By Elite Screens marketing manager Dave Rodgers.
I really had to fight off the peer pressure of my associates in the AV world to avoid toning down the complexity of this subject but it needs to be put into more layman-friendly terms. This is important because while this is common knowledge to an installer, the average customer has no idea about this stuff. This topic has been covered in all its glorious intricacy by best minds in organizations like SMPTE, CTA, InfoComm, ISF and CEDIA. However, I recommend a more basic approach to someone who doesn’t know lux from lumens.
To understand black-white levels and contrast, here are three characteristics of any perceived colour that you should know.
- Colour Saturation: This is the intensity of a colour. Think of a glass cup full of red paint and how it gets lighter with every drop of water you use to dilute it. The colour is lighter because the colour saturation is lower. The colour is fuller when colour saturation is higher.
- Hue: This represents the full range of colours that can be seen. This incorporates the full Red, Orange, Yellow, Green, Blue, Indigo, and Violet colour spectrum.
- Luminance: The measured presence from the black-white dynamic range that occurs with a measured point of colour. It determines the brightness or darkness of an image. This is broken down to Tint (adding white to the colour) and Shade (adding black to the colour).
There is often confusion between the definition between the word ‘Contrast’ and ‘Black-White Dynamic Range’ (aka. Black Levels – See fig. 1). While contrast can describe how lighter and darker portions of an image differentiate from one another, that’s only part of the story. Although black-level dynamic range can enhance contrast, the same can be said about varying levels of colour saturation whereas a more deeply saturated colour will contrast with a lesser saturated colour in the same spectrum. (See fig. 2.)
Dynamic Range incorporates the points of measurement between the purest white and the deepest black that you can achieve with the equipment you have. Interestingly, this is the most important element of picture calibration because the human eye sees detail in black and white.
Colour perception is merely a further visual enhancement but without dynamic range, it is impossible for your eyes to see the various textures and details in imagery occurring at either the lighter or darker ends of this particular spectrum. This is also frequently referred to as ‘Black Levels’.
Keep in mind that true black is not an actual colour but the mere absence of any light in the spectrum. For this reason, a video image can never be truly black; it can only present a minimal presence in colour.
The human brain interprets all its perceived colour signals in Red, Green, and Blue or RGB. It is from these three colours that the human brain interprets the various hues or red, orange, yellow, green, blue, indigo and violet (ROYGBIV) based on the varying levels of RGB present to create any given colour.
In summary while it’s easy to tell different colours apart from one another, there is more to the story about contrast than just black and white. The intensity of colour matters just as much.
Dave Rodgers is Elite Screens marketing manager and has 20 years experience in the AV and wireless communications industries. He has made numerous television, radio and editorial appearances providing installers and do-it-yourselfers with easy solutions toward creating larger-than-life big screen applications.
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