## 5 Conclusions  
In conclusion, we have experimentally demonstrated the influence of the pixel intensity distribution of the speckle fields from the nonuniform pseudothermal light source on the measured CNR in microscale ghost imaging. The CNR of a ghost image is related to the speckles' pixel intensity distribution, which plays an important role in the CNR enhancement of ghost imaging. Thus, our experiments suggest that the CNR depends on the FWHM and the center position of the speckles' pixel intensity distribution.  
Our simulation analysis unambiguously identifies the speckles' pixel intensity distribution as one of the major limiting factors in the growth of the CNR. Furthermore, it offers  
Figure 4: Results of the pixel intensity distribution dependent simulation. The CNR rises nearly continuously with the width of the pixel intensity distribution, whereas the CNR decreases with the increasing peak position of maximum (**a**,**d**). Parameters matching the experimental data are highlighted with black lines. The corresponding objects (**b**) and pixel intensity distributions (**c**) are plotted and connected with dashed lines. Exemplary speckle patterns for selected parameters (**e**) visualize saturation effects, which lead to information losses at an increasing position of maximum. On the other hand, a broader pixel intensity distribution provides more information for the algorithm to work with.  
a general approach applicable to all fields of imaging where a higher CNR is needed and can be applied.  
Although we have not yet demonstrated the ghost imaging experiment in a relatively high CNR case with nanoscale resolution, it would be feasible by manipulating the speckle pattern and speckle size and optimizing the algorithm. Our study of the optimum speckle distribution in a wide range of parameters will be very important if ghost imaging will be implemented in wavelength regimes, e.g., in the extreme ultraviolet range (XUV), where the strong absorption of all materials reduces the possibility of manipulating light fields. Based on these findings it will be possible to develop an optimized light source that can pave the way for ghost imaging in the XUV. Ghost imaging in the XUV is very interesting because it will allow the taking of microscopic images with very high resolution whilst minimizing radiation damage.  
Data curation and writing--original draft preparation, Z.S.; methodology and formal analysis, F.T.; writing--review and editing, Z.S., F.T. and C.S.; supervision and funding acquisition, C.S.; All authors have read and agreed to the published version of the manuscript.  
This research was funded by Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy--EXC 2051 (Project-ID 390713860), \"Balance of the Microverse\"; GSI Helmholtzzentrum fur Schwerionenforschung GmbH & Postdoctoral Research Foundation of China, grant number GSI05 HGF-GSI-OCTC-2017; and Federal State of Thuringia and the European Social Fund (ESF) Project, grant number 2018 FGR 0080.  
Data Availability StatementData available on request due to restriction of privacy. The data presented in this study are available on request from the corresponding author. The data are not publicly available due to related experiments are still in progress and involve unpublished papers.  
We thank [PERSON] and [PERSON] for their help with preliminary experiments and [PERSON] for processing the samples.  
The authors declare no conflict of interest.