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Optical microscopy is an important technique in petrological and biological. However, because of the limited
focus depth of a traditional optical microscope, 3D objects can't be observed with all its information in one
scene. The commonly used method to solve this problem is to use a digital microscope to collect a sequence
of multi-focus images with a constant change of the focal length and then get the final sharp image by fusing
the images. Wavelet pyramid algorithm is one of the commonly used fusion algorithms and has a good
performance. In this paper, a novel 3D reconstruction algorithm is presented based on the wavelet pyramid
image fusion algorithm. First, a sequence of multi-focus images is collected with a digital microscope and
then the images are fused with the wavelet pyramid fusion algorithm. After that, the deviation between the
fused image and each of the original multi-focus images are calculated pixel by pixel. For convenience, the
absolute value of the deviation is calculated. The smaller the deviation, the closer the corresponding pixel to
the focal plane and vice versa. Thus a 3D deviation matrix is obtained. For each pixel position (x, y), the z
index of the smallest deviation value in the third direction of the deviation matrix is considered the pixel's
height index. A complete height index map is obtained by selecting the indices of these smallest deviation
values. In order to eliminate the noise effect, a median filter is applied to the height index map. The height
index map times the height factor (the unit step length along the optical axis when collecting the multi-focus
images) is the object's actual height map. Finally, the surface of the 3D object is reconstructed with the
object's height map. In order to test the reconstruction algorithm, a dedicated high resolution Complementary
Metal Oxide Semiconductor (CMOS) digital microscope is designed and fabricated to collect the multi-focus
images. Experimental results show that the proposed algorithm produces a nice looking surface of a 3D
object.
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