Effecient algorithms for image pixel manipulations

Is there any efficient method to access and change image pixels than the usual scanning the pixel array and changing them? I've a psuedocode but I want a a better method than this. I just need an algorithm, any language is fine. It looks something like this:-

   For i in range(0,len(pixel_array),4)
       pixel_array[0] = a   //a is some random value
       pixel_array[1] = a
       pixel_array[2] = a
       pixel_array[3] = 1