This research is aimed to introduce and to compare 3 methods of reading out and analysing light blue radiochromic film (BLF) dosimeter and red radiation-sensitive poly-methylmethacrylate (PMMA). BLF and red radiation-sensitive PMMA act as a colour detector which its colour changes after being irradiated. These dosimeters are usually used in food irradiation for process control during irradiation process. We used camera-based measurement in a constraint condition, scanner-based measurement with our own software (Trichromatic Colour Analyser, TCA) and spectrophotometer for obtaining colorimetric data of both dosimeters which were non-irradiated and irradiated in 5 different doses: 5, 10, 15, 20 and 25 kGy, ranged for food application. There were strong linear relationships, for all 3 methods, between doses, given to BLF, and lightness (CIE L$^*$), chroma (CIE C$^*$) and yellowness-blueness (CIE b$^*$). For red radiation-sensitive PMMA, strong linear relationships were found between doses and redness-greenness (CIE a$^*$) as well as CIE C$^*$ in both TCA and spectrophotometer methods. The doses and CIE L$^*$ gave strong relationship only in the spectrophotometric method.