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The MBS Features
Objective assessment
Not operator sensitive
Repeatable
Excellent correlation with visual perception
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Calender Blackening is a phenomenon caused by local increase of transparency of paper, resulting from a local reduction of light-scattering. These areas, which appear dark to reflected light, are areas of highest translucence. The ink on printed papers shines through the transparent areas and increase the effect of calender blackening. Such sheets look grayish or dirty and cause complaints by printers.
The visual assessment of calender blackening is a highly subjective process making it difficult for mills and printers to agree on a common specification. With the
emco Calender Blackening Analyzer (System Dr. Praast)
the papermaker has a reliable and repeatable tool to objectively assess calender blackening.
The emco Calender Blackening Analyzer (System Dr. Praast) uses reflected light, black backing of the samples and a CCD camera (512*512 pixels, 256 gray values). To achieve good correlation with visual perception a combination of first and second order statistics is applied to the images to take into account the contrast and size of the blackening pattern.
By adding the Missing Dots Module the MBS can be expanded to measure the number of missing dots per unit area on halftone prints. |
