Photoshop auto controls

[rogprov]

I can use Photoshop fairly competently and have been doing so for a couple of generations of the software. One aspect I’ve never really understood is what is Photoshop trying to do when the Auto levels/contrast/color tabs are used ... what’s going on under the hood? I rarely use them but have tried on occasions and the results can be really strange and way off what one would do manually ... particularly the auto-color can come up with some weird "corrections".

[KevinBarrett]

As near as I can figure, auto contrast treats all channels equally at the same time, and auto-levels threats each channel individually. What the treatment is, essentially, is stretching the curve so that the maximum and minimum values represented in the picture are now the maximum and minimum values available in the color space. It will clip off any outlying shadows or highlights that it deems insignificant to the picture.

If anyone has a better understanding of it than this, please clarify.