Why are the values different? |
According to Adobe employee Simon Chen (Auto Tone of a batch of photos gives different results than if you do them one at a time | Photoshop Family Customer Com…):
This is what happens, when the Auto button is activated, it means Lr has loaded the full resolution negative. So the Auto is computed based on this full resolution negative. When you apply Auto to a batch of photos, for performance reasons, Lightroom loads a lower resolution negatives cached in the camera raw cache (like Smart Previews) and computes Auto from that. Since the two input are different, the results could differ slightly. |
Most of the time, the differences between batch and individual application of Auto are very small and hard for a human to notice, e.g Exposure of -0.31 versus -0.36. But sometimes the differences can be quite noticeable, as I observed in that same topic.
If you have examples where the differences are visually noticeable, please upload the masters to Dropbox or similar and post the sharing link in that bug report. Adobe appears to believe that the differences are very minor, so unless users post counter-examples, they'll continue believing that.