CD40154 Version 2.1 6
2 About color measurement
2.1 Multi-channel camera vs. true color measurement
If one is used to do ‘simple’ inspection using gray scale or RGB cameras, truePIXA is the
consequent extension from RGB (3 channel) to a 12 channel system, whereas the channels of
the system are optimized to cover the visible spectral range. Applications where the three RGB
channels are not sufficient (e.g. color separation in general terms), can be treated with
truePIXA. Within the application truePIXA offers the extension of color image processing from
three to twelve channels. In this case system stabilization and especially the design of the
illumination does not differ compared to any imaging system used for inspection.
On the other hand, if the system is used for high quality color control, every component must be
well defined, controlled and especially stabilized to guarantee the short term, long term and
absolute color precision of the measurement system. Any measurement cannot provide higher
precision and quality as the general setup provides. The weakest point within the design will
always limit the general performance. Therefore no technical point of the whole system can be
thought as insignificant, unless it is proven explicitly.
2.2 Point measurement spectrometer vs. true color imaging
Standard color measurement devices used in industry are point measurement instruments.
Typically the sample’s surface is illuminated circular under 45° [ISO 13655]. The diffuse
remission of the surface is measured at 0°, and spectrally resolved using a diffraction grating.
The diameter of the aperture is typically about 2.5mm – 4mm. One measurement lasts roughly
1 second. That corresponds to a measured area of 5-12 mm² per second. A typical
configuration of truePIXA operates up to transport speeds of 5.5m per second with a scanning
width of 250mm. That corresponds to a measured surface of 1 375 000 mm² per second.
That simple calculation is made to give an impression about the strength, and great advantage
of truePIXA. Additionally the system provides a freely tunable ROI size, shape and position.
The latest standard devices for color measurement are handheld devices. We compare the
absolute (color-) agreement of truePIXA with those standard devices.
The typical performance in an optimal system is:
•Mean dE
76
= 1.2 (measured on 100 HKS-samples)
•Short term repeatability = 0.04 dE
76
(mean value 10 measurements on white)
