When editing photos on the iPad, there is full image filters and point-by-point turning. Full image filters, like what is used by most social sites, alter the image as a whole. Generally, there will be about a dozen filters, all or nothing. Snapseed is a solution that is popular as it allows for the tuning of how much of a filter is applied by sliding a finger across the screen. Which works great for those that have an idea of how tuning a filter will effect a photo.
The app, Gridditor, is for the rest of us. The Universal app (buy once and use on your iPad and iPhone) provides a grid view of how a image will look with a filter applied at a variety of percents. No guess work is involved. Choose a filter to use, then sweep through to pick the one that best matches the effect you were looking for. Gridditor works fast enough that it is possible to explore multiple filters and their impact at one time across a wide variety of strengths.