Digital versus film photography has been debated since the 20th century when digital cameras were invented. 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.
Image quality
Spatial resolution
The quality of digital photographs an 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 resolution and 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 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, less resolution may be recorded with poor quality optics or with coarse-grained film. A 36 mm x 24 mm frame of ISO 100-speed film is estimated to contain the equivalent of 20 million pixels.
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, which is similar to medium format film quality.
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 a television or computer display, which can resolve approximately .3 megapixels and 1-2 megapixels, respectively, or HDTV sets of 1080p that can display 2MP, the resolution provided by inexpensive digital cameras may be sufficient.
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 noise than those made at lower sensitivities.
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.
Dynamic range
Dynamic range(DR) is a complex issue. Comparisons between film and digital media should consider:
- Film type: For example, low-contrast print film has greater DR than slide film's low DR 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 sensor sites 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 DR 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 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 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 DR."
The digital camera industry is attempting to address the problem of dynamic range. Some CCDs like Fujifilm's Super CCD combines 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 .
Effects of sensor size
Almost all compact digital cameras, and most digital SLRs, have sensors 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.
Depth of field at a given f-numberincreases as the area of film or image sensor decreases. This may have advantages for compact digital cameras 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. 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. Depth of field can be minimized by use of large format cameras, which are 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 increase, the size of the individual pixels 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.
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 affect the image resolution because of increased noise reduction.
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. Debris in the camera, such as dust or sand, may scratch the film; a single grain of sa
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