<blockquote>
<p>my action will downgrade the original file to this size in 10 steps.<br>
by doing so you ensure the processing algorithms of jpg's compression layers to run over it more often and thus<br />have more detail remaining than just buy running it once.</p>
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With all due respect, this is a load of nonsense. First, understand that reducing the pixel dimensions of an image does not in any way involve the jpeg algorithm. The jpeg compression is only invoked when you save the file out of Photoshop (or Lightroom etc.) as a .jpg. Second, multiple applications of the jpeg algorithm will <strong>reduce</strong> the amount of detail in your file (sometimes severely, depending on the level of compression you choose), not preserve it, as you appear to be proposing.
C