A calibration method for calibrating a camera for detecting an analyte in a sample is disclosed. A plurality of different color coordinate systems and a set of test samples are provided. The test samples are applied to test elements that have test fields for producing an optically detectable reaction. Images of the colored test fields are acquired using the camera and color coordinates for the images are generated. The color coordinates that are generated are transformed into a set of measured concentrations by using a set of coding functions. The set of measured concentrations is compared with the known concentrations of the test samples and a best match color coordinate system of the plurality of color coordinate systems is determined. A best match coding function of the plurality of coding functions is also determined.