After creating a mspec file my mean check of the grey standards in my photo do not always match the lrvs I have set for each of them. What are some potential reasons as to why this is happening and how concerned should I be (i.e. how “off” of the set lrv is too “off” for a set of measurements in the color channels?)? We would like to have absolute results to compare to future studies if possible, but will settle for relative results within this one experiment if necessary.

Potential ideas for the discrepancies:

  • grey standards are submerged in water and photographed in air
  • clear tape is used to keep the grey standards in place and prevents water from disintegrating them (standards created using paint swatches)
  • some way in which the program calculates the measurements and possible the number of standards (n = 5 – I know it’s not necessary to use that many, but we wanted to try a couple of exploratory analyses) I used to create the mspec file
    • Note: I did play around with setting different grey standards, different numbers of grey standards, and estimating the black point to see if the measurements for each standard were closer to their true lrvs, but didn’t have much luck. I’m going to play around with a couple of other iterations of test photos, but suspect the results will be no different.

Any and all suggestions will be greatly appreciated. Thanks!

mean of grey standard doesn’t match set lrv
jolyon Answered question February 21, 2020