Statistics of local speckle contrast

Area of Science:

• Optics and Photonics
• Image Processing
• Biomedical Imaging

Background:

• Laser speckle contrast is typically assumed to be unity in first-order analysis.
• Localized spatial region calculations in processing schemes often yield contrast values deviating from unity.

Purpose of the Study:

• To characterize the distribution of local laser speckle contrast.
• To model the local contrast using a log-normal distribution.
• To establish relationships between model parameters and physical properties like speckle size.

Main Methods:

• Analysis of local contrast calculated over localized spatial regions.
• Modeling the local contrast distribution using a log-normal probability distribution function.
• Expressing model parameters in terms of minimum speckle size and local neighborhood extent.
• Validation using Optical Coherence Tomography (OCT) data.

Main Results:

• Local laser speckle contrast exhibits a distribution of values that can differ from unity.
• A log-normal distribution accurately characterizes the local contrast.
• The parameters of the log-normal model are dependent on the minimum speckle size and the size of the local neighborhood used for calculation.

Conclusions:

• The local contrast of laser speckle is not always unity and follows a predictable distribution.
• The log-normal model provides a robust framework for understanding local speckle contrast variations.
• This model offers insights into data acquisition parameters and their impact on speckle analysis, particularly in OCT.