at all three of the auto commands

that reside here in the Image menu,

Auto Tone, Auto Contrast, and then Auto Color.

All three of which look at the luminance data

on a channel-by-channel basis

and make changes automatically

without even bringing up a dialogue box.

Now even though they sometimes work,

I am by no means suggesting

that they are the best ways

to adjust luminance data inside Photoshop,

but they might be the most popular.

Based on Adobe's analytics data,

they're click data from people who buy into the program.

Auto Tone, Auto Contrast, and Auto Color

together rank among the top 10 most commonly

used features in the software

in which case I want you to know how they work.

So here we are looking at some old school $100 bills.

And if you've seen my course before,

then you've seen this sample file.

It just happens to be the best demonstration

I've come up with.

And so we've got this top left bill,

which is our control image.

That is to say the one that we're not going to change.

And then we've got one layer each

for Auto Tone, Auto Contrast, and Auto Color.

I'm going to zoom in on the Auto Tone layer

by Alt or Option clicking on its thumbnail.

And then I'll just zoom out ever so slightly

by pressing Ctrl + minus or Command + minus.

And then with that layer selected,

I'll go up to the Image menu

and choose the Auto Tone command.

Now what this command does is it finds the darkest pixel

on a channel-by-channel basis

and changes it to black

and then it finds the brightest channel

on a channel-by-channel and changes it to white.

So in other words, it makes different modifications

for each of the red, green, and blue channels.

And as a result, not only do we increase the contrast.

So this is before and this is after.

But we also get rid of that green color cast

that is by nature associated

with an old school $100 bill

and we create a kind of reddish color cast in the shadows.

So Auto Tone can be really useful

if you're trying to get rid of a color cast.

But if you like the coloring of an image,

it's going to very likely mess it up.

All right, let's compare that to Auto Contrast.

I'll go ahead and Alt or Option click on that layer

and scoot it down just a little bit here.

Make sure the layer is selected.

And then I'll go up to the Image menu

and choose Auto Contrast.

Now this command also looks at the darkest pixel

and the brightest pixel in the image,

but it does so on a composite basis.

So in other words, it doesn't go channel-by-channel.

So it just finds the darkest pixel makes it darker,

the brightest pixel and makes it brighter.

And as a result, we maintain the green color cast.

So notice, this is the low contrast version of the bill

and this is a high contrast version.

We do have more contrast,

so darker shadows and brighter highlights

but we have the exact same greenish color cast

as we did in the past.

All right, compare this to the most complicated

of the auto functions, which is Auto Color.

Go ahead and Alt or Option,

click on that guy in order to zoom in on it.

Make sure it's selected as well.

And then go up to the Image menu and choose Auto Color.

Now before I choose it, let me explain how it works.

It's going to take the darkest pixel

on a channel-by-channel basis

and make it black and neutralize it as well

so that it doesn't have a color cast.

It's going to do the same thing to the brightest pixel

channel-by-channel and neutralize it.

And then it's going to try to find an exact midtone

and make it neutral as well.

And when I say neutral

I mean leach the color out of it, so that it's gray.

And so notice, as soon as I choose the command,

I am seeing dark neutral shadows

as well as bright neutral highlights.

And so the only colors that are surviving

even in the midtones are these very saturated greens.

And so if I were to zoom out

by pressing Ctrl + zero or Command + zero on the Mac

so that we can take in all of the bills,

you can see that Auto Contrast

is the one that's going to maintain the colors

inside of the image.

Auto Tone is going to remove any color cast,

but very likely replace it with a different color cast

in the case of these red shadows.

And Auto Color is going to do its best

to neutralize the shadows, highlights,

and midtones inside your images.

All right, so in the case of this $100 bill,

Auto Contrast probably does the best job.

In the case of an actual photographic image, you never know.

Now the first step in correcting the color cast

or if you prefer color bias of a photograph

is to identify what that color cast or color bias is.

And so here we are looking at an underwater GoPro photo.

No lights whatsoever.

Your photos don't have to be underwater.

I just happen to have a lot of them.

And so we can safely assume that this guy is too green.

After all, I'm about 30 to 40 feet deep

and so I've lost a lot of the color spectrum.

You lose the reds first, then the oranges, then yellows

and after a while, you're left with greens and blues.

But we are seeing a little orange here and there.

And even if we're pretty confident this is a greenish cast,

there's no sense in not checking for sure.

And you can check exactly what the color cast is

using the Eyedropper tool

which you can get by pressing the I key.

And one I've done is I've created

a bunch of copies of this layer

for comparative purposes later on.

But I also up here at the top have this shape layer,

which is a circle, which is identifying the region

that I think ought to be neutral.

And when I see neutral, it should be a lightish gray.

Whereas if I were to click inside there

and notice when I click and hold, I am seeing a color ring

which is showing me the old foreground color on the bottom

and the new foreground color at the top.

We can plainly see that that is a kind of green.

All right, but to confirm for sure

what we need to do is make sure

the color panel is on screen.

And if it's not, you can go to the Window menu

and choose the Color command.

Of course, do not choose the command

if it has a check mark in front of it,

and then click on the flyout menu icon

in the top right corner

and switch to HSB Sliders

is generally the easiest way to work.

And that way we can see our hue, saturation,

and brightness values.

Now all the brightness value is doing is telling us

that this is a pretty bright color,

so it's somewhere in the mid tone to highlight range.

That's just fine.

It's not anything we need to worry about.

The hue value is telling us the base color in degrees

and I'll show you what that looks like in just a moment.

And then the saturation value goes from gray at 0%

all the way to the most highly saturated version

of that specific color at 100%.

Now if this were a neutral image,

if it didn't have a color cast,

then this saturation value

would be somewhere in the zero to 10% range.

Instead, it's extremely high at 37%.

That means we have a pronounced color cast.

All right, let's take a look at the hue value, however.

172 degrees is very close to cyan.

And so I'll go ahead and switch over

to this big color chart that I've created for you.

And by the way, it measures 32 by 22 inches

in case you decide you want to print it out.

And I've gone ahead and mapped out