Digital Resolution

RESOLUTION IN DIGITAL CAMERAS


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.

There are many measures which 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. This is measured by how many picture cells make up the photo, usually counted in the millions and hence called "megapixels".

Similarly, digital cameras rarely perform to their stated megapixel count. 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.

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 is used or less resolution to be recorded with poor quality optics or low light levels. The analysis of R. N. Clark leads to this conclusion: "The digital megapixel equivalent of film is highly variable and roughly depends on film speed. Slow, fine-grained 35 mm films with speeds of ISO 50 to 100 have estimated megapixel equivalents of 8 to 16 megapixels. ISO 400 films are only around 4 megapixels." This would place top-of-the-range digital cameras (as of 2006) well over 35 mm film cameras. However, different films with the same ISO speeds can have different lines, so a direct comparison to digital is not possible.

While 35 mm is the standard format for consumer cameras, many professional film cameras use Medium format or Large format 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.

The resolution of modern black and white slow speed film, exposed through a high quality prime lens working at its optimum aperture yields usable detail at a scanned file size of greater than 30 megapixels. With consumer 35 mm color negative film an effective resolution of over 12 megapixels is achievable and in an inexpensive 35 mm point and shoot camera a resolution of over 8 megapixels may be achieved.

When deciding between film and digital and between different types of camera, 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 2 megapixels and 1.3 megapixels, respectively, as of 2006), 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. Even if the print is to be large billboard, it is not clear that the extra resolution of a medium or large format will be necessary, since they are viewed from relatively long distances. For larger prints, the extra resolution of a good 35 mm film photograph may be desirable.