Abstract: A method for analysing microscopic images of a blood smear allowing to determine the number of thrombocytes in a tested sample. The present disclosure uses an algorithm which allows for differentiating between platelets from other blood cells (including erythrocytes), and then counts the quantity of thrombocytes (number/?l) and determines their size (?m). The method includes providing a grayscale microscopic image of platelets, segmenting and analysing the image, wherein the step of segmentation and analysis of the image comprises analysing light regions of the image and analysing dark regions of the image, including detecting distinctive regions in the image using a maximally stable external regions algorithm; calculating for each light and dark region identified its convex hull and filtering the results obtained by shape; removing nesting regions; identifying aggregates; classifying cells into platelets and other blood constituents; and determining the number of platelets and masks thereof.