The present study aims to assess the deformability of Red Blood Cells (RBCs) under extensionally dominated microfluidic flows using an image based technique. For this purpose, a microchannel having a hyperbolic shaped-contraction was used and the images were captured by a standard high-speed microscopy system. The images acquired display RBCs with various light intensity levels and image analysis was used to quantify the Deformation Index (DI) of the RBCs considering these light intensity differences. Additionally, the velocities of different intensity-level RBCs flowing along the centerline of the channel were measured using particle tracking velocimetry. The preliminary results at two different flow rates reveal a highly deformable nature of RBCs when submitted to strong extensional flows. It was also observed that the low intensity cells exhibit a slightly higher velocity than intermediate intensity cells, which we attribute to the cells being located in different planes.