Fourfold-N step phase-shifting images

This data is for Fourfold-N step phase shifting method. There are three types of images here and in each type : '1. bmp', '5. bmp', '9. bmp', and '13. bmp' are the first set of data, '2. bmp', '6. bmp', '10. bmp', and '14. bmp' are the second set of data, '3. bmp', '7. bmp', '11. bmp', and '15. bmp' are the third set of data, and '4. bmp', '8. bmp', '12. bmp', and '16. bmp' are the fourth set of data. And 'g1. bmp', 'g2. bmp', 'g3. bmp', and 'g4. bmp' are Gray code images with auxiliary phase unwrapping.