How much influence the init_image has on the diffusion process. Values close to 1 will yield images very similar to the init_image while values close to 0 will yield images wildly different than the init_image. The behavior of this is meant to mirror DreamStudio's "Image Strength" slider.
This parameter is just an alternate way to set step_schedule_start, which is done via the calculation 1 - image_strength. For example, passing in an Image Strength of 35% (0.35) would result in a step_schedule_start of 0.65.