- Digital versus film photography
Digital versus film photography has been a topic of debate since the invention of digital cameras towards the end of the 20th Century. Both digital and film photography have advantages and drawbacks. 21st century photography is dominated by digital operation, but the older photochemical methods continue to serve many users and applications.
The quality of digital photographs can be measured in several ways. Pixel count is presumed to correlate with spatial resolution. The quantity of picture elements (pixels) in the image sensor is usually counted in millions and called "megapixels" and often used as a figure of merit. The resolution of film images depends upon the area of film used to record the image (35 mm, Medium format or Large format), the speed of the film and the quality of lens fitted to the camera.
Digital cameras have a variable relationship between final output image resolution and sensor megapixel count; other factors are important in digital camera resolution, such as the number of pixels used to resolve the image, the effect of the Bayer pattern or other sensor filters on the digital sensor and the image processing algorithm used to interpolate sensor pixels to image pixels. Digital sensors are generally arranged in a rectangular grid pattern, making images susceptible to moire pattern artifacts, whereas film is not affected by this because of the random orientation of its grains.
Estimates of a photograph's resolution taken with a 35 mm film camera vary. More information may be recorded if a fine-grain film, combined with a specially formulated developer, are used. Conversely, use of poor quality optics or coarse-grained film yield lower image resolution . A 36 mm x 24 mm frame of ISO 100-speed film was initially estimated to contain the equivalent of 20 million pixels,, although this estimation was later revised to between 4 and 16 million pixel depending on the type of film used. 
Many professional-quality film cameras use medium format or large format films. Because of the size of the imaging area, these can record higher resolution images than current top-of-the-range digital cameras. A medium format film image can record an equivalent of approximately 50 megapixels, while large format films can record around 200 megapixels (4 × 5 inch) which equates to around 800 megapixels on the largest common film format, 8 × 10 inches, without accounting for lens sharpness. A medium format DSLR provides from 42 to 50 megapixels, but cannot be enlarged with the same level of detail as medium format film.
Thus film and digital work each provide a wide range of performance in this regard, overlapping but with film tending to higher resolution.
The medium which will be used for display, and the viewing distance, should be taken into account. For instance, if a photograph will only be viewed on an old analog television or modern HDTV set of 1080p that can resolve approximately 0.3 megapixel and 2 megapixels, respectively, the resolution provided by high-end camera phones may suffice, and inexpensive compact cameras usually will. Similar or more expensive hardware may also fill the screens of computer displays, though those few that show tens of megapixels will be out of reach of low-end film photography and all but specialized scientific or industrial digital cameras.
Noise and grain
Thermal noise, produced by heat and manufacturing defects, degrades shadow areas of electronic images with random pixels of the incorrect colour. Film grain becomes obvious in areas of even and delicate tone. Grain and film sensitivity are linked, with more sensitive films having more obvious grain. Likewise, when used at high sensitivity settings, digital camera images show more image noise than those made at lower sensitivities.
However, even if both techniques have inherent noise, it is widely appreciated that for color, digital photography has much less noise/grain than film at equivalent sensitivity, leading to an edge in image quality. For black-and-white photography, grain takes a more positive role in image quality, and such comparisons are less valid.
Noise is a particularly critical issue with digital cameras, often producing colour distortion or confetti, occurring most severely on the blue component and least severely on the red component.
Nearly all digital cameras apply noise reduction to long exposure photographs to counteract thermal noise. For very long exposures, the image sensor must be operated at low temperatures to prevent noise affecting the final image. Film grain is not affected by exposure time, although the apparent speed of the film changes with lengthy exposures, a phenomenon known as reciprocity failure.
- Film type: For example, low-contrast print film has greater dynamic range than slide film's low dynamic range and higher contrast.
- Data format: Raw image format or JPEG?
- Pixel density of the sensor: The large sensors in DSLRs and medium format digital cameras generally have larger photosites which collect more light and therefore are generally more sensitive than their diminutive counterparts in compact digital cameras. The larger sensors tend to have better signal to noise characteristics. However signal processing and amplification improves with generation and small sensors of today approach the dynamic range of large sensors in the past.
- Scanner: Variations in optics, sensor resolution, scanner dynamic range and precision of the analogue to digital conversion circuit cause variations in image quality.
- Optical versus digital prints: Prints differ between media and between images shown on VDUs.
- Signal/noise ratio: This defines the limits of dynamic range within a single photograph, and may vary with subject matter. A single comparison cannot demonstrate that digital or film has a smaller or greater dynamic range.
Dynamic range is of considerable importance to image quality in both the digital and emulsion domain. Both film and digital sensors exhibit non-linear responses to the amount of light, and at the edges of the dynamic range, close to underexposure and overexposure the media will exhibit particularly non-linear responses. The non-linear dynamic response or saturation qualities of emulsion film are often considered a desirable effect by photographers, and the distortion of colour, contrast and brightness varies considerably between film stocks. There is no limit to the number of possible levels of colour on emulsion film, whereas a digital sensor stores integer numbers, producing a limited and specific possible number of colours. Banding may be visible in the unusual case that it is not obscured by noise, and detail may be lost, particularly in shadow and highlight areas.
Some amateur authors have performed tests with inconclusive results. R. N. Clark, comparing a professional digital camera with 35 mm film, concluded that "Digital cameras, like the Canon 1D Mark II, show a huge dynamic range compared to either print or slide film, at least for the films compared."
Ken Rockwell reached a different conclusion: "CCDs and the related capture electronics will need about ten times more dynamic range (three stops) than they have today to be able to simulate film's shoulder....This is the biggest image defect in digital cameras today."
Carson Wilson informally compared Kodak Gold 200 film with a Nikon D60 digital camera and concluded that "In this test a high-end consumer digicam fell short of normal consumer color print film in the area of dynamic range."
The digital camera industry is attempting to address the problem of dynamic range. Some cameras have an automatic exposure bracketing mode, to be used in conjunction with high dynamic range imaging software. Some CCDs including Fujifilm's Super CCD combine photosites of different sizes to give increased dynamic range. Other manufacturers use in-camera software to prevent highlight overexposure. Nikon calls this feature D-Lighting.
Presentation technology is also relevant, as different color printing methods, cathode-ray tubes, LCDs and other displays all have different dynamic range limits and degrees of linearity.
Effects of sensor size
- Depth of field;
- Light sensitivity and pixel noise;
- Relative cropping of the field of view when using lenses designed for 35 mm camera;
- Optimizing lens design for smaller sensor area;
- Increased relative enlargement of the captured image.
Depth of field is often quoted as being greater for digital cameras than for film cameras. The maxim packages several counterintuitive aspects of photography into a single (largely correct) theorem.
Depth of field, for a given lens focal length, at a given f-number will scale with sensor (film/chip) size. In effect, a smaller sensor will increase the apparent depth of field because it magnifies the portion of the image that is in focus.
However, manufacturers are increasingly using (especially in the budget digital camera market) "35 millimeter equivalent" focal lengths for lenses. This gives rise to the "depth of field is greater for digital cameras" myth: the shorter the focal length of a lens, the greater is its depth of field (at fixed F-stop). Therefore, if a sensor that is one-fourth the width and height of a 24 x 36 mm frame of film is exposed to an image through a lens that is correspondingly one-fourth the focal length, the depth of field increases 16x (scaling per the square of focal length) on an absolute scale, but 4x from a comparison-of-images perspective (the imaging dimension is 4x smaller).
This increase in relative depth-of-field may have advantages for taking snapshots; more image will be in focus than with a larger sensor and an autofocus system inaccuracies are less critical to produce an acceptable image. Contrarily, photographers wishing to decrease depth of field to create certain effects, such as isolating subjects from their background need to increase aperature when sensors smaller than 36 mm x 24 mm to achieve the same degree of selective focusing. Depth of field can be minimized by use of large format cameras, which are very rarely digital.
Light sensitivity and pixel noise are both related to pixel size, which is in turn related to sensor size and resolution. As the resolution of sensors (of a specific format) increase, the size of the individual pixels naturally has to decrease. This smaller pixel size means that each pixel collects less light and the resulting signal must be amplified more to produce the final value. Noise is also amplified and the signal-to-noise ratio decreases, and the higher noise floor means that less useful information is extracted from the darker parts of the image.
Countering these effects of digital-signal noise are advances being made in sensor technology itself. Currently (2010) the top-end of digital sensor sensitivity is at ISO 102,400 (both Canon and Nikon), whereas the run-of-the-mill prosumer DSLR and ILC cameras offer sensitivities greater than ISO 6400, often with good noise performance at one-quarter maximum sensitivity.
Some digital SLRs use lens mounts originally designed for film cameras. If the camera has a smaller imaging area than the lens' intended film frame, its field of view is cropped. This crop factor is often called a "focal length multiplier" because the effect can be calculated by multiplying the focal length of the lens. For lenses that are not designed for a smaller imaging area whilst using the 35 mm-compatible lens mount, this has the beneficial side effect of only using the centre part of the lens, where the image quality is in some aspects higher. Only expensive digital SLRs and very rarely expensive 'compacts' have 36mm × 24 mm sensors, eliminating depth of field and crop factor problems when compared to 35 mm film cameras.
The smaller sensor size of digital compact cameras means that prints are extreme enlargements of the original image, and that the lens must perform well in order to provide enough resolution to match the tiny pixels on the sensor. Most digital compacts have sensors that exceed the maximum resolution that the lens is capable of delivering. Increased sensor resolution may have an effect upon the image resolution because of increased noise reduction.
Dust on the image plane is a constant issue for photographers. DSLR cameras are especially prone to dust problems because the sensor remains in place, where a film advances through the camera for each exposure. Debris in the camera, such as dust or sand, may scratch the film; a single grain of sand can damage a whole roll of film. As film cameras age, they can develop burs in their rollers. With a digital SLR, dust is difficult to avoid but is easy to rectify using a computer with image-editing software. Some digital SLRs have systems that remove dust from the sensor by vibrating or knocking it, sometimes in conjunction with software that remembers where dust is located and removes dust-affected pixels from images.
Compact digital cameras are fitted with fixed lenses; dust is excluded from the imaging area. Similar film cameras are often only light-tight and not environmentally sealed. Some modern DSLRs, like the Olympus E-3, incorporate extensive dust and weather seals to avoid this problem.
Film produces a first generation image, which contains only the information admitted through the aperture of the camera. Trick photography is more difficult with film; in law enforcement and where the authenticity of an image is important, like passport or visa photographs, film provides greater security over most digital cameras, as digital files may have been modified using a computer. However, some digital cameras can produce authenticated images. If someone modifies an authenticated image, it can be determined with special software. SanDisk claims to have developed a write-once memory stick for cameras, and that the images once written cannot be altered.
From an artistically conservative standpoint, some practitioners believe that the use of film offers a more authentic mode of expression than with easily enhanced digital images. As with the earlier transition from oil painting to photography, or from photographic plates to film photography, older methods are more expensive, thus encourage more selectivity and additional consideration.
Film and digital imaging systems have different cost emphases. Digital cameras are significantly more expensive than film equivalents, but taking photographs with them is effectively cost-free. Other costs of digital photography include specialist batteries, memory cards and long-term data storage. Inkjet printers can make low-quality prints cheaply and easily from digital files, but high-quality printing has high costs regardless of image source.
Converting film to digital
Film photographs may be scanned into a computer with a scanner, after which they may be manipulated as digital images. Several methods are available:
- A reflective image scanner may be used; inexpensive flatbed scanners can scan an image on paper media.
- An expensive and very high resolution drum scanner can scan reflective and transparent media, and often uses a vacuum tube called a "photomultiplier" which exhibits much less noise and greater vibrancy than a CCD.
- A Flying spot scanner can scan reels of film quickly.
- A dedicated film scanner, such as the Nikon Coolscan (pictured), can scan 35 mm transparencies and negatives. Other film scanners can scan 120 film, typically up to 6 x 7 cm or 6 x 9 cm.
- A digital camera on a copy stand can photograph the source image.
- A slide projector can project the image from a transparency onto a screen, so the digital camera can photograph it.
Films and prints, processed and stored in ideal conditions, may remain substantially unchanged for more than 100 years. Gold or platinum toned prints may have a lifespan limited by that of the base material.
The archival potential of digital images is poorly understood because digital media have existed for 50 years. The physical stability of the recording medium, future readability of the storage medium and future readability of the file formats used for storage are issues to be considered. Some types of digital media are incapable of storing data for prolonged periods. According to proponents of digital media magnetic disks and tapes will lose their data after twenty years, although in practice properly stored magnetic media will last far longer, perhaps hundreds of years. However flash memory cards may lose their data in fewer than twenty years. Good quality optical media may be the most durable digital storage media.
It is important to consider the future readability of storage media. Assuming the storage media can continue to hold data for prolonged periods of time. The equipment necessary to read media may become unavailable. For example, 5¼-inch floppy disks were first made available in 1976 but the drives to read them are already extremely rare. Also lower density floppy disk formats (e.g. 360k) prove to be more readily readable 25 years later.
The ability to decode the data is important. Digital cameras save photographs in JPEG format, which has existed for approximately 15 years. Because the instructions on how to decode this format are publicly known, it is likely that these files will be readable in the future.
Most professional cameras can save in a Raw image format, the future of which is less certain. Some of these formats contain proprietary data which is encrypted or protected by patents, and could be abandoned by their makers for economic or other reasons, causing possible future difficulty in decoding these files unless the camera makers were to release information on the file formats.
In order to counteract the file format problems, many organizations prefer to choose an open and popular file format, increasing the chance that software will exist to decode the file in the future. Many organizations take an active approach to archiving rather than relying on the future readability of digital files, relying upon the ability to make perfect copies of digital media. Rather than leaving data on in format which may potentially become unreadable or unsupported, the information can be copied to newer media without loss of quality. Digital images may also be printed and stored like other printed photos.
Convenience and flexibility
Flexibility and convenience are among the reasons for the widespread adoption of digital cameras. With film cameras, a roll is usually completely exposed before being processed. When the film is returned it is possible to see the photograph, but most digital cameras incorporate a liquid crystal display that allows the image to be viewed immediately after capture. The photographer may delete undesired or unnecessary photographs, or reshoot the image if required. A user who wants prints can quickly and easily print just the required photographs.
Photographic film is made with specific characteristics of Color temperature and sensitivity (ISO). Lighting conditions often require characteristics different from those of the film specifications, requiring the use of filters or corrections in processing. Digital photography allows color temperature and sensitivity to be adjusted at each shot, either manually or automatically.
Digital images may be conveniently stored on a personal computer or in off-line storage such as small memory cards. Professional-grade digital cameras can store pictures in a raw image format, which stores the output from the sensor rather than processing it immediately to form an image. When edited in suitable software, such as Adobe Photoshop or the GNU program GIMP (which uses dcraw to read raw files), the user may manipulate certain parameters, such as contrast, sharpness or color balance before producing an image. JPEG images can be similarly manipulated, though usually less precisely; software for this purpose may be provided with consumer-grade cameras.
Digital photography allows the quick collection of a large quantity of archival documents, bringing convenience, lower cost and increased flexibility in using the documents.
For large format and ultra large format photography, film may have some advantages over digital cameras, such as price and flexibility, when used outside the studio environment. Digital rotating line cameras provide similarly high performance, but scan mechanically rather than use a single sensor, making them expensive, large, and rarely moved.
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- ^ Resolution Test Area 2: trees and Mountains R. N. Clark, 8 April 2001. Retrieved 2 September 2006.
- ^ Why do Images Look Crappy Played on a TV
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- ^ Dante Stella. "More is Less is More: The Devil is in the Dynamic Range". DanteStella.com online article, retrieved 2008. http://www.dantestella.com/technical/dynamic.html.
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- ^ Carson Wilson. "Real World Test: Kodak Gold 200 vs Nikon D60 Dynamic Range". apples.carsonwilson.com online article, September 13, 2008. http://apples.carsonwilson.com/index.php?/archives/36-Real-World-Test-Kodak-Gold-200-vs-Nikon-D60-Dynamic-Range.html.
- ^ a b Bob Atkins. "Size Matters". Photo.Net Equipment Article, 2003. http://photo.net/equipment/digital/sensorsize.
- ^ Bob Atkins. "Digital Depth of Field". BobAtikins.com. http://www.bobatkins.com/photography/technical/digitaldof.htmle. 
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- ^ Dean M. Chriss. "RAW Facts: The short life of today's RAW files: Demystifying the Debacle". DMCPhoto online article, April 29, 2005. http://www.dmcphoto.com/Articles/RAW1/index.html.
- ^ http://www.physorg.com/news139751840.html,Accelerated research using a digital camera
- Published Comparisons: Film versus Digital Photography
- Digital vs. Film (The Real Deal) - Nikon D300 vs. Fuji GS645s
- DIGITAL SLR vs. FILM SCANS
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