The Stimulus variable choice is used to select the correlation function for segmentation. Selection of a ``Stimulus'' generates a graphical plot of the stimulus function currently in use (provided that an image calculator graph window to be available). The parameters period/2, offset, iphase and deadtime are used to control the caracteristic shape and timing of the time curve. SQR is a normalised square-wave with duration and initial phase set in the Stim Params dialog box. ROI allows the user to define a function from the image sequence. The user marks the region on the image visible on the Sequence Tool Tv, typically the first image in the sequence. Clicking on the ROI button causes the program to build the correlation function using the image data within this region. On each frame in the sequence the average of the grey-level data within the ROI is calculated and used as the function sample. Once complete the mean of the function is computed and then subtracted from each sample and finally the function is normalised such that its sums to 1.
period/2 specifies the half-wave length of the square wave function SQR. The offset variable specifies the range of the phase search to be performed during the correlation. A value of 0 specifies in-phase detection only, i.e. no phase search. A value of 1 indicates that shifts of -1, 0 or +1 are allowable and similarly for other values. The correlation function is always performed over the minimum amount of data. iphase specifies the initial phase of the square-wave either +ve or -ve. The actual value is not important as the square-wave function is both mean subtracted and normalized.