Film vs. Digital Sensor

In film photography, the image is created by exposing onto silver halide coated film. Silver halides are used in photographic film and paper, where silver halide crystals in gelatin are coated on to a film base, glass or paper substrate. In digital photography, this coated film is replaced with either one of 2 types of digital sensors. The earlier charge-coupled device sensor, also known as the CCD sensor. And the newer, quickly growing and stealing the spotlight, the complementary metal-oxide semiconductor, also known as the CMOS image sensor.

The digital sensor serves the same purpose in digital photography, as does film in film or analogue photography. They both represent the medium light is gathered onto to expose an image.

Superficially, Key features in film and digital cameras are very similar. The truth is, however, that digital cameras have a whole new level of camera software and settings complexity.

Both, the digital image sensor and film are based on the key element Silicon. When mixed with other elements, Silicon becomes sensitive to light. In digital photography, when light-sensitive Silicon is exposed to light, this light is gathered, converted, and saved as a stream of 1s and 0s onto the digital memory storage media.

One of the main differences between digital and film imaging is that, light gathered on film is permanently stored there and that space is neither reusable nor editable. Whereas light gathered onto the digital sensor is actually processed and sent off to storage on a whole different medium, the camera’s memory card. If this processed instance of exposure is stored onto the digital medium without compression or manipulation, this data is indeed retrievable, and editable, without degradation of quality to some extent.

Another, very fundamental difference is, that the digital image is captured on a grid of light sensitive pixels, and each of these pixels produces an image result depending on the amount of light hitting it. Where in film, light-sensitive elements are randomly distributed along the film emulsion, overlapping to create a sense of continuous color tone gradation. Pixels on the other hand are not overlapping, so when an image is enlarged beyond a significant extent, these pixels become more and more visible. Furthermore, pixels can only represent certain color values as solid blocks. This means that one pixel can only represent one color value even though the light and color information falling on it from the original scene can contain multiple values. And this is why digital photography is known to produce a non-continuous, incomplete gradation of color tones, an area in which film photography is still ahead of the whole new digital trend.

The following figure represents a “hypothetical” mockup of a grayscale gradation of a scene, and how it might be represented on a digital medium. Of course it all depends on the bit-depth of the stored file. i.e. a 16-bit image stores much more color info than does an 8-bit image, meaning the gradation of a grayscale for example in a 16-bit image, is much more homogenous and continuous than that in an 8-bit grayscale image.

For those of you out there who are not familiar with the term “Bit-Depth”, Color depth or bit depth, as Wikipedia defines it, is a digital graphics term describing the number of bits used to represent the color of a single pixel in a bitmapped image or video frame buffer. This concept is also known as bits per pixel (bpp), particularly when specified along with the number of bits used. Higher color depth gives a broader range of distinct colors.

So in short, in 8-bit mode you have 256 levels or color shades per channel (red, green, blue). Whereas in 16-bit mode, you have over 65,000 levels or color shades in each of those channels.

This stepped (non-graduated) quality of color tone changes is a huge barrier in terms of image quality and resolution, and is directly impacted by the sensor sensitivity to light, the analogue to digital conversion capabilities of the camera, and the output file format. And a key role why film photography still has a huge fan base of its own.