Colour Measurement

Abstract

As was recently noted in NATURE¹, an increasingly high degree of accuracy in the specification of colour in terms of C.I.E. units is now being sought as a result of the growing realization of the indefiniteness of the colour discrimination limen and the low values it can assume in quite ordinary conditions. One would normally regard such circumstances as indicating in any physical quantity to be measured an ultimate need for correspondingly higher absolute accuracy, but it should not be overlooked in this case that higher discrimination is really called for in a quantity different from the one already standardized for use in colorimetry. The latter quantity, which is defined by the C.I.E. (1931) resolutions and data and will be denoted generally below by xO.I.E., refers to (a) a normal observer and (b) normal observing conditions, including particularly (c) a field of direct observation of 2° to which observations were necessarily intended to be restricted in order that they should apply to a region of uniform retinal structure and thereby have analytical significance.