Prakt. Met. Sonderband 38 (2006) 111 
the high _ 
pre-processing pre-processing no pre-processing Porosity after 
procedure with high- | procedure with edge Archimedes 
. pass-filter enhancement _ 
|_100x | 13,340,3% 1 13,4+0,3% ! 13,940,3% _ 11,7% 
ı 200x 11,040,6% = 11,7£0,6% _ 11,6+0,6% ‚7% 
500x 9,4+1,2% 11,2+1,1% 10,1+1,0% ey, (90 
Table 3: Mean values and intervals of confidence (a=0,05; n=20) for porosity after quantification from 
images taken at different magnifications, maximised contrast and pre-processed after different routes 
From the results presented in Table 3 200x magnification and images without pre- 
processing or with edge enhancement were chosen for further examination on the 
materials with calculated porosities of 17,5% and 7,3%. From two samples of each 
porosity at 200x 10 images each were taken in bright field. The images were pre- 
processed and porosity quantified as described above. Quantification without use of the 
edge enhancement filter yielded a slightly low result at 7,3% porosity and a slightly high 
result at 17,5% porosity. The edge enhancement filter had to be optimized for each 
porosity value. By changing the p value in (4) from 0,50 to 0,45 the result for a porosity of 
7,3% could be improved from 6,7+0,4% to 7,2+0,3%. At a porosity of 17,5% a p value of 
0,55 led to a result of 17,4+0,5% compared to 17,7+0,5% with p=0,50. 
Measured porosity: Measured porosity: Measured porosity: Porosity after 
no pre-processing edge enhancement edge enhancement Archimedes 
ght colours with standard with optimised 
value (p=0,50 value 
7,0+0,3% i! 6,7+0,4% 7,2+0,3% (p=0,45 7,3% 
11,60,6% 11,7+0,6% 11,7£0,6% an Tare 
i 18,1+0,5% 17,7£0,5% 17,4+0,5% (p=0,55) 17,5% 
Table 4: Mean values and intervals of confidence (0=0,05; n=20) for porosity after quantification from 
images taken at 200x magnification, maximised contrast and pre-processed with the noise reduction filter 
and the edge enhancement filter (standard and optimised p value) 
By utilising equation (5) and the observed values for standard deviation the number of 
images necessary for a desired interval of confidence can be estimated. At 200x 
magnification, standard deviations in the range of 0,8 to 1,2% were observed. Table 5 
shows calculated intervals of confidence (a=0,05) for different standard deviations and 
numbers of images. Since the standard deviations calculated from the images are just 
estimations of the true standard deviation, the number of images should be chosen rather 
higher. For a confidence interval below +0,50%, 20 to 30 images should be used in 
quantification. 
Estimated values for standard deviation | 
Number of images ; 0,80% 1,00% 1,20% | 
10 +0,57% +0,72% +0,86% 
+0,37% +0,47% +0,56% 1 
Fo +0,30% 40,37% +0,45% | 
yundary of 40 1 40,26% +0,32% +0,38% 
Table 5: Intervals of confidence (a=0.05) for several values of standard deviation and number of images