Endocrine Abstracts (2012) 28 SE1.1

Seeing the light

Brian Cooke

2 Prospect Lane, Harpenden, United Kingdom.

The human eye is an incredible organ. It can differentiate contrasts of light up to 1:10,000, equivalent to a photographic exposure value (EV) range of 14. The eye can also adapt to any lighting situation, stretching the total perceivable range to 1:1 million. For many applications, we rely on the camera for recording what our eyes can see. But is the camera able to reproduce the full range of light intensities present in natural scenes? The human eye has two types of photoreceptor cells: rods and cones. Cones function in bright light and are responsible for colour vision whereas rods function in dim light but do not perceive colour. Colour vision is mediated by three receptors - red, green and blue absorbing. In the digital camera the equivalent of the retina is the sensor which is made up of millions of light sensitive cells. Each cell has its own filter; either red, green or blue. The amount of data recorded on the memory card of a digital camera is determined mainly by the file format used, the most common one being JPEG. However the use of this format results in the discard of data resulting in a low EV of 7–8. The RAW format does not discard information and can achieve 9–10 EVs. High Dynamic Range (HDR) photography enables the recording of a greater range of tonal detail. This is achieved by combining a series of bracketed exposures into a single image. This encompasses the tonal detail of all the exposures and can achieve EVs equal to the tonal range of the human eye. These different approaches to emulating the human eye will be compared and examples of the images obtained will be shown.

Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.

Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.

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