imgSweep

 Create a sweep frequency image as a test pattern.

     img  = imgSweep(imSize,maxFreq)

 The frequency increases across the columns; the contrast is high at the
 top row and decreases down the rows. Used by sceneWindow. 
  
Example:
  img  = imgSweep(256,16);  imagesc(img); colormap(gray); axis image
  img =  imgSweep;  imagesc(img); colormap(gray); axis image
  
 Copyright ImagEval Consultants, LLC, 2005.