Film vs Digital: the big debate. You trust more human eye or pixel?
Dcinema is cheaper and faster so directors can shoot much more and take decisions in the least amount of time
But what is the film look? It’s something organic: the dynamic range of film, the depth of the blacks, the detail captured in the highlights.. when film is perfectly exposed it really is incredible how much detail and how much depth there is to the colour. On the flipside, if it’s badly exposed it can look terrible! But when you see something that’s shot on film and it’s well treated it’s a much nicer image, it has a greater effect on your emotions and the physical grain that is within film: it feels like it’s breathing, it feels like it’s alive.
When you record in Log mode, remember that you are attempting to match some of the qualities that are taken for granted in the world of film acquisition, namely 14+ Stops of dynamic range. The maths that allows sensors to mimic the response curve of silver halide. it’s the flaws and foibles of organic film stock that digital can’t do. It’s the imperfections of film they are passionate about preserving, the je ne sais quoi film look.
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Each photosite on a CCD or CMOS chip is composed of a light-sensitive area made of crystal silicon in a photodiode which absorbs photons and releases electrons through the photoelectric effect. The electrons are stored in a well as an electrical charge that is accumulated over the length of the exposure. The charge that is generated is proportional to the number of photons that hit the sensor. This electric charge is then transferred and converted to an analog voltage that is amplified and then sent to an Analog to Digital Converter where it is digitized (turned into a number). The number of electrons that a well can accumulate also determines the sensor’s dynamic range, the range of brightness from black to white where the camera can capture detail in both the faint and bright areas in the scene. Once noise is factored in, a sensor with a larger full-well capacity usually has a larger dynamic range. A sensor with lower noise helps improve the dynamic range and improves detail in weakly illuminated areas.
Although the digital camera can record 12 bits or 4096 steps of brightness information, almost all output devices can only display 8 bits or 256 steps per color channel. The original 12-bit (212 = 4096) input data must be converted to 8-bits (28 = 256) for output.
Due to the way our visual system works, if we divide the continuous tones into a sufficient number of small discrete steps we can fool the eye into thinking it is continuous tone even though it is not.
Linear vs Non-Linear Data
The recording response of a digital sensor is proportional to the number of photons that hit it. The response is linear. Unlike film, digital sensors record twice the signal when twice the number of photons hit it. Digital sensors also do not suffer from reciprocity failure like most films.
Human visual perception of brightness is more similar to a logarithmic curve than a linear curve. Other human senses, such as hearing, and even taste, are also logarithmic. This means that we are better at sensing differences at the low end of the perceptual scale than we are at the high end. For example, we can very easily tell the difference between a one-pound weight and a two-pound weight when we pick them up. But we have a great amount of difficulty telling the difference between a 100-pound weight and a 101-pound weight. Yet the difference is the same, one pound.
This is why it is important to work in a high-bit depth when working with raw images. Because of the strong stretches and increases in contrast that are necessary, tones are pulled apart. If we have a lot of tones, which a high-bit depth allows, they will re-distribute smoothly. If we do not have a lot of tones to work with, we run the risk of posterization and banding when we stretch the data.
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