i need calculate standard deviation on image have inside uiimage object. know how access pixels of image, 1 @ time, somehow can it. i'm wondering if there somewhere in framework function perform in better , more efficient way... can't find maybe doensn't exist. know how this? bye
to further expand on comment above. using accelerate framework, depending on size of image. if image few hundred pixels few hundred. have ton of data process , accelerate along vdsp make of math lot faster since processes on gpu. little more, , possibly put code in few minutes.
update
i post code standard deviation in single dimension using vdsp, extended 2-d
float *imager = [0.1,0.2,0.3,0.4,...]; // vector of values int numvalues = 100; // number of values in imager float mean = 0; // place holder mean vdsp_meanv(imager,1,&mean,numvalues); // find mean of vector mean = -1*mean // invert mean when add subtraction float *submeanvec = (float*)calloc(numvalues,sizeof(float)); // placeholder vector vdsp_vsadd(imager,1,&mean,submeanvec,1,numvalues) // subtract mean vector free(imager); // free memory float *squared = (float*)calloc(numvalues,sizeof(float)); // placeholder squared vector vdsp_vsq(submeanvec,1,squared,1,numvalues); // square vector element element free(submeanvec); // free memory float sum = 0; // place holder sum vdsp_sve(squared,1,&sum,numvalues); sum entire vector free(squared); // free squared vector float stddev = sqrt(sum/numvalues); // calculated std deviation 
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