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?
I think I might have been approaching this the wrong way. Rather than looking for a "zero point" on a filter, I think I should focus on applying the filter only when the user applies it, and trying to find a good starting point that is close to how the image looks without the filter for the initial value on the slider.