Greetings! I believe this has something to do with the internal tables that are used for radiance conversion both in ENVI and IDL so I am posting this question to both fora: I converted DN values of a Landsat 1 image (dated 1973-2-27) to radiance values. I used MSS_CALDOIT routine for this. I realized that, in converting the Band 4 DN values, IDL used 127 as QCALMAX rather than 63 as suggested by the EOSAT bulletin (August 1986). Is this an erroneous operation on the part of IDL (ENVI too?) or is there a justification for that? PS1: I carried out the same operation for a Landsat 2 image (dated 1977-3-5) as well. In this case, IDL uses 63 as QCALMAX as suggested by the 1986 EOS bulletin. PS2: I have IDL 6.3, ENVI 4.3.