Evaluating and Measuring Color

• Printed color can be compared with the original either by eye or by color measuring instruments.

• The human eye is a very good judge of color as long as it is not deceived by variations in lighting conditions. Comparisons between two colors should always be made on identical backgrounds and under identical lighting conditions.

• The differences between colors can be described by referring to appropriate device independent color models. (e.g. CIELAB, HSL etc.)

• Changing hues of spot colors can only be done by remixing the inks.

• Changing the hues of process colors involves changes in the color separations.

• When precise specifications of colors are necessary, instruments must be used.

• A densitometer measures the amount of light reflected from a surface or transmitted through a film. To evaluate colors and color balance a set of color filters are employed in the densitometer.

• A Colorimeter is based on the RGB cone responses of the eye. Using measurements through a set of R, G and B filters, the instrument produces CIE tristimulus or chromaticity values.

• A Spectrophotometer measures the full reflectance spectrum of a color sample. These are converted to various CIE coordinates.

Color Difference

• The difference between two colors can only be quantified by reference to measured value.

• Quantifying color difference values is standard method used in quality control.

• For printed colors, it is conventional to report differences between the values of L*, a* and b* for the target and the sample.