for obtaining hemoglobin count in the blood of a mammal using digital images of the conjunctiva of the eye of the mammal taken with a camera of a mobile device running the mobile app the mobile app carries out a method including obtaining a color image of the conjunctiva of the eye using the digital camera computing an r b ratio and a y i ratio of the color image normalizing the r b ratio and the y i ratio using color image normalization parameters obtained using a master camera so as to provide a r b true ratio and a y i true ratio and using the r b true ratio and the y i true ratio as inputs to respective look up tables created using the master camera so as to provide an accurate measure of blood hemoglobin count application_number US 201414503379 A description with reference to fig1 an apparatus for calibration of cameras including mobile phone cameras and other cameras calibration tool 10 is shown in fig1 manufactured by en 39 urga inc the led lamp 12 of the calibration tool 10 is a full spectrum lamp placed inside a reflector 14 with a light diffuser 16 e g fusion optix u2122 so as to provide a relatively uniform back ground the lamp 12 is energized by the power cord 13 the camera 18 is focused onto.