cocoa touch - Realtime access to iPhone's camera images -

i'm trying read (average) rgb-value of center pixel(s) of iphone camera. should happen in realtime. therefore open uiimagepickercontroller, use timer take picture every x seconds. processing picture made in separate thread such not block app while computing rgb-value. tried several ways access rgb/pixel values of taken image, have problem slow , cause camera view lag. tried following:

- (uicolor *)getaveragecolorofimage:(uiimage*)image { int pixelcount = kdetectorsize * kdetectorsize; cgcolorspaceref colorspace = cgcolorspacecreatedevicergb();  nsuinteger bytesperpixel = 4; nsuinteger bytesperrow = bytesperpixel * kdetectorsize; nsuinteger bitspercomponent = 8; unsigned char *rawdata = malloc(pixelcount * bytesperpixel); cgcontextref context = cgbitmapcontextcreate(rawdata, kdetectorsize, kdetectorsize, bitspercomponent, bytesperrow, colorspace, kcgimagealphapremultipliedlast | kcgbitmapbyteorder32big); cgcolorspacerelease(colorspace); cgcontextsetinterpolationquality(context, kcginterpolationnone);  nslog(@"drawing image"); cgcontextdrawimage(context, cgrectmake(0, 0, kdetectorsize, kdetectorsize), [image cgimage]); nslog(@"image drawn");  cgcontextrelease(context);  // rawdata contains image data in rgba8888 pixel format. alpha values ignored int byteindex = 0; cgfloat red = 0.0; cgfloat green = 0.0; cgfloat blue = 0.0;  (int = 0 ; <  pixelcount; ++i) {     red   += rawdata[byteindex];     green += rawdata[byteindex + 1];     blue  += rawdata[byteindex + 2];     byteindex += bytesperpixel; }  free(rawdata);  return [uicolor colorwithred:red/pixelcount/255.0 green:green/pixelcount/255.0 blue:blue/pixelcount/255.0 alpha:1.0]; } 

kdetectorsize set 6 such processed image has size of 6x6 pixels. 1 of image-parameter has been cropped 6x6 pixels before. slow part cgcontextdrawimage takes 500-600ms on iphone 4. tried alternatives line:

uigraphicspushcontext(context);  [image drawatpoint:cgpointmake(0.0, 0.0)]; uigraphicspopcontext(); 

or

uigraphicspushcontext(context);  [image drawinrect:cgrectmake(0.0, 0.0, kdetectorsize, kdetectorsize)]; uigraphicspopcontext(); 

both approaches slow 1 above. image size not have significant influence (i'd has no influence). know faster way access rgb value?

it ok, too, if thread not cause camera view lag. call thread that:

- (void)imagepickercontroller:(uiimagepickercontroller *)picker didfinishpickingmediawithinfo:(nsdictionary *)info {     uiimage *image = [info objectforkey:uiimagepickercontrolleroriginalimage];     [nsthread detachnewthreadselector:@selector(pickcolorfromimage:) totarget:self withobject:image];  }  - (void)pickcolorfromimage:(uiimage *)image {     nsautoreleasepool *pool = [[nsautoreleasepool alloc] init];        [nsthread setthreadpriority:0.0];      [...cropping image...] uicolor *averagecolor = [self getaveragecolorofimage:croppedimage];      [self performselectoronmainthread:@selector(applypickedcolor:) withobject:averagecolor waituntildone:no];        [pool release]; } 

thanks help!

you're approaching in wrong way - apple offer class want without messing around timers , uiimagepickers. avcapturesession , related classes give realtime access raw pixel data camera(s).

for more information refer documentation:

http://developer.apple.com/library/ios/#documentation/avfoundation/reference/avcapturesession_class/reference/reference.html%23//apple_ref/doc/uid/tp40009521