Statistical Analysis of Widths and Heights of Images from 

Segmentation Data 

July 15, 2008 

Jin Chu Wu 

In the draft of “Specifications for Fast Tenprint Capture Devices”, Version 1.0, it states that the 

evaluation of FTC devices is threefold: the absolute measurement stipulating the specifications 

and designing targets to implement specifications, the relative measurement for interoperability 

matching 2-d rolled-equivalent fingerprint images produced using FTC devices against those 

collected from certified live scanners, and the real-time speed of completing one transaction 

carried out by an FTC device. Further, the absolute measurement requires the evaluation 

regarding the geometric accuracy. Thus, a target that can simulate the human fingers needs to be 

designed. Now the question is what sizes these simulated fingers should be. 

In order to obtain the finger sizes, one way is to collect samples. For instance, the human finger 

sizes can be collected in any public areas. Then, an inferential statistical analysis follows. 

The alternative is to analyze the segmentation data. However, it must be noticed that 1) the sizes 

of two thumbs cannot be obtained, 2) only the widths and heights but not the thicknesses of the 

fingers can be estimated, 3) the widths and heights shown in the segmentation data are the widths 

and heights of images, respectively, that are smaller than the widths and heights of real fingers, 

which is because only the front part of a finger touches the platen of a live scanner to form a flat 

image during a capture process. This third point is the most important issue. Nonetheless, the 

analysis of the segmentation data can provide some information, for example, the proportion 

between two finger sizes, etc., for designing the simulated fingers to be the targets in the absolute 

measurement. 

The segmentation data provided by Craig Watson’s subgroup included data from dos3s and 

lacnty (LA County). Some data contained the age information, but some data didn’t. In addition, 

some data were corrupted, in which the sizes of width and/or height were inappropriately 

recorded, or the birth date and the capture date did not match properly, or the age of the subject 

was less than 10. The corrupted data were deleted. 

As a matter of fact, the set of the segmentation data is the direct product of the set of gender 

(male and female), the set of eight fingers (R2, R3, R4, R5, L7, L8, L9, and L10), and the set of 

the dimension (width and height). They can be mathematically expressed as, 

{segmentation data} = {male, female} ⊗ {R2, R3, R4, R5, L7, L8, L9, L10} ⊗ {width, height} 

As a result, the segmentation data can be subdivided into 32 subsets in terms of gender, finger, 

and the dimension, such as M_R2_w, M_R2_h, etc. In each subset of the 32 subsets, the 

statistical analysis was carried out. And the results, such as the number of data (i.e., the sample 

size), the median, the mean, the standard error (SE) of the sample mean, and the 95% confidence 

interval (CI) of the sample mean, are provided. The unit of the sizes in the segmentation data was 

in pixel, as requested, which is more accurate than other units. However, the results in terms of 

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the unit millimeter, which were converted from the results using the unit of pixel, are also 

provided. The statistical analysis regarding the age divisions is not included this time. 

The results of the statistical analysis are listed from Table 1 to Table 4. It is shown in these four 

tables that the median and the mean are quite close in each subset. This indicates that the 

distribution in each subset is quite symmetric. Therefore, the standard errors and the 95% 

confidence intervals of the sample mean instead of median were computed. The standard error 

for female is generally greater than the one for male. This is because the sample size for female 

is smaller than the sample size for male in the segmentation data. In addition, the size of the 

middle finger should be larger than the sizes of the index finger, the ring finger, and the little 

finger, respectively. However, this does not hold good for the subsets of male and heights (See 

Table 2 and Table 4). This is probably due to the segmentation issue. Nonetheless, while 

designing a simulated finger to be a target, the information for the widths is more important than 

the information for the heights. 

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Fingers Number Median Mean SE 95% CI 

M_R2_w 25913 296 294.82 0.18 (294.47, 295.16) 

M_R3_w 25913 304 303.32 0.18 (302.96, 303.68) 

M_R4_w 25913 296 294.24 0.17 (293.90, 294.57) 

M_R5_w 25913 272 271.30 0.19 (270.93, 271.68) 

M_L7_w 24809 288 290.50 0.18 (290.15, 290.85) 

M_L8_w 24809 304 300.23 0.18 (299.87, 300.59) 

M_L9_w 24809 288 288.14 0.18 (287.80, 288.49) 

M_L10_w 24809 268 266.52 0.19 (266.14, 266.90) 

F_R2_w 13341 272 270.24 0.24 (269.77, 270.71) 

F_R3_w 13341 274 275.08 0.25 (274.59, 275.58) 

F_R4_w 13341 270 268.39 0.23 (267.94, 268.84) 

F_R5_w 13341 240 242.38 0.25 (241.89, 242.88) 

F_L7_w 13434 262 263.31 0.23 (262.85, 263.76) 

F_L8_w 13434 270 267.91 0.25 (267.43, 268.39) 

F_L9_w 13434 257 258.73 0.23 (258.27, 259.18) 

F_L10_w 13434 232 232.32 0.25 (231.83, 232.81) 

Table 1 The statistical results for the widths in pixel of the 2nd, 3rd, 4th, and 5th finger of the right hand and the 

7th, 8th, 9th, and 10th finger of the left hand for both male and female, where the number stands for the sample 

size. 

Fingers Number Median Mean SE 95% CI 

M_R2_h 25913 472 470.29 0.27 (469.76, 470.82) 

M_R3_h 25913 480 478.22 0.32 (477.59, 478.85) 

M_R4_h 25913 486 484.37 0.31 (483.78, 484.97) 

M_R5_h 25913 424 420.05 0.30 (419.46, 420.63) 

M_L7_h 24809 464 467.15 0.27 (466.63, 467.68) 

M_L8_h 24809 480 476.07 0.34 (475.40, 476.74) 

M_L9_h 24809 488 487.26 0.30 (486.67, 487.85) 

M_L10_h 24809 416 413.33 0.33 (412.69, 413.97) 

F_R2_h 13341 432 428.76 0.37 (428.03, 429.49) 

F_R3_h 13341 440 440.30 0.42 (439.47, 441.12) 

F_R4_h 13341 434 435.88 0.42 (435.06, 436.69) 

F_R5_h 13341 376 375.41 0.39 (374.65, 376.18) 

F_L7_h 13434 426 424.58 0.36 (423.87, 425.29) 

F_L8_h 13434 438 438.44 0.41 (437.64, 439.25) 

F_L9_h 13434 432 434.20 0.39 (433.42, 434.97) 

F_L10_h 13434 374 372.65 0.40 (371.87, 373.43) 

Table 2 The statistical results for the heights in pixel of the 2nd, 3rd, 4th, and 5th finger of the right hand and 

the 7th, 8th, 9th, and 10th finger of the left hand for both male and female, where the number stands for the 

sample size. 

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Fingers Number Median Mean SE 95% CI 

M_R2_w 25913 15.04 14.98 0.0091 (14.96, 14.99) 

M_R3_w 25913 15.44 15.41 0.0091 (15.39, 15.43) 

M_R4_w 25913 15.04 14.95 0.0086 (14.93, 14.96) 

M_R5_w 25913 13.82 13.78 0.0097 (13.76, 13.80) 

M_L7_w 24809 14.63 14.76 0.0091 (14.74, 14.78) 

M_L8_w 24809 15.44 15.25 0.0091 (15.23, 15.27) 

M_L9_w 24809 14.63 14.64 0.0091 (14.62, 14.66) 

M_L10_w 24809 13.61 13.54 0.0097 (13.52, 13.56) 

F_R2_w 13341 13.82 13.73 0.0122 (13.70, 13.75) 

F_R3_w 13341 13.92 13.97 0.0127 (13.95, 14.00) 

F_R4_w 13341 13.72 13.63 0.0117 (13.61, 13.66) 

F_R5_w 13341 12.19 12.31 0.0127 (12.29, 12.34) 

F_L7_w 13434 13.31 13.38 0.0117 (13.35, 13.40) 

F_L8_w 13434 13.72 13.61 0.0127 (13.59, 13.63) 

F_L9_w 13434 13.06 13.14 0.0117 (13.12, 13.17) 

F_L10_w 13434 11.79 11.80 0.0127 (11.78, 11.83) 

Table 3 The statistical results for the widths in millimeter of the 2nd, 3rd, 4th, and 5th finger of the right hand 

and the 7th, 8th, 9th, and 10th finger of the left hand for both male and female, where the number stands for the 

sample size. 

Fingers Number Median Mean SE 95% CI 

M_R2_h 25913 23.98 23.89 0.0137 (23.86, 23.92) 

M_R3_h 25913 24.38 24.29 0.0163 (24.26, 24.33) 

M_R4_h 25913 24.69 24.61 0.0157 (24.58, 24.64) 

M_R5_h 25913 21.54 21.34 0.0152 (21.31, 21.37) 

M_L7_h 24809 23.57 23.73 0.0137 (23.70, 23.76) 

M_L8_h 24809 24.38 24.18 0.0173 (24.15, 24.22) 

M_L9_h 24809 24.79 24.75 0.0152 (24.72, 24.78) 

M_L10_h 24809 21.13 21.00 0.0168 (20.96, 21.03) 

F_R2_h 13341 21.95 21.78 0.0188 (21.74, 21.82) 

F_R3_h 13341 22.35 22.37 0.0213 (22.33, 22.41) 

F_R4_h 13341 22.05 22.14 0.0213 (22.10, 22.18) 

F_R5_h 13341 19.10 19.07 0.0198 (19.03, 19.11) 

F_L7_h 13434 21.64 21.57 0.0183 (21.53, 21.60) 

F_L8_h 13434 22.25 22.27 0.0208 (22.23, 22.31) 

F_L9_h 13434 21.95 22.06 0.0198 (22.02, 22.10) 

F_L10_h 13434 19.00 18.93 0.0203 (18.89, 18.97) 

Table 4 The statistical results for the heights in millimeter of the 2nd, 3rd, 4th, and 5th finger of the right hand 

and the 7th, 8th, 9th, and 10th finger of the left hand for both male and female, where the number stands for the 

sample size. 

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