The temperature and velocity field variations of ventilation flow in the passenger compartment were measured simultaneously by using a digital image processing technique. A 1/10 scale vehicle was used for panel-vent mode heating. Micro-encapsulated TLC (Thermochromic Liquid Crystal) particles were used as a reliable tracer for temperature and velocity measurement. Particle color images captured with a 3 CCD (Charge Coupled Device) color video camera were used for calculating the velocity and temperature fields at the same time. To measure the temperature field variations, the HSI (Hue, Saturation, Intensity) true color image processing of TLC particles was applied to the TLC color images. A 2-frame particle tracking velocimetry using the concept of match probability between two consequent image frames was applied to the TLC particle displacements in order to measure the velocity field variations in the passenger compartment. The temperature and velocity fields measured simultaneously are well matched with each other and give reliable information on the ventilation flow.