Image Fitting - Doing the Fit

You are now ready to perform the fit. Press the button to get the fit under way. If things are not set up correctly and the Fitting tool cannot proceed, then a pop-up window will tell you about the problem.

After a few seconds, a window will pop-up to show progress through the fit. Depending on the size of the data set, the complexity of the fitting function, the quality of the initial guesses and the pixel exclusion threshold, fitting can take quite a long time. The iterative Levenburg-Marquardt procedure is used.

What Happens When Fitting Fails?

• The data are too noisy to perform a fit.
• The data are corrupted by artefacts.
• The fit function is a poor match to the data.
• Fitting the model results in some fitted parameters which outside the min/max range for the parameters.

Any pixel where fitting fails will have a value in all output images which is either zero, or NaN (not-a-number). Which of these two is written to the images is controlled by a setting in the user preferences.