How to install
This version is compiled for windows and is compatible with Gimp 2.4

To install  just extract "unsharp2-0.1.12exe" and move it in your user plugin folder (usually in C:/document and setting/your name/gimp/plugin)

Then you will find it in the Filter menu, in Filters/Enhance/Unsharp mask2

TIPS

=== HOW  TO USE + EXTRA TIPS   ========================================================
 *
 * Radius is the radius as known from standard USM
 * Because here a fast infinite impulse response-filter is used, very high radius is possible without slowdown.
 * This comes in handy, when USM is used to enhance local contrast.
 * I do this often, and this was very very slow with gimp's original USM.
 *
 * I use a sony dsc f717 that is known for "flat" images (low contrast) and also for high dynamic
 * range. Using USM, rather than curves, I can enhance contrast without loosing shadows or highlights,
 * its just contrary: shadows and highlights get more (local) contrast, and no detail is lost.
 * (For real strong fill-flash effect a contrast mask must be used in gimp and afterwards local contrast
 * can be enhanced using USM)
 * ....................................................................................................
 *
 * Amount+ and Amount- are the amount factors, as known from USM, however, "+" means amount of
 * brightening and "-" means amount of darkening 
 * Threshold is the treshold as known from gimps USM
 * ....................................................................................................
 *
 * Gamma changes the gamma factor for internal processing. High gamma values can reduce sharpening halos.
 * The gamma of the resulting image is not changed.
 * (Try gamma of 5.0 and +/- amount upto 5.0. This sounds unreasonable, but it works very good )
 *
 * Why?
 *
 * Most digital cameras have a gamma value from 1.5 to 2.0.
 * When the image is in computer memory then the function between intensity i in nature and intensity 
 * value m in computer memory is : m = pow(i,1/g). (Where g ranges from 1.5 to 2.0)
 * Thats similar to a squareroot-curve.
 * When we apply USM to this unmodified image, then we get more bright halo than dark halo.
 * This looks very un-natural.
 * When we linearize data before doing USM, then we get equal amounts for dark and bright halos.
 * When we overcompensate g then we get dark halos, and in most cases these are unvisible or
 * look natural.
 *
 * ....................................................................................................
 *
 * Highlight-,Light-,Midtone-,Shadow Amount 
 * 
 * This can be used, to constrain the filter amount to darker or lighter areas of the image. 
 * Especially when USM is used to enhance local contrast it is useful.
 * For normal sharpening these sliders can be left at 1.0
 *
 * Preserve currently does nothing in sharpening mode.
 * In a later version this will protect color, that means it will prevent color artifacts 
 *
 * .......... Special feature, Blur and denoise ......................................................
 *
 * When both, Amout+ and Amount- are set to zero, then USM2 goes into blur mode.
 * The image is blurred with given radius.
 * The blurred image is copied into the Output image, where the given Threshold is used as
 * criteria. As long Threshold is 0.0 no blur happens. When Threshold is larger, then we get an effect
 * similar to selective gaussian blur. When Threshold is 1.0, then we get pure gaussian blur.
 * Gamma value can improve denoising results, it works with best selectivity at gamma values <= 0.5
 * Highlight Amount .... Shadow Amount can be used to constrain the filtereffect to brightness ranges.
 *
 * Because the same treshold can be used for sharpening and for denoising, this comes in handy when
 * USM has amplified some noise in sharpening mode, or when denoised pictures should be sharpened.
 *
 * Preserve protects original luminace while denoising/ blurring.
 * This comes in handy when we want to remove color noise in shadows before or after sharpening.
 *
 * I have also written  another denoising tool (dcamnoise). However, sometimes, when I see the results
 * which I get with this modified USM version here, then I am astonished what it can do, when the parameters are
 * carefully adjusted. Especially with low frequency noise (that is already filtered by camera firmware) it
 * is often better.
 *

Credit
this plugin was created by Peter Heckert , the windows bynary by courtesy of Michael Schumacher.
Source Code is included 
