Digital Cameras vs. Film

Despite the massive strides it has made in recent years, the conventional wisdom remains that though digital cameras offer advantages in term of flexibility, when it comes to picture quality they still fall a significant way behind that of a traditional camera and film. However, since this assertion involves the comparison of two radically different technologies, it is worth considering more closely.

The first step is to consider resolution. Whilst its easy to state the resolution of a digital camera’s CCD, expressing the resolution of traditional film in absolute terms is more difficult. Assuming a capture resolution of 1280×960 pixels, a typical 1999 model digital camera is capable of producing a frame size of just over 1.2 million pixels. A modern top-of-the-range camera lens is capable of resolving at least 200 pixels per mm. Since a standard 100ASA 35mm negative is 24x36mm, this gives an effective resolution of 24x200x36x200 = 34,560,000. This resolution is rarely achieved in practice and, indeed, rarely required. However, on the basis of resolution, it is clear that digital cameras still have some way to go before they reach the level of performance as their conventional film camera counterparts.

However, this is only part of the answer. The next factor to consider is colour – and here digital cameras have an advantage. Typically, the CCDs in digital cameras capture colour information in 24 bits per pixel. This equates to 16.7 million colours and is generally considered as being the maximum number the human eye can perceive. On its own this doesn’t constitute a major advantage over film. However, unlike the silver halide crystals in a film, a CCD captures each of the three component colours (red, green and blue) with no bias. Photographic film tends to have a specific colour bias – dependent on the type of film and, to a certain extent, the manufacturer – and this can have an adverse effect on an image, according to its colour balance.

However, its also its silver halide crystals that give photographic film its key advantage. While the cells on a CCD are laid out in rows and columns, the crystals on a film are, to all intent and purposes, randomly arranged with no discernible pattern. As the human eye is very sensitive to patterns, it tends to perceive the regimented arrangement of the pixels captured by a CCD very easily, particularly when adjacent pixels have markedly different tonal values. Magnify photographic film, and though the dots will be discernible, there will be no apparent regularity. Its for this reason that modern inkjet printers use a technique known as stochastic dithering, which adds a random element to the pattern of the ink dots in order to smooth the transition from one tone to the next. Photographic film does this naturally, so the eye perceives the results as less blocky when compared to digital stills.

There are two possible ways around this problem for digital cameras. Manufacturers can either develop and build models that can capture a higher resolution than the eye can perceive, or they can build in dithering algorithms that alter an image after it has been captured by the CCD. Both of these options have downsides however, such as increased file sizes and longer processing times.