Talking about Digital Versus Film Photography

Both digital and film, have advantages and drawbacks and the different natures of these two technologies make the question of which is "better" meaningless without the qualifier "...for what purpose?" Strictly speaking, neither technology is better or worse. With that caveat in mind, this article attempts to compare some of the characteristics of both types of photography.

Quality

Spatial resolution

Many measures can be used to assess the quality of still photographs. The most discussed of these is the pixel count, presumed to correlate with spatial resolution. This is measured by the amount of picture elements (pixels) in the image sensor, usually counted in millions and called "megapixels".

The comparison of resolution between film and digital photography is complex. Measuring the resolution of both film and digital photographs involves numerous issues. For film, this issue depends on the size of film used (35 mm, Medium format or Large format), the speed of the film used and the quality of lens fitted to the camera. Since film is an analogue medium and has no pixels, its equivalent digital resolution is always an estimate.

Similarly, digital cameras have a variable relationship of resolution to 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. In addition, 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 grains.

Estimates of the resolution of a photograph taken with a 35 mm film camera vary. More information may be recorded if a finer grain film and/or developer are used. Conversely, less resolution may be recorded with poor quality optics or with courser-grained film.

Slow, fine-grained 35 mm B&W films with speeds of ISO 50 to 100 have estimated megapixel equivalents of 20 to 30 megapixels. Color films (both negative and slide types) are estimated between 8 and 12 megapixels. This would place film cameras (as of 2008) well over most point and shoot digital cameras. However, different films with the same ISO speeds can have different linear resolutions, so a direct comparison to digital is not easy. Resolution for 35mm film drops drastically with higher ISO ratings, particularly above ISO 400.

While 35 mm is oriented towards amateurs, many professional film cameras use medium format or large format films. Because of the size of the imaging area, have higher resolution than the current top-of-the-range digital cameras. It is estimated that a medium format film image can record around 50 megapixels, while large format films can record around 200 megapixels (4 5 inch) which would equate to around 800 megapixels on the largest common film format, 8 10 inches, without taking into account lens sharpness.

When deciding between film and digital and between different types of camera, it is necessary to consider the medium which will be used for display, and the viewing distance. For instance, if a photograph will only be viewed on a television or computer display (which can resolve only about .3 megapixels and 1-2 megapixels, respectively, as of 2009. HD sets of 1080p are around 2.07mp), then the resolution provided by a low-end digital cameras may be sufficient. For standard 4 6 inch prints, both analogue and digital formats may be adequate.

Noise and grain

With current technology, camera circuitry causes random noise in images taken by digital cameras, produced by thermal noise and manufacturing defects. Some digital cameras apply noise reduction to long exposure photographs to counteract this. For very long exposures it is necessary to operate the detector at low temperatures to avoid noise impacting the final image. Film grain is not affected by exposure time, although the relationship between film sensitivity and exposure time changes with exposures longer than one second, a phenomenon known as reciprocity failure.

Dynamic range

The topic of dynamic range is complex. Comparisons between film and digital media should consider:

What film? For example, low-contrast print film has greater DR than slide film's low DR but richer gradation in recorded tones.
What film format? Larger formats give greater film to image ratio so grain is less detectable at film's limits of exposure.
What sensor? The more convenient pocket digicams use smaller sensors which generate more sensor noise.
What scanner? Variations in optics, sensor resolution, scanner DR, and precision of the analog to digital conversion circuit can make a huge difference.
What counts as image and what is noise? This question defines the limits of DR 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.

Some amateur authors have performed tests with inconclusive results. R. N. Clark, comparing a professional digital camera with 35mm film, reached the conclusion 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 comes to 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."

Finally, 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 DR."

The digital camera industry is attempting to address the problem of dynamic range. Some CCDs like Fujifilm's Super CCD combines photo sites of different sizes to give increased dynamic range. Other manufacturers use in-camera software to prevent highlight overexposure. Nikon calls this feature D-Lighting. However, D-Lighting often produces unnatural halos in the images.

Drawing showing the relative sizes of sensors used in most current digital cameras.

Effects of sensor size

Sensor Sizes
Drawing showing the relative sizes of sensors used in most current digital cameras.
All Digital Camera Review by Gene Wrights, and most digital SLRs, have sensors that are smaller than a 36 mm x 24 mm frame of 35 mm film. This affects aspects of the captured image and the way the camera is used. These effects include:
  • Increased depth of field;
  • Decreased light sensitivity and increased pixel noise;
  • For digital SLRs, cropping of the field of view when using lenses designed for 35 mm camera;
  • Lenses may be smaller because they only need to project their image onto a smaller area;
  • Increased degree of enlargement of the final image.
The depth of field of a camera and lens combination increases as the imaging area decreases, for a given f-number. This may have advantages for Digital Camera Review by Gene Wrights since they are intended for taking snapshots. More of the image will be in focus than with a larger sensor, and the autofocus system does not need to be as accurate to produce an acceptable image. Conversely, photographers often limit depth of field to create certain effects, such as isolating a subject from its background. Cameras with imaging areas smaller than 36 mm x 24 mm require a wider aperture on the lens to achieve the same degree of selective focusing.

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 increase, the size of the individual pixels has to decrease. This smaller pixel size means that each one collects less light and the resulting signal is amplified more to produce the final value. This also amplifies any noise. With a smaller signal, the signal-to-noise ratio decreases. More noise is present in the image, and the higher noise floor means that less useful information is extracted from the darker parts of the image.

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 while 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 normally higher.

Only expensive digital SLRs have full-frame sensors that are 36mm 24 mm, which eliminate depth of field and crop factor problems when compared to 35 mm film cameras.

The smaller sensor size of digital compact 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 even have a negative effect on the overall resolution because of increased noise reduction.

Convenience and flexibility

Digital photography is flexible to the extreme; a photographer can change anything about a photograph after it has been taken. These two pictures are a before and after demonstrating the capabilities of the digital photographer. Flexibility and convenience have has been the major drivers of the widespread adoption of digital cameras. With film cameras, the roll of film is normally completely exposed before being processed. Only once the film is returned is it possible to see the photograph. Most digital cameras incorporate a liquid crystal display that allows the image to be viewed immediately after exposure. The photographer may delete undesired or unnecessary photographs, allowing the photographer an immediate opportunity to repeat the image. When a user desires prints, it is only necessary to print the good photographs.

With digital imaging, images may be conveniently stored on a personal computer for modification. Professional-grade digital cameras can store pictures in a raw image format which stores the output from the sensor directly rather than processing it immediately to 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 of the image, such as contrast, sharpness or color balance, before producing a final image. Alternatively, users may retouch the content of recorded JPEG images; software for this purpose may be provided with consumer-grade cameras. (See Digital image editing.)

Digital photography allows the collection of large amounts of archival documents in a short period of time which has many benefits for the researcher including convenience, saving money and an increased flexibility in using the documents.

Price

Film and digital imaging systems have different cost emphases. With digital photography, cameras tend to be significantly more expensive than film equivalents. With digital cameras, taking photographs is effectively cost-free. The price of digital cameras continues to fall and using film may be seen as more expensive than digital.

High quality film cameras are less complicated and therefore less expensive. The major expenses are ongoing film and processing costs. The photographer will only identify unsuitable images after developing and printing have been paid for.

Film offers the photographer more control over the depth-of-field than a DSLR with a APS sensor, and the cost of full-frame sensor cameras may be very high. 35mm single-lens reflex cameras may be purchased for a fraction of the price of a full-frame DSLR. Some lenses are interchangeable between digital and film cameras; film can be an attractive introduction to photography because of this.

The costs associated with digital photography are specialist batteries, memory cards, paper, printer ink cartridges and long-term storage.

With many photographers switching to digital, film cameras and lenses are now available on the second-hand market at often much-reduced prices.

Cleanliness

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. There is a risk of debris in the camera, such as dust or sand, scratching 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 easy to rectify using a computer with photo editing software available. 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, most notably models like Pentax's K20d, incorporate extensive dust and weather seals to avoid this problem.

Archiving

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 of the base material.

The archival potential of digital photographs is less well understood because digital media have existed for 50 years. Three issues are involved for archival storage: physical stability of the recording medium, future readability of the storage medium and future readability of the file formats used for storage.

Many types of digital media are not capable of storing data for prolonged periods of time. Magnetic disks and tapes may lose their data after twenty years, flash memory cards even less. Good quality optical media may be the most durable storage media for digital data.

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 short lifespan of digital technologies often causes the drives to read media to become unavailable. For example, the first 5-inch Floppy disks were first made available in 1976. However, the drives to read them are already extremely rare 30 years later.

The ability to decode the data is important. Digital cameras save photographs in JPEG format, that has existed for approximately 15 years. Because the instructions on how to decode this format are publicly known, it is unlikely that this files will be unreadable 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 at any time for economic reasons. This could make it difficult to read these 'raw' files in the future, unless the camera makers were to release information on the file formats.

However, digital archives have several methods of overcoming such obstacles. In order to counteract the file format problems, many organizations prefer to choose an open and popular file format. Doing so increases the chance that software will exist to decode the file in the future.

Additionally many organizations take an active approach to archiving rather than relying on formats being readable decades later. This takes advantage of the ability to make perfect copies of digital media. So, for example, rather than leaving data on a format which may potentially become unreadable or unsupported, the information can typically be copied to newer media without loss of quality. This is only possible with digital media.

Digital images may be printed and stored like traditional photographs.

Integrity

Film produces a first generation image, which contains only the information admitted through the aperture of the camera.

Film images are very difficult to fabricate, As a result in law enforcement and in cases 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, there are digital cameras that 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. 

Nikon film scanner, right, which images 35mm film for digital input.

Converting film to digital

Film photographs may be digitally scanned into a computer with a scanner. They may then be manipulated as are other digital images.

There are currently three ways to scan a film image into a computer.  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 also be used to scan reflective and transparent images.

The second method is to use a dedicated film scanner, such as the Nikon Coolscan (pictured) which 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.

The third method is to take a digital photograph of the source image by mounting a digital camera on a copy stand and photographing the source image. It is also possible to use a slide projector to project the image from a transparency and then take a digital photograph of the projection.

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