**2.1 Imaging photometers and colourimeters**

Colourimetry is the measurement of the wavelength and the intensity of electromagnetic radiation in the visible region of the spectrum. Colourimetry can help find the concentration of substances, since the amount and colour of the light that is absorbed or transmitted depends on properties of the solution, including the concentration of particles in it. A colourimeter is an instrument that compares the amount of light getting through a solution with the amount that can get through a sample of pure solvent (Fig. 1.). A colourimeter contains a photocell is able to detect the amount of light which passes through the solution under investigation. The more light that hits the photocell, the higher the current it produces, hence showing the absorbance of light. A colourimeter takes 3 wideband (RGB) readings along the visible spectrum to obtain a rough estimate of a colour sample. Pigments absorb light at different wavelengths.

The use of imaging photometers and colourimeters for fast capture of photometric and colourimetric quantities with spatial resolution has attracted increasing interest. Compared with measuring instruments without spatial resolutions, such as spectrometers, this technology offers the following advantages:


However, the absolute measuring precision of imaging photometers and colourimeters is not as high as spectroradiometers. This is because of the operational principle using a CCD Sensor in combination with optical filters, which can only be adapted to the sensitivity of the human eye with limited precision.

Imaging photometers and colourimeters are the instruments of choice for:


Fig. 1. Minolta Cr 200 colourmeter (Beyaz, 2009a).
