eSRRF Estimating maximum frame number
This function allows you to estimate the maximum number of frames to use for eSRRF reconstruction before motion blur starts compromising the potential resolution achieved. This is done from a continuous time series dataset by computing the Structural Similarity (SSIM) on a frame by frame basis with increasing frame separation. As the number of frames separating 2 frames increases, the SSIM naturally decreases. This SSIM plot is calculated for all available range of length determined by block size, so block size should be set to a value that's a little bigger than what the user might expect to be the number of frames to use.
The smoothing factor allows the curves to smooth over time and the sigma value determines where the cut-off position sits. For instance, a value of 2 sigma for the cut-off means that the mean SSIM value needs to have dropped by at least twice the standard deviation of the SSIM value to be considered significantly different from the first frame, therefore indicating a significant change in the structural content of the image. The cut-off therefore represents the maximum number of frames to use for the eSRRF reconstruction.
The calculation of the SSIM requires the use of regularisation factors, which can either be selected from the total bit depth of the image (for instance 0-255 for 8-bit images) or from the dynamic range of the intensity values within the image.
If you expect the dynamics that you recorded to change over time, you can tick the Calculate cut-off over time, and it'll be estimated over time on top of the general cut-off estimation. This cut-off over time estimation is less accurate however.
We recommend to crop the data to a specific area of interest to improve accuracy and speed of the analysis.