Method for observing a sample, by calculation of a complex image

A method for observing a sample comprising:

• a) illuminating the sample using a light source, configured to emit a light wave that propagates towards the sample;
• b) acquiring, using an image sensor, an image of the sample, the image being formed in a detection plane, the sample being placed between the light source and the image sensor, the acquired image being representative of a light wave transmitted by the sample under the effect of the illumination, the acquired image comprising interference patterns formed by interference between the light wave emitted by the light source and a light wave diffracted by the sample;
• and
• c) calculating a complex image representative of the sample;
• wherein calculating the complex image representative of the sample comprises:
• i) defining an initial image of the sample in the detection plane, on the basis of the image acquired by the image sensor;
• ii) determining a complex image of the sample in a reconstruction plane by applying a propagation operator to an initial image of the sample, which is the image defined in i), or to the image of the sample, in the detection plane, resulting from the preceding iteration;
• iii) calculating a noise indicator on the basis of the complex image obtained in ii), the noise indicator depending on a reconstruction noise affecting the complex image, the noise indicator being representative of fluctuations appearing in the complex image;
• iv) updating the image of the sample in the detection plane by adjusting phase values of the pixels of the d image, the adjustment being carried out depending on a variation in the noise indicator calculated in iii) with respect to the phase values;
• v) reiterating ii) to iv) until a convergence criterion is reached, so as to obtain a complex image of the sample in the detection plane, or in the reconstruction plane.