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in Reply to Vol 2, Issue 3: 3. Colorimeter vs. Spectro In answer to previous postings, this posting is intended to provide a clear understanding of the differences between filter based spectrometers, diffraction grating based spectrometers and colorimeters. When obtaining color measurements from a monitor, a filter based spectrometer with 20nm (like Pulse) or even 10nm resolution, can't capture enough precise spectral details of the light emitted by monitors. However, diffraction grating based spectros (like Eye-One) feature a 3.5nm physical sampling interval, providing more than 100 channels compared to 15 channels from a 20nm filter device with no over sampling. The 100 channels overlap due to 10nm optical bandwidth of the spectral module. Therefore, grating based devices don't miss any critical information and are able to resolve the wavelength of a laser line (the sharpest edge possible) ultimately resulting in a resolution far more precise than 1 nm! This is why colorimetric results calculated with Eye-One's spectras measured on a monitor agree very precisely with those calculated from spectrometers featuring an optical resolution of 1nm! A filter based spectrometer will not capture all the critical data and, therefore, does not support measurements on monitors, which is why a user of such a device must choose to use a colorimeter or a diffraction grating based spectro for monitor measurement. GMB spectral devices are stable over time and feature an excellent inter-instrument agreement which is independent of the measured spectrum. This is due to the fact that the filter characteristics required to obtain the colorimetric results are set in software and do not depend on optical characteristics of filters (like colorimeters) which change from lot to lot and also change over time. The lot-to-lot differences of these filters can be compensated to a certain extent for a given spectral distribution during calibration at the manufacturing site. However, this is at the cost of introducing errors when the spectral distribution of the monitor is different from the one assumed during calibration. Advantages of diffraction grating based spectros: 1) 10nm/3.5nm grating based spectrometers like the Eye-One perform better than colorimeters when monitors with different spectral characteristics must be matched. 2) The consistency of the measurement results is better when the same measurement device can be used for reflectance and emission measurement (like with the Eye-One or Spectrolino) because both colors are measured with the same resolution of more than 100 channels, plus there are no inter-instrument agreement errors brought into play. 3) The inter-instrument agreement of 10nm/3.5nm grating based spectrometers (like the Eye-One) don't depend on lot-to-lot changes of optical filter characteristics. Colorimeter clarifications: Marc Levine wrote>>Incidentally, it is my impression that Colorimeter filters are engineered to match the human eye response and not the spectral character of the device which they are measuring The opposite is true. Manufacturing colorimeters using filters to match the precise response of the human eye is not advisable. First, it is simply too expensive to build filters which feature (in combination with the applied photodiodes) the complex shape of the colorimetric weighting functions or a linear combination thereof. Secondly, due to several technical reasons that would go beyond the scope of this message, manufacturers choose different filter curves in their colorimeter design. Nevertheless colorimeters are still able to provide good results although the sensitivity curves do not match the human eye response as precisely as a grating based spectrometer. A grating based spectrometer measures monitors more precisely than a colorimeter because it features over 100 channels capturing all the detail information of a monitors spectral characteristic and the filter curves are implemented by software and not by physical filters like in a colorimeter. Therefore, if you have an i1 spectrometer you don't need a colorimeter to measure monitors. However, if you wan't to measure monitors only, a colorimeter does a good job at an affordable price. If you plan to buy a more expensive spectrometer for measurement of reflective targets and you chose a filter based product that can not measure monitors like pulse, you may reconsider your decision, because an i1 delivers higher resolution results on paper and monitors. Conclusion: filters of colorimeters are designed to deliver best performance on the devices they are designed for - monitors. Filter based spectros provide good performance for reflective measurement but are not conducive for emissive measurement. Diffraction grating based spectros feature precise color matching functions implemented numerically and independent of the measured device and provide the superior choice for measuring both emissive and reflective. Andreas Brant GretagMacbeth Corporate Support e-mail: email@hidden www.gretagmacbeth.com _______________________________________________ Do not post admin requests to the list. They will be ignored. Colorsync-users mailing list (email@hidden) Help/Unsubscribe/Update your Subscription: This email sent to email@hidden
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