**2.2.2 The block size**

In BMA, the size of a block is another important factor to influence the matching precision and the complexity. If the block is too small, the matching information is limited and it would influence the matching precision greatly. While if the block is too large, the deformation during movement cannot be omitted. Besides, the larger block can result in a large computational burden. Therefore, to research the relationship between the block size and the object function is meaningful.

A standard grid used as the target object is shown in Fig.2, the magnification of the microscope's objective lens is 60 , which means that the underlying image is very smooth. The black squares designate the "blocks". First, we tested the matching error of different object functions on different block sizes. The results are shown in Fig.3, where the vertical axis denotes the estimation errors, with unit of pixel; the horizontal axis denotes the block size, with unit of pixels.


Fig. 2. The standard grid micrograph

In BMA, the size of a block is another important factor to influence the matching precision and the complexity. If the block is too small, the matching information is limited and it would influence the matching precision greatly. While if the block is too large, the deformation during movement cannot be omitted. Besides, the larger block can result in a large computational burden. Therefore, to research the relationship between the block size

A standard grid used as the target object is shown in Fig.2, the magnification of the microscope's objective lens is 60 , which means that the underlying image is very smooth. The black squares designate the "blocks". First, we tested the matching error of different object functions on different block sizes. The results are shown in Fig.3, where the vertical axis denotes the estimation errors, with unit of pixel; the horizontal axis denotes the block

1. The estimation error of NCC is sensitive to the block size and has no obvious rule. Therefore if one wants to estimate the sub-pixel shift between two images by using

2. The estimation error of LSAD is sensitive to the block size too, the larger the block size is selected, the smaller the estimation errors. Thus, with respect to the LSAD sub-pixel

3. As far as other functions are concerned, including SSD and ZSAD, they have the similar estimation results which can achieve much smaller errors comparatively, and they are

4. As far as the standard grid block, the most appropriate size is 50 50 pixels, which includes an integral corner of a white grid and a little black background. It proves this kind of block both can express the internal difference of the block approximately and

NCC, the block size should not be the main regulating parameter.

estimation, it is often beneficial to increase the block size.

can eliminate the coupling between *x* and *y* direction.

not sensitive to block size as NCC and LSAD.

Fig. 2. The standard grid micrograph

**2.2.2 The block size** 

size, with unit of pixels.

and the object function is meaningful.

Fig. 3. Estimation errors with different block size
