Digital versus film photography

The merits of digital versus film photography were considered by photographers and filmmakers in the early 21st century after consumer digital cameras became widely available. Digital photography and digital cinematography have both advantages and disadvantages relative to still film and motion picture film photography. In the 21st century, photography came to be predominantly digital, but traditional photochemical methods continue to serve many users and applications. The merits of digital versus film photography were considered by photographers and filmmakers in the early 21st century after consumer digital cameras became widely available. Digital photography and digital cinematography have both advantages and disadvantages relative to still film and motion picture film photography. In the 21st century, photography came to be predominantly digital, but traditional photochemical methods continue to serve many users and applications. The visual quality of a digital photograph can be evaluated in several ways. The pixel count of an image is related to its spatial resolution and is often used as a figure of merit. The quantity of picture elements (pixels) in the image sensor is usually counted in millions and called 'megapixels'. Sensor pixel density sets a limit on the final output resolution of images captured with that sensor. Other factors, such as the effect of a Bayer pattern or other filter on the digital sensor and the image processing algorithm used to interpolate raw sensor data to image pixels. Most digital sensors are arranged in a rectangular grid pattern, making certain images (for example of parallel lines) susceptible to moiré pattern artifacts. Film is not affected by moiré because of the random orientation of the silver salts in its emulsion, however the pattern of these silver salts may become visible upon enlargement, creating the patterns called 'grain' in the final output. The resolution of film images depends upon the area of film used to record the image (35 mm, medium format or large format) and the film speed. Estimates of a photograph's resolution taken with a 35 mm film camera vary. More information may be recorded if a fine-grain film is used, while the use of poor-quality optics or coarse-grained film may yield lower image resolution. A 36 mm × 24 mm frame of ISO 100-speed film was initially estimated to contain the equivalent of 20 million pixels, or approximately 23,000 pixels per square mm. Many professional-quality film cameras use medium-format or large-format films. Because of the relatively large size of the imaging area these media provide, they can record higher resolution images than most consumer digital cameras. Based upon the above pixel density, a medium-format film image can record an equivalent resolution of approximately 83 million pixels in the case of a 60 x 60 mm frame, to 125 million pixels in the case of a 60 x 90 mm frame. In the case of large format, 4 x 5 inch films can record approximately 298.7 million pixels, and 1,200 million pixels in the case of 8 x 10 inch film. However, as with a digital system, poor optical quality of lenses will decrease the resolving potential of a film emulsion. Shot noise, produced by spontaneous fluctuations in detected photocurrents, degrades darker areas of electronic images with random variations of pixel color and brightness. 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, with digital cameras, images taken at higher sensitivity settings show more image noise than those taken 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 in digital cameras can produce color distortion or confetti-like patterns, in indoor lighting typically 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 noise due to pixel leakage. 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 marginal sensitivity of the film changes with lengthy exposures, a phenomenon known as reciprocity failure. Traditional exposure metering and autofocus systems employ secondary sensors, whose readings are typically low-fidelity (e.g. a very small number of averaged readings from various image areas vs. fully resolved image information) and may not correspond to the actually recorded image, for example due to parallax issues, differing sensitivity towards polarization, differing spectral response, differing amplitude response, optical aberrations of optical elements in the sensing system, differing sensitivity towards stray light, or misalignment of the focal plane of the sensor.Most digital cameras allow users to capture and analyze image information from the same sensor as used for image recording in real-time. Using this information for exposure and focus determination inherently eliminates most alignment and calibration issues, while simultaneously eliminating the cost of secondary metering sensors.