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Artifacts Due to Pixel Correlation

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Authors:

(1) Hyosun park, Department of Astronomy, Yonsei University, Seoul, Republic of Korea;

(2) Yongsik Jo, Artificial Intelligence Graduate School, UNIST, Ulsan, Republic of Korea;

(3) Seokun Kang, Artificial Intelligence Graduate School, UNIST, Ulsan, Republic of Korea;

(4) Taehwan Kim, Artificial Intelligence Graduate School, UNIST, Ulsan, Republic of Korea;

(5) M. James Jee, Department of Astronomy, Yonsei University, Seoul, Republic of Korea and Department of Physics and Astronomy, University of California, Davis, CA, USA.

Table of Links

Abstract and 1 Introduction

2 Method

2.1. Overview and 2.2. Encoder-Decoder Architecture

2.3. Transformers for Image Restoration

2.4. Implementation Details

3 Data and 3.1. HST Dataset

3.2. GalSim Dataset

3.3. JWST Dataset

4 JWST Test Dataset Results and 4.1. PSNR and SSIM

4.2. Visual Inspection

4.3. Restoration of Morphological Parameters

4.4. Restoration of Photometric Parameters

5 Application to real HST Images and 5.1. Restoration of Single-epoch Images and Comparison with Multi-epoch Images

5.2. Restoration of Multi-epoch HST Images and Comparison with Multi-epoch JWST Images

6 Limitations

6.1. Degradation in Restoration Quality Due to High Noise Level

6.2. Point Source Recovery Test

6.3. Artifacts Due to Pixel Correlation

7 Conclusions and Acknowledgements

Appendix: A. Image restoration test with Blank Noise-Only Images

References

6.3. Artifacts Due to Pixel Correlation

In our generation of LQ images, we assume that the noise is Gaussian. However, in real astronomical images, especially when we create deep images by stacking many dithered exposures, there exist significant interpixel noise correlations. We find that these inter-pixel noise correlations create non-negligible artifacts.


Figure 13 display some examples of these artifacts. The LQ images here are sampled from multi-epoch drizzled images. The presence of correlated noise is apparent


Figure 9. Comparison of morphological parameters between MT-HQ and SG-LQ images (blue) and between MT-HQ and RS images (red). We follow the same format as in Figure 6. Note that the MT-HQ images have higher noise than the GT images created from the JWST images. Also, the SG-LQ images are noisier than the LQ images in the JWST dataset. Since SG images are in the geometrically distorted CCD coordinate, we applied the due transformation to the MT-HQ images in the rectified coordinate to align them with the SG images in the CCD coordinate. The properties measured in RS images are more closely correlated with those in MT-HQ images than those in the SG-LQ images.


Figure 10. Comparison of photometric information between MT-HQ and SG-LQ images (blue) and between MT-HQ and RS images (red). Significant improvements over the SG-LQ images are clear. In particular, the pixel-to-pixel comparison shows remarkable enhancement in both correlation strength and scatter reduction.


even from visual inspection. The RS images show that the correlated noise creates some low-surface brightness artifacts in the galaxy outskirts, which however are absent in the JWST images. Addressing this issue could involve strategies such as employing a different drizzling kernel for image stacking or leveraging more advanced deep learning algorithms. Exploring these solutions will be a key focus of our future work.


This paper is available on arxiv under CC BY 4.0 Deed license.


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