Application and Optimisation of the Spatial Phase Shifting ...

128 Comparison of noise in phase maps from TPS and SPS
5.5.4 Direct comparison of the in-plane geometries
To summarise the findings from the in-plane experiments in a useful form, we shall re-consider them in a
direct confrontation; this is done in Fig. 5.14 with some selected N y for each set-up. The TPS mixedsensitivity
configuration does not appear here since the pure in-plane configuration outperforms it clearly;
the σ d,max for the pure in-plane set-ups are still at 0.20λ, which is indicated by the dashed white grid line.
0.35
σ d /λ
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0 0 0
20 20 20
50 50 50
100 100 100
0 2 4 6 8
d s /d p 10
N y
Fig. 5.14: Confrontation of σ d for the different in-plane measurements. SPS mixed-sensitivity set-up: all black;
pure in-plane symmetrical set-up for TPS: all white, bold lines; and for SPS: black bold lines, white filled
symbols. The selected N y are indicated in the legend box.
For N y =0, the σ d for both of the SPS methods are very similar. With increasing displacement, the pure inplane
configuration gains an advantage thanks to its high sensitivity, but also because the field of view is
larger; the discussion given in 5.5.3 applies likewise here. But since the displacement data are output as
sawtooth images first, it is also important how co-operative a sawtooth image will be in unwrapping. To
understand this, Fig. 5.15 provides a visual demonstration of the best sawtooth images from each method
for N y =10 (which corresponds to 7.5 fringes/768 pixels, cf. Chapter 4.2).
Fig. 5.15: Visual comparison of sawtooth images with N y =10 from the various pure in-plane set-ups. Left: TPS
pure in-plane, d s =1.5 d p ; centre: SPS mixed-sensitivity, d s =3 d p ; right: SPS pure in-plane, d s =6 d p .