title: Fastest way to convert an unsigned char image to a float image on iPhone
body: <p>I need to convert an unsigned char image (640x480x1) or smaller to a float image for processing. I can't do fixed-point computation in this case due to the problem complexity. I currently use the neon unit in a two-step process. The neon can convert an integer to an float fairly fast, but not an unsigned char to float.</p>
  
  <p>1) convert unsigned char image to integer image using a LUT (no generic casting since I know the range)
  2) use the neon to convert from integer to float</p>
  
  <p>This process take roughly 10-15 ms just to prepare the image for processing.</p>
  
  <p>I could also use a LUT in step one that converts directly to a float. However, I have found that doing this takes longer than using the NEON from integer to float. So I'd actually like to use the NEON to convert directly from an unsigned char to float and get rid of step 1.</p>
  
  <p>Does anyone know of a better way?</p>