Photon Factory Activity Report 2016 #34 (2017)

BL-11A/2016G098

NOISE LIMITS CONDITION FOR IMAGE CORRECTION
IN SOFT X-RAY PROJECTION MICROSCOPY
Tatsuo SHIINA1*, Jamsranjav ERDENETOGTOKH1, Yasuhito KINJO2, Atsushi ITO3
1

Graduate School of Advanced Integration Science, Chiba Univ., Chiba-shi, Chiba, 263-8522, Japan
2
Tokyo Metropolitan Industrial Technol. Res. Inst., Koto-ku, Tokyo 135-0064, Japan3
School of Engineering, Tokai Univ., Hiratsuka-shi, Kanagawa, 259-1292, Japan

1 Introduction
In our study of soft X-ray projection microscope, toimprove the effectiveness of image correction, weevaluated the influence of background noise in the iteration
procedure through simulation study. In the simulation
study, images of a model specimen with known
morphology were used as a substitute for the chromosome
images taken at BL-11A beamline. Under the condition
that artificial noise was distributed on the images randomly,
we introduced two different parameters to evaluate noise
effects according to each situation where the iteration
procedure was not successful, and proposed an upper limitof the noise within which the effective iteration procedure
for the chromosome images was possible.
2 Experiment
Relationship between contrast of target in the corrected
image and noise MSE (Mean Square Error) on thesimulated projection image was examined for model
specimens with small (0.7 µm) and large (1.4 µm) squaresizes. The result is shown in Fig. 1. The horizontal axis is
noise MSE on the simulated projection image and thevertical axis is the contrast of the target on the corrected
image which was evaluated by the equation (1).
Contrast of target = 𝐺# − 𝐺% /𝐺'()

Fig. 1: Relationship between noise MSE of projection image
and contrast of target in corrected image.

(1)

where, G1 is an average value of the grayscale distribution
around the target in an area between the large square andthe small square. G2 is an average value of the grayscale
distributions on the target in the small square. Gmax (=216),
16 bit depth, is maximum value of the grayscale. “O” and“X” characters show correctable and uncorrectable regionof noise MSE, respectively. “A” indicates the contrast andnoise MSE of the current experimental image. Noise MSEof >105 decreases the contrast of target steeply, and it
should not exceed 105.
Some representative images with high and low noise
MSE are shown in Fig. 2 for the large specimens. In thefigures, the simulated projection images and theircorrected images are shown in the left and the right sides,respectively. Both images are shown for varying noise
MSE ranging from 4*105 to 4*106. The background noiseon the simulated projection images was prominent orinconspicuous for the images with high (106 and 4*106) or
low noise MSE (4*104 and 105), respectively. For thecorrected image with high noise MSE, the contrast of thespecimen image was lost by iteration procedure, resulting
in inability to identify its morphology.

Fig. 2:Iteration effects on the projection images with very low
contrast (large 1.4 µm square size).

References[1] T. Shiina et al., PF Activity Report 2015 #33 B (2016).
http://pfwww.kek.jp/acr/2015pdf/part_b/pf15b0363.pdf* shiina@faculty.chiba-u.jp