Fig. 1. Principle of symmetry of parallel-beam projection data. (a) Parallel-beam CT scanning; (b) projection sinogram

Fig. 2. Schematic diagram of COR calibration algorithm under displaced CT scanning. (a) Detector unit position; (b) symmetric transformation of projection data

Fig. 3. Projection images with noise from different views. (a) 0; (b) 90°; (c) 180°; (d) 270°

Fig. 4. COR calibration results with different displaced sizes

Fig. 5. Redundancy and weighting function of projection data under displaced scanning^[32]

Fig. 6. Reconstruction results of SCD algorithm and PDP algorithm. (a) Supplementary projection data; (b) reconstruction result of SCD algorithm; (c) projection weighted processing; (d) reconstruction result of PDP algorithm

Fig. 7. Error analysis of SCD reconstruction algorithm. (a) Supplementary projection data; (b) ideal result of ROI-1; (c) supplementary result of ROI-1; (d) ideal result of ROI-2; (e) supplementary result of ROI-2

Fig. 8. CT reconstruction results of SCD algorithm. (a) Result of SCD algorithm; (b) ROI results

Fig. 9. CT reconstruction results of PDP algorithm. (a) Projection processing; (b) result of PDP algorithm; (c) ROI reconstruction results

Fig. 10. Comparison of image quality reconstructed by different algorithms. (a) SSIM; (b) PSNR; (c) AG; (d) SF

Fig. 11. Comparison of image quality under different COR positions. (a) SSIM; (b) PSNR; (c) AG; (d) SF

Fig. 12. Displaced scanning projection data of the sample. (a) 0; (b) 90°; (c) 180°; (d) 270°; (e) projection sinogram; (f) D(s) curve

Fig. 13. Projection sinograms and reconstructed image of Mg-Al alloy sample under displaced scanning. (a) Projection sinogram; (b) sinogram after WANG weighted function preprocessing; (c) reconstructed image

Fig. 14. Reconstructed images and volume rendering results of Mg-Al alloy sample