Flash boiling sprays have demonstrated great potential in improving fuel atomization and evaporation even at very low injection pressure. In this study, fuel spray characteristics of three gasoline direct-injection injectors, namely, a one-hole injector, a six-hole injector, and a one-slot injector, were investigated via high-speed Schlieren technique. Experimental results reveal that different transformations of spray geometry were identified under various test conditions. Under flare flash boiling conditions, an expanded spray structure was observed of the one-hole injector, but collapse sprays were found of the six-hole injector and one-slot injector. The spray collapse led to longer spray penetration of the six-hole injector, but for the one-slot injector, the spray penetration decreased. To unveil this phenomenon, a two-dimensional transparent nozzle was designed to investigate the inner nozzle flow using high-speed microscopic backlit imaging technique. It showed that the vapor bubble was initiated inside the nozzle along the nozzle wall under transition and flare flash boiling conditions. Both vapor bubble size and volume fraction increased with increasing superheat degrees. Much bigger vapor bubbles and larger volume fraction were found under the flare flash boiling conditions. Both in-nozzle vapor bubbles and fuel boiling effect at the nozzle exit contributed to rapid fuel atomization and evaporation process. Contraction or expansion of the spray geometry was dependent on whether in-nozzle bubble or fuel boiling played the dominant role. In summary, more physical insights were revealed into the collapse phenomena and rapid atomization process of flash boiling sprays.