light, colour & photography

what is a grey card?

you might want to read the previous article: what's special about grey?

you might also be interested in these articles: where is middle grey? | exposure value

Before reading this article you should be familiar with the article entitled "what's special about grey?". That article lays the foundations for two unique properties of grey:

1. it reflects back a fixed proportion of the incident light
2. it does so without changing the colour of the incident light

Without these two basic concepts there is absolutley no point in reading further.

The property of being neutral gives to the grey card one important attribute. The grey card will reflect back exactly the same colour of light that falls on it, albeit less of it. For this reason alone the grey card can be used in assessing the "white point" (or, more strictly, the "neutral point"; in German the description is even more exact: the "unbuntpunkt" - the uncoloured point). But why would we want to undertake this kind of assessment?The answer is colour temperature or, more strictly, the extent to which the ambient illumination departs from the neutral point.

intro

grey card

18% Grey Card for γ=1.8

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	Pop-up version of the document (100%). Right-click to download and save. The RGB values for this sample are: R: 105 G: 105 B: 105 This is equivalent to #696969 with a lightness value (HSL) of 105

18% and 12% grey cards

additional description goes in here