light, colour & photography

where is middle grey?

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

you might also be interested in these articles: the dimension of light & dark | what is a grey card?

Nothing will ever reflect back 100% of the light that falls on it. Equally, nothing will absorb 100% of the incident light. There is no such thing as a perfect white or a perfect black. The best that can be achieved is approximately 90% reflectivity for the whitest white and about 5% reflectivity for the blackest black.

In practice a reference white comprises a ceramic tile, specially manufactured and calibrated with a known reflectivity.

The blackest black is achieved by having a small hole in a box lined with black velvet - far darker than a black paint or surface.

The greys occupy the intervening 85%:

Fig 1: linear grey scale

The question is: where is middle grey?

The grey scale shown above is a mathematically linear one combining a mixture of pure white and pure black. if you study the scale carefully you will probably agree that most of the greys appear to be situated towards the left hand side; those on the right seem not only to be paler but more spread out. This is a completely subjective impression. In the next diagram I have highlighted the area where I think most of the greys appear to be (you can click the image to reveal the area):

Fig 2: linear grey scale showing concentration of grey tones

The next diagram shows the same scale of greys but with a ruler measurement along the lower edge. Look at the diagram and check the measurement where you think "middle grey" is situated; that is a grey that is neither shifted towards the black nor the whites but appears to be perceptually mid-way between the two (you can hover the cursor over the image to reveal the scale then click it to reveal the area):

Fig 3: linear grey scale showing mid-grey

Most people choose a point on the scale around 160. So far so good. Or is it? Here is the same scale again but with a white background:

Fig 4: linear grey scale with scale

Did you think that middle grey was at the same point on the ruler?

Finally, here the other extreme; the same diagram against a black background:

how about gray chips and finding middle grey by eye? mid-way between white and black. Measure its reflectance - it will be about 18%

Fig 5: opposing linear grey scales

The further discussion of the neutral point can be found here <insert link> and the discussion of colour temperature can be found towards the end of this page. <insert appropriate links and references>

how about gray chips and finding middle grey by eye? mid-way between white and black. Measure its reflectance - it will be about 18%.

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