Gabriel Sechan wrote: >> From: [EMAIL PROTECTED] >>.. >>> From: [EMAIL PROTECTED] >>.. > My appologies- right concept, wrong terminology. This is a low-pass filter. > Its late, sorry. It passes through all values with an m close to 0, and > dumps those beyond a certain m. As such, it should be a gradual decrease > from (0,c) where c is the cutoff value, and a rapid decrease from (c,1). > Cutoff value is somewhere not long after .5. A m of .7 makes f=sqrt(p), > which if I remember is generally where you consider the cutoff, although it's > been a while since I've done filters. >
another characterization of m is that m is the value of p for which f=.5, or in one sense, m is the middle of the blend. > > This makes sense as a blend function. Imagine m is the distance between 2 > pixels. As m gets larger, the amount that second point counts into the blend > gets smaller and smaller, because log(.5)/log(m) becomes a higher positive > number (leading to a smaller result since p is less than 0). P is just the > pixel value of the second point. My guess is it runs this on a large number > of pixels and sums them to get the new value of the pixel its blending. Most > likely it takes the rgb (or cmy or whatever else it uses) and converts each > component to a value [0,1] and rune this equation on it. The only question > is how it gets m. m is a specified design parameter for [one segment] the gradient. Gradients can be user-created and edited. A simple gradient has one segment. The blend function used for each segment may be linear or one of 4 others, including this one called "curved" <heh>. This particular blend function does not seem much used in the collection of built-in gradients, and I was/am merely trying to satisfy my curiosity about it. > > If you want to play with it, you can adjust how much further away pixels are > taken into account by changing the .5 (raising it to make it use them more, > lowering it for less). If you reverse the division, you get a highpass > filter- it accepts the pixels further away more and the ones closer to it > less. Expect wacky results if you use that, since the least relevant data > will count for the most in your blend. I wouldn't seriously use any hand > rolled filter though- it takes deep black magic to create a good one, you > have to really know what you're doing. Its a lot of tradeoffs between cutoff > point, how well the cutoff point works (how quickly it goes down after it), > and how evenly the values in the filter are counted. OK, thanks. I will look at some plots and try to digest your descriptions. Regards, ..jim -- [email protected] http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-list
