Dotmeter vs Densitometer
Dotmeter vs Densitometer
To those new to this discussion let me offer the following clarification;
A dotmeter is an image analysis device used to determine effective halftone dot area and provide a magnified image of the sample. On more capable models screen ruling, screen angle, and dot diameter are also calculated and displayed. Conventional (AM) screening and stochastic (FM) screening can be measured on many instruments. Continuous tone and color density is not measured with these devices.
Because dotmeters determine the actual dot size and geometry, their measurements are called "mechanical dot area" and will be in excellent agreement with any TIFF reader values. Differences between the TIFF value and the plate are due to the exposure and processing and are an accurate method to verify the stability of the process. They do not need any mathematical adjustment or 'n' factor. The UltraDottie II series from Beta Industries is offered in different configurations to satisfy the requirements of any workflow. Details can be seen here:
Beta Ultra Dottie 2
Densitometers don't "know" or care what they are measuring, only offering information about the average reflectance of the sample. Spectral data or colorimetric data provides no greater accuracy or benefit over simple density data. The measured value is NOT the same as the true mechanical dot area and will not be in agreement with the TIFF value. Any densitometer that is stable and repeatable will tell you when the reflectance of the plate has changed but the reading will not be the true dot area.
Densitometer illumination systems have to be carefully designed to avoid sensitivity to directional effects in the aluminum substrate. If different results are reported depending upon the orientation of the instrument, then another complication has to be dealt with by the operator. The best illumination system for plate densitometers uses 360 degree illumination to eliminate directional sensitivity. The Platemaster from Beta Industries offered such an illumination arrangement. Now discontinued, it is supplanted by the UltraDottie II line.
All dotmeters and densitometers need a visible image of suitable contrast to produce accurate measurements. If you cannot see the image you cannot measure it. Various techniques to stain the image, manually develop it, or otherwise increase the contrast may be required. Dotmeters are available with multi-colored light sources to optimize the contrast of the image.
Dotmeters can also be supplied with traceable, absolute, dot area calibration standards. The Beta UltraDottie II, also sold as the X-Rite icPlate, comes with a chrome-on-glass target and a calibration database. ISO-registration management is greatly simplified, as well as superior inter-instrument agreement. Geographically distant plants can produce identical plates with solid data to back them up.
Larry Goldberg
Technical Director
Beta Industries
80-272-7336
Color Densitometers, CTP Calibration Systems for Print Quality
