STFI OptiTopo – a unique method to correlate surface topography and print defects
The STFI OptiTopo can help you reveal the interaction between surface topography and print quality in a unique way. Questions about how the surface topography is affected by different calendering, coating, base paper, or if there is a match between topography variations and print defects can be answered using the method.
STFI OptiTopo (Figure 1) provides additional information at different levels when compared to classical air-leak devices (e.g. PPS, Bendtsen). Acquisition and processing time are much faster than current mechanical stylus or laser instruments.
Figure 1. The STFI OptiTopo instrumentation
Two images of the same region of a paper sample are acquired, illuminated in a low angle from opposite directions, using a dedicated setup. The height map is calculated using a “photometric stereo” technique. Frequency analysis is applied on the height map to separate the small-, mid- and large scale variations and their respective contributions when predicting print quality. It is currently possible to measure areas from 6.5 mm x 6.5 mm up to 30 mm x 30 mm. Normally 8 areas are used for better statistics. Both printed and unprinted samples can be measured.
The result is the topography variation in different wavelength classes, and images, such as those shown in Figure 2.
Figure 2. Appearance of the surface (left). Height map colour-scaled in microns (centre). Combination of intensity image and valleys of a specified depth (right)
Innventia carries out analysis using STFI OptiTopo on a commission basis.