Slider settings for GPUImage

Slider settings for GPUImage

I'm making an app which allows the user to apply GPUImage filters to still
photos using a UISlider. I'd like for the slider to initially start at the
zero point for each filter (i.e. the value at which none of the filter has
been applied yet) and I'm wondering how this can be determined? I've used
some of the values that are listed in the GPUImage documentation and for
certain sliders they start at 0, but others it's hard to determine (and
for some, the min and max values are way off for me). The values for
something like GPUImagePosterizeFilter seem to be way off for me (set min
to 1, max to 128 and initial to 1). I've also checked some of the values
in the FilterShowcase test project which are different than the
documentation, but still don't always start at 0. Am I just completely
missing the point here? Or is there some setting I maybe have to turn on
to be in line with the slider values?