Systems and methods are provided for determining a velocity or an inflation rate of a droplet in a microfluidic channel. The droplet is exposed to two or more temporally separated flashes of light, each flash including light of one wavelength band, and imaged using a detector configured to distinguish light in the wavelength bands. Two or more images of the droplet are acquired, each corresponding to one of the flashes, and all within a single video frame or photographic exposure. The images can be processed separately and the position or size of the droplet in each image is calculated. A velocity or inflation rate is then determined by dividing the change in position or size by the amount of time allowed to pass between the flashes.