JND Difference Calculator giving NAN values

I have been trying to calculate JNDs from an ROI on two different Cone Catch Images (same animal at different time points to quantify color difference between the images). When I use the “M” command to measure values in each selection, I find that the results table lacks labels and then when I run the “Colour JND Difference Calculator” under the “Data Analysis” section, I get an error message. When I have the ROIs in both images and use the “R” command to measure values in both simultaneously, the results table has labels. In this case, however, when I run the “Colour JND Difference Calculator” for the two regions between the images, the Comparison Results window that comes up gives an “NaN” value under “JND_diff”. I can’t seem to figure out why this is happening though or to get the “Colour JND Difference Calculator” to work. Any insights?

Thanks!

Chris