# Resolution Enhancement of Spherical Wave-Based Holographic Stereogram with Large Depth Range +
###### Abstract  
The resolution-priority holographic stereogram uses spherical waves focusing on the central depth plane (CDF) to reconstruct 3D images. The image resolution near the CDP can be easily enhanced by modifying three parameters: the capturing depth, the pixel size of elemental image and the focal length of lens array. However, the depth range may decrease as a result. In this paper, the resolution characteristics were analyzed in a geometrical imaging model, and three corresponding methods were proposed: a numerical method was proposed to find the proper capturing depth; a partial aperture filtering technique was proposed after reducing pixel size; the moving array lenslet technique was introduced after increasing focal length and partial aperture filtering. Each method can enhance resolution within the total depth range. Simulation and optical experiments were performed to verify the proposed methods.  
olographic stereogram; spherical wave; depth range; resolution enhancement; aperture filtering +
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acquisition of depth information is not easy. The ray sampling (RS) plane method enhances the resolution by setting the RS plane near the object to sample high resolution projection image [21; 22]. The moving array lenslet technique (MALT) was used to enhance the sampling rate of HS without decreasing the angular resolution [23]. The compressive light field could be encoded into a hologram to relieve the spatio-angular resolution trade-off in conventional HS [24]. Recently, we have proposed a new concept of HS which is called the resolution priority HS (RPHS) [25]. The RPHS is obtained by adding a quadratic phase term on the conventional FFT of EIs. Different from conventional HS which uses multiple plane waves to reproduce light field, the RPHS uses spherical waves focusing on the central depth plane (CDP) to reconstruct 3D images. The spherical waves form smaller volume pixels (voxels), thus resulting in enhanced resolution.  
In this paper, the resolution of RPHS is analyzed in a geometrical imaging model. Three parameters, capturing depth, pixel size of EI and focal length of the lens array, mainly determine the resolution. It is found that simply modifying the three parameters may enhance the image resolution near the CDP, at a price of decreased depth range. To enhance resolution within the total depth range, three methods are proposed. Firstly, A numerical method is proposed to find the proper capturing depth. Secondly, after reducing pixel size of EI for the resolution enhancement near the CDP, a partial aperture filtering technique is proposed to limit the light ray width for resolution enhancement away from the CDP. Lastly, after increasing focal length of the lens array for the resolution enhancement near the CDP, partial aperture filtering is used to limit the light ray width, which results in dark gaps. The moving array lenslet technique is introduced to fill in the dark gaps.