Is there a way to increase/average the number of pixels that the black/grey/white picker sub-tool samples in the levels tool?

The question behind the question. I'm using a QPcard (black/18% grey/white) target when I take digital images to make fixing contrast and white balance easier. What I'm noticing is that none of the three targets are consistant in the RGB values across the target patch (according to the info window). I suspect that camera sensor noise is responsible. So while any given pixel might have a range of RGB values, a group of pixels (from one of the targets) should average close to the correct value. I noticed the color picker tool can be set to have a radius and average. Did I miss how to do this for the levels tool?

BTW, the QPcard (according to competitor WhitBal) is about as accurate as a Kodak Q13 target for the w/g/b values and reflective spectral responses. I also have a Q13 target that yields similar results. I can post example tiff or jpgs.

Jim F.
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