Quality
[edit] Spatial resolution
There are many measures that can be used to assess the quality of still photographs. The most discussed of these is spatial resolution, i.e. the number of separate points in the photograph.[citation needed] This is measured by how many picture cells make up the photo, usually counted in the millions and hence called "megapixels".[citation needed]
The comparison of resolution between film and digital photography is complex. Measuring the resolution of both film and digital photographs depends on 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 lenses in the camera. Additionally, since film is an analogue medium, it does not have pixels so its resolution measured in pixels can only be an estimate.
Similarly, digital cameras rarely perform to their stated megapixel count.[citation needed] Other factors are important in digital camera resolution such as the actual number of pixels used to store 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 pattern, making images susceptible to moire pattern artifacts, whereas film is immune to such effects due to the random orientation of grains.[citation needed]
Estimates of the resolution of a photograph taken with a 35 mm film camera vary. It is possible for more resolution to be recorded if, for example, a finer grain film and/or developer are used or less resolution to be recorded with poor quality optics or low light levels. The digital megapixel equivalent of film is highly variable and roughly depends on film speed. 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 almost all 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.[citation needed]
While 35 mm is the standard format for consumer cameras, many professional film cameras use Medium format or Large format (generally sheet) films which, due to the size of the film used, can boast resolution many times greater than the current top-of-the-range digital cameras. For example, it is estimated that a medium format film photograph can record around 50 megapixels, while large format films can record around 200 megapixels (4 × 5 inch)[1] which would equate to around 800 megapixels on the largest common film format, 8 × 10 inches. However, the estimate above does not take into account lens sharpness.[citation needed]
The question of photo quality often comes up when attempting to print a digital image at various sizes. The following tables can aid the consumer in determining a maximum photo print size based upon the megapixel depth[2]:
MegaPixel
Size | Image Resolution | Outstanding Print
fine compression | Very Good Print | Fair Print |
| 1 | 480 x 640 | - - - - | Wallets | Up to 4x6 |
| 1.2 | 768 x 1024 | Wallets | Up to 4x6 | Up to 5x7 |
| 1.5 | 1024 x 1280 | Up to 3x5 | Up to 5x7 | Up to 8x10 |
| 2 | 1200 x 1600 | Up to 4x6 | Up to 8x10 | Up to 10x15 |
| 3 | 1536 x 2048 | Up to 5x7 | Up to 8x12 | Up to 12x18 |
| 4 | 1800 x 2400 | Up to 6x9 | Up to 11x14 | Up to 16x20 |
| 5 | 1932 x 2580 | Up to 6x9 | Up to 12x18 | Up to 16x24 |
| 6 | 2016 x 3040 | Up to 8x10 | Up to 12x18 | Up to 20x30 |
| 7.1 | 2304 x 3072 | Up to 8x10 | Up to 16x24 | Up to 24x36 |
| 8.3 | 2336 x 3504 | Up to 10x15 | Up to 20x30 | Up to 30x40 |
| 10.2 | 2592 x 3872 | Up to 11x14 | Up to 24x30 | Up to 30x40 |
| 10.9 | 2704 x 4060 | Up to 11x14 | Up to 24x36 | Up to 36x48 |
| 16.6 | 3328 x 4992 | Up to 12x18 | Up to 36x48 | Up to 48x64 |
When deciding between film and digital and between different types of camera you want to use for a given project, it is necessary to take into account 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[3] and 1-2 megapixels, respectively, as of 2008. HD sets of 1080p are around 1.8mp), then the resolution provided by a low-end digital cameras may be sufficient. For standard 4 × 6 inch prints, it is debatable whether there will be any perceived quality difference between digital and film when it comes to resolution. However color film will generally have the ability to reproduce a much wider range of colors than digital sensors smaller than 3 megapixels. The difference is visible on most modern computer monitors and on traditional chemically processed prints, but may not be noticeable on output media with limited color pallets such as lower end desktop inkjet prints and even large media such as billboards. Comparisons can depend on the gamut of the output media, which can influence the perception of resolution. An output media with a smaller gamut will need to use more dpi to reproduce a given color.
[edit] Noise levels
It should be noted that a special case exists for long exposure photography - Currently available technology contributes random noise to the 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 apparent speed of the film does change with longer exposures, a phenomenon known as reciprocity failure.[citation needed]
[edit] Dynamic range
As of early 2008, many current DSLRs offer a dynamic range that is as wide or wider than film such as the Canon 5D[4], 30D[5], 40D[6], Nikon D40[7], D40x[8], D80[9], D200 [10]), and Sony A700.[11] CCDs such as Fuji's Super CCD, which combines photosites of different sizes, have also addressed this problem with a gain of a much as 3 stops of range, but this has been at the expense of decreased actual resolution.[12]
Drawing showing the relative sizes of sensors used in most current digital cameras.
[edit] Effects of sensor size
Most digital cameras, even most digital SLRs, have sensors that are smaller than a standard frame of 35 mm film. These smaller sensors have a number of effects on the captured image and the use of the camera:[13]
- 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 can be smaller, since they only need to project light onto a smaller image area
- Increased degree of enlargement.
The depth of field of a camera/lens combination increases as the film/sensor size decreases. This is arguably an advantage for compact digital cameras since they are intended for taking snapshots. It means that more of the scene will be in focus than with a larger sensor, and the autofocus system does not need to be as accurate to capture an acceptable image. However, art photography often makes use of a limited depth of field to create special effects, such as isolating a subject from the background. When using a digital camera with a small sensor, the photographer would have to use a larger aperture on the lens to achieve similar amounts of "bokeh".[citation needed]
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 amplification also includes an amount of noise in the signal. With a smaller signal, the signal-to-noise ratio decreases. Not only is more noise present in the image (relatively speaking), but the relatively higher noise floor means that less useful information can be extracted from the darker parts of the image.[13]
Most digital SLRs use lens mounts originally designed for film cameras, commonly 35 mm. If the camera has a smaller sensor than the intended film frame, the field of view of the lens is cropped. This crop factor is often called a "focal length multiplier" since the effect can be simplified to that of multiplying the focal length of the lens. For lenses that are not "digital specific" (designed for a smaller sensor despite using the 35 mm-compatible lens mount) this has the slight beneficial side effect of only using the center part of the lens, where the image quality is normally best; the "soft edges" are cropped off.[citation needed]
Only a few of the most expensive digital SLRs have so-called "full-frame" sensors — a sensor the same size as a 35 mm film frame (36 × 24 mm). These larger sensors eliminate the issues of depth of field and crop factor when compared to 35 mm film cameras.[citation needed]
With compact digital cameras the sensors are tiny compared to DSLRs. This means that prints are extreme enlargements of the original image, and that the lens has to perform outstandingly in order to provide enough resolution to match the tiny pixels on the sensor. However, many modern compact camera lenses, even 12x "super-zoom" designs, achieve the needed sharpness. The use of a small sensor also has the effect of increasing depth of field to the extent of making images very "flat" looking because backgrounds can not be blurred except for subjects very close to the camera.[citation needed]
[edit] 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.
This has been one of the major drivers of the widespread adoption of digital cameras.[citation needed] Before the advent of digital cameras, once a photograph was taken, the roll of film would need to be finished and sent off to a lab to be developed. Only once the film was returned was it possible to see the photograph. However, most digital cameras incorporate an LCD screen which allows the photograph to be viewed immediately after it has been taken. This allows the photographer to delete undesired or unnecessary photographs, and offers an immediate opportunity to re-take. When a user desires prints, it is only necessary to print the good photographs.
Another major advantage of digital technology is that photographs can be conveniently moved to a personal computer for modification. Many professional-grade digital cameras are capable of storing pictures in a Camera RAW 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 dcraw, the photographer can manipulate certain parameters of the taken photograph (such as contrast, sharpness or color balance) before it is "developed" into a final image. Less sophisticated users may choose to simply "touch up" the actual content of the recorded image;[citation needed] software with which to do this is often provided with consumer-grade cameras. (See Digital image editing.)
The two formats (film and digital) have different cost emphases. With digital photography, cameras tend to be significantly more expensive than film ones,[citation needed] comparing like for like. This is offset by the fact that taking photographs is effectively cost-free.
With film photography, good-quality cameras tend to be less complicated and, therefore, less expensive, but at the expense of ongoing film and in particular processing costs. The photographer will also only identify poor shots after paying developing and printing costs.
35mm film does offer the photographer much more control over the depth-of-film than a 'crop' body DSLR, and the entry cost differential to full-frame photography can therefore be very large - 35mm SLR's can be purchased for a tenth of the price of a full-frame DSLR. Since the lenses from the main brands are interchangable between SLR and DSLRs, film can still be an attractive route into photography because of this.
There are also additional costs associated with digital photography, such as specialist batteries, memory cards, and long-term storage. However these combined are likely to be very much less than developing costs.
With many photographers switching to digital, many film cameras (and associated equipment like lenses) are now available on the second-hand market (especially online auction sites like eBay) at often very reduced prices.
[edit] Robustness
Dust on the image plane is a constant issue for photographers. DSLR cameras are especially prone to dust problems because the sensor is reused for every shot, where a film SLR will effectively have a new "sensor" slid into place for every shot. A fresh, dust free film frame comes at risk of debris such as dust or sand in the camera scratching the film. A single grain of sand can damage a whole roll of film. Also as film SLRs age, they can develop burs in their rollers. With a digital SLRs dust is difficult to avoid, but easy rectify if one has a computer with photo editing software available. Some digital SLRs have systems that remove dust from the sensor by vibrating or knocking the sensor. Some cameras do this in conjunction with software that remembers where dust is located on the sensor and removes dust-affected pixels from images.[citation needed]
One huge advantage to compact point and shoot digital cameras is that they are exclusively available with fixed lenses, so dust is not an issue for them. This is not true of point an shoot film cameras, which are often only light tight and not environmentally sealed.
[edit] Archiving
When choosing between film and digital formats, one may need to consider the suitability of each as an archival medium.[citation needed]
Films and prints processed and stored in ideal conditions have demonstrated an ability to remain substantially unchanged for more than 100 years. Gold or platinum toned prints probably have a lifespan limited only by the lifespan of the base material, probably many hundreds of years.[citation needed]
The archival potential of digital photographs is less well understood since digital media have existed for only the last 50 years. There exist three problems which must be overcome for archival usage: physical stability of the recording medium, future readability of the storage medium and future readability of the file formats used for storage.
Many digital media are not capable of storing data for prolonged periods of time. For example, 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.[citation needed]
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 5¼-inch Floppy disks were first made available in 1976. However, the drives to read them are already extremely rare just 30 years later.[14]
It must also be considered whether there still exists software which can decode the data. For example, many modern digital cameras save photographs in JPEG format. This format has existed for only around 15 years. Whether it will still be readable in a century is unknown, although the huge number of JPEG files currently being produced will surely influence this issue.[14]
Most professional cameras can save in a RAW image format, the future of which is much more uncertain. 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 simple 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.[15]
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.[citation needed]
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.[citation needed]
And, of course, the digital images can always be printed out and saved like traditional photographs although there are few , if any, commercial services available producing true silver halide prints from digital sources. All dye based prints, as noted above, have only limited permanence (with the exception of Cibachrome).[citation needed]
[edit] Integrity
Film produces a first generation image, which contains only the information admitted through the aperture of the camera. Film "sees" in color, in a specific spectral band such as orthochromatic, or in broad panchromatic sensitivity. Differences in development technique can produce subtle changes in the finished negative or positive, but once this process is complete it is considered permanent.[citation needed]
Film images are very difficult to fabricate, thus in law enforcement and in cases where the authenticity of an image is important (passport or visa photographs), film provides greater security over digital, which has the disadvantage that photographs can be conveniently moved to a personal computer for modification.[citation needed]
Nikon
film scanner, right, which converts 35mm film images to digital
[edit] Converting film to digital
Film photographs may be digitized in a process known as scanning. They may then be manipulated as digital photographs.
There are currently three ways to scan or convert a film image to digital format.[citation needed] The first is through a reflective image scanner. Inexpensive flatbed scanners, depending upon the model used, can scan a paper-sized image from 8" x 14" to ledger size, 11" x 17". 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. One can mount a digital camera on a copy stand (or an old enlarger with its projection head removed) and photograph 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.
[edit] References
- ^ Resolution Test Area 2: trees and Mountains R. N. Clark, 8 April 2001. Retrieved 2 September 2006.
- ^ Montclair Photo Resolution Guide
- ^ Why do Images Look Crappy Played on a TV
- ^ Canon EOS 5D Review: 22. Photographic tests:
- ^ Canon EOS 30D Review: 21. Photographic tests:
- ^ Canon EOS 40D Review: 20. Photographic tests:
- ^ Nikon D40 Review: 18. Photographic tests:
- ^ Nikon D40X Review: 18. Photographic tests:
- ^ Nikon D80 Review: 19. Photographic tests:
- ^ Nikon D200 Review: 22. Photographic tests:
- ^ Sony Alpha DSLR-A700 Review: 20. Photographic tests:
- ^ Fujifilm S5 Pro Review: 18. Photographic tests:
- ^ a b Bob Atkins. Size Matters. Photo.Net Equipment Article, 2003.
- ^ a b Stewart Brand. Escaping the Digital Dark Age. Library Journal vol. 124. Issue 2, pp. 46-49, June 20, 2003.
- ^ Dean M. Chriss. RAW Facts: The short life of today's RAW files: Demystifying the Debacle. DMCPhoto online article, April 29, 2005.
