The invention is a method for estimating the amount of analyte in a fluid sample, and in particular in a bodily fluid. The sample is mixed with a reagent able to form a color indicator in the presence of the analyte. The sample is then illuminated by a light beam produced by a light source; an image sensor forms an image of the beam transmitted by the sample, from which image a concentration of the analyte in the fluid is estimated. The method is intended to be implemented in compact analyzing systems. One targeted application is the determination of the glucose concentration in blood.