# Improvements of Computational Ghost Imaging by Using Sequenced Speckle
## 3 Experiments and Simulation Results
Lastly, for groups 1 to 4, with the same speckle size steps of 13.24 \(\upmu\)m within the speckle size range from 16.5 \(\upmu\)m to 496 \(\upmu\)m, the best CNR close to the TGI resolution can be found only in the group DG-1-5, -6 and DG-2-2, -3 for the DG-1 and DG-2 groups, respectively. For the DG-3 and DG-4 groups, the best CNR close to the TGI resolution can  
Figure 3:1 Evolution of the retrieved CNR and resolution of the SGI with different speckle composition groups (DG). (**a**) Experimental Results: the figure shows the evolution of the retrieved CNR and resolution for the SGI using different speckle composition groups (DG). For DG-1 and DG-2 groups, the best CNR values close to the TGI resolution are observed in DG-1-4, -5, -6, -7 and DG-2-3, -4, -5. In DG-3 and DG-4 groups, the group DG-3-2, -3 exhibits high-quality retrieved images. Similarly, for DG-5 and DG-6 groups, DG-5-3, -4 and DG-6-2, -3 demonstrate higher CNR values and improved resolution. In DG-7 and DG-8 groups, the high-quality reconstructed images can be found in DG-7-2, -3 and DG-8-2. (**b**) Simulation Results: the simulation results show a similar trend in the correlation between image quality and speckle size as observed in the experimental results. be found only in the group DG-3-2. Although these groups have similar resolutions, DG-1-6 and DG-2-2 demonstrate better performance in terms of ghost image quality. Moreover, when arranging the results by multiplying the values of CNR and resolution in ascending order, DG-2-5 exhibits the highest value of 2.45. Our numerical simulations also indicate that these sequenced speckle pattern groups yield a better CNR with competitive resolution compared to the TGI. In summary, we observe that better image quality can be achieved using the speckle patterns from the groups DG-1-6, DG-2-3, DG-2-5, DG-3-2, DG-6-2, and DG-6-3 in the SGI. Additionally, when arranging the results by multiplying the values of CNR and resolution in ascending order, DG-2-5 exhibits the highest value of 2.45. This can be calculated using CNR and resolution and verified visually. The best-performing groups can be easily identified from the summary provided in Figure 3:2 By carefully selecting the speckle sequence, significantly improved imaging quality compared to the TGI can be achieved. To further analyze the SGI groups, we summarize the speckle distribution of the typical groups with resolutions close to the TGI, considering a speckle size of 164.5 \(\upmu\)m. Since the four small windows of the window-shaped object can be treated as independent small objects, we use the smallest window as a reference. Given the uniform distribution of speckle patterns that can completely cover the object in the experiment, the imaging quality of each small window is very similar. Hence, we consider the smallest window as the reference object. By considering CNR and resolution comprehensively, we find that the speckle distribution of the majority of groups is within the range of 164.5 \(\upmu\)m to 303 \(\upmu\)m (Figure 10). It appears that the best image quality in the SGI is achieved when the speckle area covers approximately 0.3 to 1 times the reference object area. This provides a reference for further optimizing the imaging quality of the SGI. To verify the advantages of the SGI in reducing the number of necessary iterations, we plot the CNR curves for different iterations for the best groups in the SGI. Typically, a better image quality can be obtained from the object with more iterations, but at the expense of longer imaging time. In order to compare the CNR of the retrieved ghost images more intuitively, we select 11 groups from the SGI with better CNR and resolutions between 1.0 and 1.1. As shown in Figure 10, the CNR significantly improves as the number of iterations increases. For the TGI, after 9000 iterations, the CNR at the speckle size of 164.5 \(\upmu\)m is considered as the standard with a value of 1.8873.