Hello Dimitris,
I think I found how OPtris stores the temperature in second plane of tiff files. They are stored as RGB 3 band 8bit bit, the red band contains all 0 values, green all 247 or 248 value and blue band contains temp deg Celsius * 10...see attachement where I transform the 2nd plane image into a list of bytes that is like [0, 247, 190, 0, 247, 191,....] see attachment
PS. actually this is true for blue values less than 255 so it is more cpmplicates to extract temperature....