Estimating phase for phase-stepping algorithms

A method of determining at least one phase offset of a fringe pattern in a captured image, said method comprising the steps of:

• receiving a captured image of a phase modulated fringe pattern, the captured image being one of a set of images captured with varying introduced phase offset;
• forming an intermediate demodulation image from the captured image, said intermediate demodulation image defining amplitude and complex phase parameters of the phase modulated fringe pattern;
• measuring the distortion for a plurality of locations in the intermediate demodulation image;
• applying a phase mask to the captured image based on the measured distortion, said phase mask defining a windowed region in the captured image having a predetermined amount of distortion;
• and
• determining at least one phase offset of the fringe pattern in the windowed region of the captured image.

A method of determining at least one actual phase offset of a fringe pattern in a captured image, said method comprising:

• (a) receiving a captured image having a phase modulated fringe pattern, the captured image being one of a set of images captured with varying introduced phase offset;
• (b) calculating carrier frequencies of the fringe pattern;
• (c) calculating, using a Fourier transform of the captured image and a window function, phases of the captured image;
• (d) demodulating from the calculated phases an intermediate demodulation image from the captured image, said intermediate demodulation image defining amplitude and complex phase parameters of the phase modulated fringe pattern including at least a phase offset value;
• (e) transforming the intermediate modulation image by a mask to produce a processed captured image having reduced effects of phase distortion, said mask being estimated from a function of at least one of the amplitude and complex phase parameters defined by the intermediate demodulation image;
• (f) updating the window function according to the mask;
• and
• (g) repeating at least steps (c) and (d) at least once with the updated window function and the processed captured image to iterate a further intermediate demodulation image having an updated phase offset value, said updated phase offset value being the actual phase offset.

A computer readable storage medium having a program recorded thereon, the program being executable by a computer to determine at least one actual phase offset of a fringe pattern in a captured image by performing the steps of:

• receiving a captured image having a phase modulated fringe pattern, the captured image being one of a set of images captured with varying introduced phase offset;
• forming an intermediate demodulation image from the captured image, said intermediate demodulation image defining amplitude and complex phase parameters of the phase modulated fringe pattern;
• transforming the captured image by a mask to produce a processed captured image having reduced effects of phase distortion, said mask being estimated from a function of at least one of the amplitude and complex phase parameters defined by the intermediate demodulation image;
• determining a Fourier transform of the processed captured image;
• and
• determining at least one phase offset of the fringe pattern in the processed captured image using the mask to identify interaction of peaks in the Fourier transform.

A computer readable storage medium having a program recorded thereon, the program being executable by a computer to determine at least one actual phase offset of a fringe pattern in a captured image by performing the steps of:

• receiving a captured image of a phase modulated fringe pattern, the captured image being one of a set of images captured with varying introduced phase offset;
• forming an intermediate demodulation image from the captured image, said intermediate demodulation image defining amplitude and complex phase parameters of the phase modulated fringe pattern;
• measuring the distortion for a plurality of locations in the intermediate demodulation image;
• applying a phase mask to the captured image based on the measured distortion, said phase mask defining a windowed region in the captured image having a predetermined amount of distortion;
• and
• determining at least one phase offset of the fringe pattern in the windowed region of the captured image.

A computer readable storage medium having a program recorded thereon, the program being executable by a computer to determine at least one actual phase offset of a fringe pattern in a captured image by performing the steps of:

• (a) receiving a captured image having a phase modulated fringe pattern, the captured image being one of a set of images captured with varying introduced phase offset;
• (b) calculating carrier frequencies of the fringe pattern;
• (c) calculating, using a Fourier transform of the captured image and a window function, phases of the captured image;
• (d) demodulating from the calculated phases an intermediate demodulation image from the captured image, said intermediate demodulation image defining amplitude and complex phase parameters of the phase modulated fringe pattern including at least a phase offset value;
• (e) transforming the intermediate modulation image by a mask to produce a processed captured image having reduced effects of phase distortion, said mask being estimated from a function of at least one of the amplitude and complex phase parameters defined by the intermediate demodulation image;
• (f) updating the window function according to the mask;
• and
• (g) repeating at least steps (c) and (d) at least once with the updated window function and the processed captured image to iterate a further intermediate demodulation image having an updated phase offset value, said updated phase offset value being the actual phase offset.

Imaging apparatus configured to determine at least one actual phase offset of a fringe pattern in a captured image, the apparatus comprising:

• means for receiving a captured image having a phase modulated fringe pattern, the captured image being one of a set of images captured with varying introduced phase offset;
• means for forming an intermediate demodulation image from the captured image, said intermediate demodulation image defining amplitude and complex phase parameters of the phase modulated fringe pattern;
• means for transforming the captured image by a mask to produce a processed captured image having reduced effects of phase distortion, said mask being estimated from a function of at least one of the amplitude and complex phase parameters defined by the intermediate demodulation image;
• means for determining a Fourier transform of the processed captured image;
• and
• means determining at least one phase offset of the fringe pattern in the processed captured image using the mask to identify interaction of peaks in the Fourier transform.

Imaging apparatus configured to determine at least one actual phase offset of a fringe pattern in a captured image, the apparatus comprising:

• means for receiving a captured image of a phase modulated fringe pattern, the captured image being one of a set of images captured with varying introduced phase offset;
• means for forming an intermediate demodulation image from the captured image, said intermediate demodulation image defining amplitude and complex phase parameters of the phase modulated fringe pattern;
• means for measuring the distortion for a plurality of locations in the intermediate demodulation image;
• means for applying a phase mask to the captured image based on the measured distortion, said phase mask defining a windowed region in the captured image having a predetermined amount of distortion;
• and
• means for determining at least one phase offset of the fringe pattern in the windowed region of the captured image.

Imaging apparatus configured to determine at least one actual phase offset of a fringe pattern in a captured image, the apparatus comprising:

• (a) means for receiving a captured image having a phase modulated fringe pattern, the captured image being one of a set of images captured with varying introduced phase offset;
• (b) means calculating carrier frequencies of the fringe pattern;
• (c) means for calculating, using a Fourier transform of the captured image and a window function, phases of the captured image;
• (d) means for demodulating from the calculated phases an intermediate demodulation image from the captured image, said intermediate demodulation image defining amplitude and complex phase parameters of the phase modulated fringe pattern including at least a phase offset value;
• (e) means for transforming the intermediate modulation image by a mask to produce a processed captured image having reduced effects of phase distortion, said mask being estimated from a function of at least one of the amplitude and complex phase parameters defined by the intermediate demodulation image;
• and
• (f) means for updating the window function according to the mask, wherein the processed captured image and the updated window function are used by means (c) and (d) at least once to iterate a further intermediate demodulation image having an updated phase offset value, said updated phase offset value being the actual phase offset.