It is hard to say from the photos but these areas might be roughstalk bluegrass, Poa trivialis.  There is some tall fescue in the corner of the photo.  Tall fescue has a much wider blade than traditional Kentucky bluegrass.  

Roughstalk bluegrass can form unsightly light-colored patches in lawns. Roughstalk bluegrass is a perennial grass that thrives in moist, shady, or over-watered areas. Patches enlarge in the soil by stolons, which are modified above-ground stems. These stolons are not well-rooted in the soil. Therefore, these patches can dry out during hot, dry summer months.  

Unfortunately, there are no selective herbicides for control of roughstalk bluegrass. Patches may be controlled with one or two applications of glyphosate (Roundup, others). Once these patches are removed you can reseed.  Many cultural practices can discourage the growth of roughstalk bluegrass, such as deep and infrequent watering, high mowing height, and good drainage to remove excess water.
For residential lawns, there are not a lot of options for removing weedy grasses from desired grasses.  In most cases killing off the grass or digging up the patches and then reseeding is the only option.