text: #import "GPUImageFilter.h"
  
  @interface GPUImageSharpenFilter : GPUImageFilter
  {
      GLint sharpnessUniform;
      GLint imageWidthFactorUniform, imageHeightFactorUniform;
  }
  
  // Sharpness ranges from -4.0 to 4.0, with 0.0 as the normal level
  @property(readwrite, nonatomic) CGFloat sharpness; 
  
  @end
  