Joe Tschudi wrote: > Hello, > > I am getting weird results out of spec2cie when converting spectral data to > CIE data by > using a custom illuminant. First I tried spotread (spotread -v -s -c1 -a > CustomTest_spotread.sp) to get ambient emission curves to be saved as an .sp > file. I > also tried illumread (illumread -v -c1 CustomTest_illumread.sp) but the > results after > converting with spec2cie are even further off. I have spectral remission data > that I > measured using the same device (i1Pro 2) with chartread (chartread -v -c1 -p > -L -S > TEST) which I am trying to convert from spectral data to LAB using the custom > illuminant with spec2cie -v -n -i CustomTest_xxx.sp spectral.ti3 cie.ti3 Hi, CustomTest_illumread.sp seems a little strange. specplot shows a CT of 8098K, and an L*a*b* compared to D50 of 100.000000 -12.215330 -27.322065, which is quite blue. > Although the CCT of the emission curves shows me a value of around 5850K I am > getting > LAB results that are completely blueish and have nothing to do anymore with > the > original spectral color. To compare the results I am using Bruce Lindbloom's > Spectral > Calculator Spreadsheets (10nm) (http://www.brucelindbloom.com -> Calc -> > Spectral > Calculator Spreadsheets -> scroll down for 10nm Download) where it's possible > to fill > one custom spectral (remission) column and a custom (emission) illuminant and > the > results there are correct IMHO. > > Using regular spec2cie with -i D50 I get: 2° LAB 91.21 / 0.15 / 4.34 > > With the Spreadsheet I get: 2° CustomIlluminant_spotread: LAB 91.12 / -0.47 > / 4.49 2° > CustomIlluminant_illumread: LAB 91.04 / -1.12 / 4.50 > > With spec2cie I get: 2° CustomIlluminant_spotread: LAB 91.12 / -4.29 / -4.91 > 2° I'm not sure why you think that is in error. CustomIlluminant_spotread is bluer than D50 (L*a*b* of 100.000000 -4.141052 -10.421183), so there is no surprise that your samples illuminated by a bluer light has a bluer XYZ value. Beware of the difference between reflectance values and absolute XYZ values though. It's also not clear what the white reference is for the conversion to L*a*b* in Bruce Lindbloom's spreadsheet. If it uses the custom illuminant as the white reference rather than D50, then naturally you will get a more neutral set of numbers to the spec2cie result. Graeme Gill.