility in bright surroundings (bright daylight).

Current digital cameras almost without exception offer the possibility of recording short video clips of around one minute in different formats from QQVGA or QVGA to WUXGA , usually with sound . A trend in digital photo technology can be observed to converge more and more with video technology; In top models, the length of the video clips is only limited by the capacity of the storage medium; the image resolution is in the range of quality from VHS to Blu-ray ( VGA , 640 × 480 or PAL, 720 × 576 or Full HD , 1920 × 1080 to UHD (4K) 4096 × 2160 pixels).

## Electronic image processing

In addition to the image processing carried out automatically by the camera, digital photography opens up numerous possibilities for image manipulation and optimization through electronic image processing , which go far beyond conventional image retouching and detail enlargement .

For example, panoramic photos can be conveniently assembled from a sequence of individual images , image backgrounds can be exchanged or people can be removed from images or copied into them.

## Storage and archiving

### Storage media for photography

Front and back of an SD card
SanDisk microSD SDXC 64 GB

As storage media in digital photography are usually memory cards used. The vast majority of these are SD cards ( Secure Digital Memory Card , also as SDHC and SDXC types). Company-specific card types such as Memory Stick ( Sony ) and xD-Picture Card ( Fujifilm and Olympus ) are of little importance . The somewhat larger CompactFlash cards (CF) were standard for a long time, but are now only required for a few high-quality SLR cameras. At times, microdrives were a compatible alternative for larger storage capacities to CompactFlash cards. Cell phones with a camera function usually save on microSD cards.

In the early days of digital photography, PC cards were used, but these, like cameras for SmartMedia cards, have completely disappeared from the market.

Digital compact cameras also often have internal memory that allows a small number of images to be stored without a memory card.

With some digital SLR cameras, remote control from a computer is also possible with the appropriate software . The storage can then take place directly on the hard drive of the computer, a memory card is then not required. The connection between the computer and the camera is made either by USB or SCSI cable or via WLAN . With some cameras it is also possible to send the image files via WLAN without remote control.

Memory cards are usually only used for temporary storage until the image files are transferred to a computer. They are then formatted and are then available again. In the event that larger amounts of data arise, the contents of the memory cards can first be transferred to image tanks , some of which also allow the images to be displayed. The files are later transferred from the image tanks to the computer.

Due to the possibility of remote control and the possibility of storing large amounts of images, digital photography was used early on under extreme climatic conditions, such as in space, deserts or polar regions.

### Storage media for archiving

In principle, the same requirements apply to long-term storage of image data that generally apply to the archiving of digital data . Another problem with image files is that the long-term readability of the files is not guaranteed when using RAW formats. So far (as of 2011), however, current programs are still available for all RAW formats ever used, with which the image files can be opened and further processed.

While a damaged original can be used for film, this is usually not possible with digital data, or only with a great deal of technical effort . The main advantage of digital data, unlike chemical film, is that any number of identical copies can be made. The transport of digital data is also much less complicated.

### Image databases

Analogous to conventional photography, there is the possibility of an index print in the form of thumbnails in a folder. Special programs for finding archived image files make it easier to search for images that, in the “analog world”, correspond to a well-maintained negative sorting system. While contact prints were still part of the normal workflow in analog photography , these techniques can be integrated into the operating system - even when saved in raw data format. A light table is thus superfluous.

The so-called image databases generate a preview image of the image and provide fields for describing the image and the recording situation; The metadata that is automatically recorded by the Exif format (date, time, focal length, aperture, etc.) provides a certain level of convenience . Many of these functions are already included in current operating systems. For ambitious photographers or professional photographers, online photo agencies are suitable platforms to save their photos and from there to sell them directly to buyers (newspapers, publishers, editorial offices, etc.). However, correspondingly large servers and storage spaces are required. In addition, "keywording" with suitable keywords is possible in order to find corresponding images from the databases. Due to the advantage of the computer technology, this only takes a fraction of the time required to search for image material for analog recordings. The IPTC fields saved in the image are used for keywording.

## presentation

Digital images can be presented as well as conventional photographs; there are more or less meaningful equivalents for almost all forms of presentation. The slide projection small audience, for example, replaced by the projection with a video projector ( video projector ); the photo album through the web gallery ; the framed photo through a special battery-operated display, etc.

If another image conversion ( D / A conversion ) is accepted, digital images can be printed out or exposed and then used just like conventional paper prints; even exposure on slide film is possible.

However, all current digital forms of presentation require sufficient technical knowledge as well as quite expensive technology; the cheapest video projector currently still costs about five times as much as a good slide projector . Another new problem is that of the calibration of the output device , which is possible with most monitors , but only with a few liquid crystal screens (LCDs) and can cause considerable effort, especially with beamers .

## Photo market

Due to the close relationship between digital photography on the one hand with video technology and on the other hand with information and communication technology , a number of new providers appeared on the photo market from the 1980s onwards, who were able to profitably use their know-how from the field of video and computer technology. Traditional photo providers entered into collaborations with electronics companies in order to avoid costly in-house developments.

Digital photography is becoming increasingly important in the photo industry. According to industry estimates, as early as 1999, in addition to 83 billion analog photographs, 10 billion digital images were produced. The industry association Bitkom reports that in 2006 around 58 percent of all Germans over 10 years of age used a digital camera.

According to the market research company Lyra Research, a total of 990,000 digital cameras were sold worldwide in 1996. In Germany, for the first time in 2003, more digital cameras were sold than analog cameras; According to statements from the retail sector, in some cases twice as many digital devices as analog cameras were sold in 2004. According to the Japanese industry association CIPA, around 121.5 million digital cameras were sold worldwide in 2010.

In addition to the expansion of digital photography into the mass market, there is a trend towards pushing back analog photography. For example, a large-scale displacement of photochemical products from the offerings of photo dealers and electronics stores has been observed since around 2004: the product range of photographic films declined significantly compared to the previous year. The development of new materials for photography on silver film does not stand still. A total of 23 new or improved film emulsions came onto the market between 2006 and 2008.

## Comparison with film-based photography

• With digital compact cameras, you can easily check the image section in live view mode with an electronic viewfinder or with the liquid crystal screen. Pivoting and rotating monitors simplify the control of unusual recording perspectives, for example from a frog's perspective or overhead.
• The photo stored in the non-volatile data memory can be checked immediately after the recording and, if necessary, deleted immediately, and further recordings can be made.
• The way to web or print publication of photos is shorter or faster because there is no need to scan slides or paper images. It is also possible to send individual images electronically to publishers and clients. If no other use of the recording is planned, you can set a relatively low image resolution and use the recording directly without further post-processing. Provided you have access to electronic media, photos can be exchanged and distributed quickly and easily.
• A film change for different lighting conditions is no longer necessary. Digital cameras can be easily adapted to the amount of light available; As with photography on film, the image quality decreases with increasing sensitivity .
• Digital cameras often offer the ability to make and play back simple video and sound recordings.
• Most digital cameras can be connected directly to electronic playback devices, such as televisions or video projectors , or to PictBridge- compatible photo printers.
• Very large numbers of digital images can be saved cost-effectively and in a very space-saving manner on small memory cards.
• The archiving of the digital image material is cheap and space-saving.

• Controversial durability of digital information (durability and long-term availability of storage media , data formats , drives , hardware and software ). In the case of recordings in proprietary storage formats in particular, the future usability of this data cannot be reliably estimated, as it is not known whether these formats will still be supported in the future. This applies both to the camera manufacturer-specific raw data formats and to the proprietary data formats of image processing software . With the DNG or OpenRAW formats, there are open standards for raw data, which, however, have not yet become widely accepted.
• With poor and older digital compact cameras, a clear shutter release delay can be determined, which is mainly caused by the fact that the image sensor is also evaluated for the autofocus.
• Camera displays can be difficult to read in bright surroundings, which makes finding a subject problematic, especially if the digital camera does not have an additional viewfinder.

## literature

• Caroline Butz, Tom Freiwah: Digital Photography . Picture by picture. Markt und Technik , Munich 2008, ISBN 978-3-8272-4261-7 .
• Chris George: Digital Photography. From beginner to professional . Mitp-Verlag 2006, ISBN 3-8266-1672-3 .
• Helmut Kraus, Romano Padeste: Digital high-end photography . Dpunkt Verlag, 2003, ISBN 3-89864-239-9 .
• David Pogue: Digital Photography. The missing manual. O'Reilly, Cologne 2009, ISBN 978-3-89721-912-0 .
• Josef Scheibel, Robert Scheibel: Understanding and using digital photography. vfv Verlag, 2010, ISBN 978-3-88955-192-4 .
• Alexander Trost: iKnow: digital photos. Data Becker, 2011, ISBN 978-3-8158-3703-0 .
• Christian Westphalen: The great photography school. Manual of digital photo practice. 2nd, corrected reprint of the 3rd, updated edition. Rheinwerk, Bonn 2018, ISBN 978-3-8362-4122-9 .

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