Auto Tone, Auto Contrast and Auto Color operate off of Photoshop algorithms that asses your image and from that assessment, Photoshop applies what it has determined is “right” for the image.
This is Destructive editing done under the hood and isn't visible to the user. That being said you can achieve Non-Destructive editing by using adjustment layers.
There's no actual Auto Tone, Auto Contrast or Auto Color adjustment layer. Instead, the commands are made available to us as options in other adjustment layers, namely Levels and Curves
- Add a Levels adjustment layer by clicking on the New Fill or Adjustment Layer icon at the bottom of the Layers panel:
- Click the small menu icon in the top right corner of the Properties panel to access the Auto commands:
- The Algorithms section at the top has four different options to choose from. Focus on the top three (Enhance Monochromatic Contrast, Enhance Per Channel Contrast, and Find Dark & Light Colors). They are the ones that correspond to the three Auto image commands:
- The first option at the top, Enhance Monochromatic Contrast, describes how the Auto Contrast command works. Choosing this option will give you the same result as if you had selected the static Auto Contrast command from under the Image menu.
If you can't remember the details of how each Auto command works but you have Tool Tips enabled in Photoshop's Preferences, there's an easy way to tell which of these options corresponds to which Auto command. Simply hover your mouse cursor over the name of an option to see a more detailed description of it. Notice that at the very end of the description, it actually says which Auto command it matches. In the case of this first option, Enhance Monochromatic Contrast, it shows Auto Contrast in parenthesis:
- The second option from the top, Enhance Per Channel Contrast, is the same as the Auto Tone command.
If you hover your mouse cursor over the Enhance Per Channel Contrast option to view a more detailed description of it, you can see at the end that it lists Auto Tone in parenthesis:
- The third option, Find Dark & Light Colors, is the same as the Auto Color command, which also darkens the darkest pixels to black, lightens the lightest pixels to white, and redistributes the other tonal values in between on a channel-by-channel basis, just like Auto Tone.
Hovering over the Find Dark & Light Colors option to view the description, and you can see Auto Color listed at the end:
There's one extra step here to recreating the same effect as Auto Color. In order to neutralize the midtones, you also need to turn on the Snap Neutral Midtones option by clicking inside its checkbox. Again, if you hover your mouse cursor over the option to view the description, you'll see that it lists Auto Color at the end:
- One really great benefit of applying the Auto commands this way, rather than as static adjustments, is that you can actually combine the Snap Neutral Midtones option with any of the Auto commands, not just Auto Color.
For example you can leave Snap Neutral Midtones selected, but switch from the Find Dark & Light Colors option to the Enhance Per Channel Contrast option, effectively combining the Auto Color and Auto Tone commands:
Always, always, always perform your edits in a non-destructive manner. This allows you to not only make minor tweaks and edits independent of other variables but also allows you greater control with layer masks.