ios - Using the C API for ImageMagick (on iPhone?) to convert to monochrome? -

i using code referenced in this post, switch imagemagick c-api based solution, want standardize on single image manipulation library, , need im other tasks.

i can find tons of examples of using convert command line tool, none on how monochrome conversion in code.

any sample code out there?

you can achieve monochrome conversion, described here, magickquantizeimage function. i'm not quite familiar dithering images, example may following.

#include <wand/magickwand.h>  int main(int argc, char **argv)  {   const size_t number_colors = 2;   const size_t treedepth     = 1;   magickwandgenesis();   magickwand *wand = null;   wand = newmagickwand();   magickreadimage(wand,"source.png");   magickquantizeimage(                      wand,            // magickwand                      number_colors,   // target number colors                      graycolorspace,  // colorspace                      treedepth,       // optimal depth                      magicktrue,      // dither                      magickfalse      // quantization error                  );   magickwriteimage(wand,"out.png");   if(wand)wand = destroymagickwand(wand);   magickwandterminus();   return 0; } 

this can give rather speckled image @ times.

adjusting depth, color-number, and/or disabling dithering may give results closer expect examples provided.

magickquantizeimage(                    wand,            // magickwand                    number_colors,   // target number colors                    graycolorspace,  // colorspace                    treedepth,       // optimal depth                    magickfalse,     // no-dither                    magickfalse      // quantization error                ); 

like such...

for ios

not effort needed port example code ios. nextstep/objective-c methods compatible magickwand library. following example uses temporary file store monochrome image, i'm sure there better way pass magick image-data directly uimage object.

// myviewcontroller.h #import <uikit/uikit.h> #import <wand/magickwand.h>  @interface myviewcontroller : uiviewcontroller  @property (retain, nonatomic) iboutlet uiimageview *imageview; @property (retain, nonatomic) magickwand *wand;  @end  // myviewcontroller.m #import "myviewcontroller.h"  @implementation myviewcontroller  - (void)viewdidload {     [super viewdidload];     magickwandgenesis();     self.wand = newmagickwand();     [self drawmonochromeimage:@"logo:"]; }  -(void)drawmonochromeimage:(nsstring *)filepath {     // create temporary file     nsstring *tempfilepath = [nstemporarydirectory()                                   stringbyappendingpathcomponent:@"logo.jpg"];      // read given image c-string     magickreadimage(self.wand,         [filepath cstringusingencoding:nsasciistringencoding]     );      // monochrome image     magickquantizeimage(self.wand,2,graycolorspace,1,magickfalse,magickfalse);      // write temporary file     magickwriteimage(self.wand,         [tempfilepath cstringusingencoding:nsasciistringencoding]     );      // load uiimage temporary file     uiimage *imgobj = [uiimage imagewithcontentsoffile:tempfilepath];      // display on device     [self.imageview setimage:imgobj];     [self.imageview setcontentmode:uiviewcontentmodescaleaspectfit]; } -(void)viewdidunload {     // clean-up     if (self.wand)         self.wand = destroymagickwand(self.wand);     magickwandterminus(); }  @end