Can you and I agree on colour?
Do you and I see the same colour when we look at a red object? We may be seeing completely different hues, or tones. There is no way to objectify colour. We see it, have have name for it, but we cannot agree that we see exactly the same thing. What we see is an internal experience and we cannot share it with other people.
When we see a photograph taken under the influence of a tungsten or fluorescent light we can clearly see the colour casts. Modern DSLRs have standard white balance settings to neutralise these colours as they are so common. What about colour casts that are not so common? Well, in that case we need to set up a custom white balance setting.
The problem is, we do not have an objective measurement of colour that means the same to everyone. However, if we can standardise colour against something, then we would have a way of sharing a colour on a fixed basis. You may see a slightly or very different colour to me. But when you do, if it is standardised, it does not matter. That’s because we can both agree on it against the same standard.
Light which may appear white to the eye is not necessarily an even distribution of colours. The visible colour spectrum contains a combination of colours which together form white. The various colour temperatures in that mix are manifest at the different colour wavelengths. In photography we use a neutral grey (18% grey) as a calibration point that represents the 50% point in the eyes’ contrast range between brilliant white and perfect black. We can use this grey level to allows us to neutralise colour casts generated by sources which are not on the white light spectrum.
How do we neutralise these colour casts using 18% grey? Well, if certain scenes are slightly off colour or we are unable to create a clean white in a white environment there is probably a colour cast or the camera is compensating for too much brightness. For example, it’s common to have grey snow if the camera overcompensates for brightness in the whites. If we calibrate the camera for a custom white balance we can set white settings to be true to the scene in which the grey card is used. To establish the calibration point we photograph the 18% grey card within the light that contains the colour cast. Then we set the 18% grey point to be correctly grey (18%) and this will even out the colour cast. Check your manual for the exact procedure for your camera model.
Of course this assumes that the manufactures got the colour range-calibration correct. However, there is good evidence that we all agree the calibration points produce consistent colour results. So, if we calibrate the camera to the 18% grey card in the ambient light (with colour cast) the same camera colour range will shift from the colour cast to make the camera see the card as 18% grey again. The adjusted colour is a custom white balance – but it adjusts the colours to be consistent with the grey card standard.
Is Your Red The Same as My Red?
In the video we see that it is difficult to agree on the colour match between people. The video shows how different people can see a colour in a unique way but still agree on the existence of the colour even though our experience of it can differ. However, in reality we can only behave as if we agree that colours are the same. We do not have actual knowledge they are same to everyone. Hmmm! Mind bending… but worth thinking about
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