Fig. 1. Extension targets with different extension degrees. (a) Triangular; (b) heart; (c) five-point star; (d) smiling face; (e) tree; (f) fire balloon; (g) four-wing aircraft; (h) six-wing aircraft

Fig. 2. Six-wing aircraft with different θ. (a) θ=0; (b) θ=0.1; (c) θ=0.3; (d) θ=0.5

Fig. 3. Influence of partial missing of sub-aperture image on cross-correlation algorithm. (a) Extended target; (b) test-subimage;

Fig. 4. SURF feature matching preprocessing of partial missing sub-aperture images. (a) Extended target; (b) test-subimage;

Fig. 5. Optical path diagram of experiment

Fig. 6. Three sets of input aberrations to be measured. (a)‒(c) Generated three different sets of aberrations to be measured;

Fig. 7. Slope extraction error of objects with different extension degrees

Fig. 8. Slope extraction process based on SURF feature matching preprocessing

Fig. 9. Slope extraction error of extended objects when degree of missing is different. (a) Five point star; (b) four-wing aircraft ; (c) six-wing aircraft

Fig. 10. Effects of system resolution and SNR on slope extraction errors of SURF feature matching preprocessing. (a) Resolution is 48 pixel×48 pixel; (b) resolution is 32 pixel×32 pixel; (c) SNR is 20 dB; (d) SNR is 10 dB

Fig. 11. Schematic diagram of correlated Hartman sub-apertures. (a) Schematic of image partially missing; (b) ideal imaging target

Fig. 12. Extended object wave-front restoration results based on SURF feature matching preprocessing. (a1)(b1)(c1) When θ=0.4, wavefront recovery coefficient based on original cross-correlation of corresponding wavefront to be measured; (a2)(b2)(c2) when θ=0.4, cross-correlated wavefront recovery coefficient of corresponding wavefront to be measured based on SURF feature extraction; (a3)(b3)(c3) when θ=0.6, wavefront recovery coefficient based on original cross-correlation of corresponding wavefront to be measured is obtained; (a4)(b4)(c4) when θ=0.6, cross-correlated wavefront recovery coefficient of corresponding wavefront to be measured based on SURF feature extraction