I have been reading about Speckle Contrast Imaging recently. Its quite an interesting topic given that it should be possible with relatively inexpensive equipment. The basic premise from what I gathered is as follows:
- A laser beam forms a "speckle" pattern when shined on a surface due to random interference
- Motion of the scattering species e.g. blood cells can cause these speckles to "blur"
- The blurring of these speckles can be used to highlight the motion of the scattering species
The contrast ratio $K = \frac {\sigma}{<I>}$ quantifies the blurring of the speckles. $\sigma$ is the standard deviation of an $N\times N$ cluster of pixels while $<I>$ is the mean intensity. Iterating over an entire image (e.g. $1024\times 1280$ pixels) would yield a value of $K$ for each pixel which can be used to "construct" a new image, highlighting the scattering species.
Now there is some terminology related to the topic which I'm not sure about. Many of the sources I have seen mention "Spatial Contrast" and "Temporal Contrast".
An example source: Laser speckle contrast imaging in biomedical optics
Could someone explain the differences between these and what they would mean from a practical point of view? Thanks!
Best Answer
Spatial would mean that we have one image, smooth areas are where there was motion and the image looked smooth/constant value .... rough spots are observed where motion is less, i.e the area shows lots of variation/contrast in intensity.
Temporial would require video or a changing of signal with time, like looking at a whole surface that started or stopped moving.
With a video you could do both spatial and temporal at the same time. Watching blood cells move under a smooth surface.