Alright, so what I am going to do, let's now do something a little more real world here than that, less demonstrational, more corrective. I am going to choose the Revert command from the File Menu or press the F12 key in order to switch back to the original version of the image that I know is actually in really great shape. It is the 8-bit per channel version of the image though. So I am going to press Shift+F4 assuming that I have my keyboard shortcuts loaded, if not, you go to the Image Menu, choose Mode and then choose 16-bit per channel and you will see 16 next to RGB here in the Title Bar.

Now let's say that this image is supercritical, it's very, very critical to you that you get the colors exactly right, because this is the only time -- this is your daughter and this is the only time she is going to get married, darn it, you want to do this precisely correctly. Well, then before you enter the Levels dialog box you might want to identify exactly where the lightest and darkest colors inside the image are, and I am going to do that with the help of a couple of adjustment layers here.

First I am going to go over to the Layers Palette and I am going to increase the size of the thumbnails inside the Layers Palette by right-clicking in this empty area, or if you don't have a right-mouse button on the Mac you need to press the Ctrl key and click, or drive to the store and get a mouse that has a right mouse button. And I am going to change these thumbnails to large thumbnails. Inside this pop-up menu here, we have nice, big thumbnails inside the Layers Palette. I am also going to press the F key once so that I can enter this Full Screen Mode and I am going to scroll the image over just a little bit here, because I have a sneaking suspicion that the lightest colors inside the image are in the upper left-hand corner of the photograph, but to make sure to see exactly where those colors reside. I am going to go down to this little Adjustment Layer icon, down at the bottom of the Layers Palette. I am going to click on it and I am going to choose Threshold.

Now the Threshold command is great, it's not really a color correction command, it's a posterization command, sort of a special effects command, semi-useful for masking sometimes, really great though for gaging an image and because this is an adjustment layer, I am not actually applying it to the image itself, I am just having it hover on top of the image. I am going to move this Slider over to the right-hand side until I have just as little white as possible, see that? Sort of about 242 I just have this tiny blob of white up here -- in the upper left-hand corner of the image. I am going to go ahead and zoom in on the image, which I can do, even though the Threshold dialog box is visible on screen by Command+Spacebar or Ctrl+Spacebar clicking inside the image. I am going to increase this value just nudge it upwards by pressing the Up Arrow key and what I want to do is keep nudging this value upward until this little area disappears, there, it goes away.

So I am going to nudge it back downwards so I can identify that this is where the brightest pixels reside. There they are in this little sort of L shape right there and then I'll click OK. This helps me identify where those light values are located. I am going to zoom in some more into this image so I can see exactly where those pixels reside and now I am going to permanently identify that portion of the image, by going over to the Eyedropper Tool and choosing the Color Sample Tool and I will click somewhere inside this L.

Now I don't really like the appearance of the Eyedropper cursor because it's tough to tell where the hot spot is, exactly where you're going to set this Eyedropper location, this Eyedropper target. So I am going to press the Caps Lock key in order to switch to the precision version of the cursor which just appears as this little tiny cross here and I am going to click in an area that I see that's obviously white in order to set my color target. You can see that it's tiny little target right there at this point.

Now the great thing about these color targets is they not only stay in place inside of an image, they get saved along with an image. So if you save this image and close it, you will save this color target as part of the image, it's not a printing object obviously, it's just little guide and it's tracked inside the Info Palette. So make sure that you have your Info Palette on screen, press F8 if not, and you'll see number one RGB, these are the RGB values, 255, 255, 255, so this is a white pixel, but it's only a white pixel because of the threshold that's been applied to it, so I am going to turn off the Threshold layer. You can keep it inside the image. You can even throw it away if you want to, but I am going to keep it inside the image. I am going to switch back to the background and we'll see that the brightness of this pixel is actually 243, 243, 243.

But we know because we applied this Threshold Adjustment Layer that that is indeed the brightest pixel inside the image. We don't need the Threshold layer anymore, we can just keep this color target. It's doing all the work that we needed to do. Alright, now I am going to turn on -- strangely enough, I am going to turn on the Threshold layer once again and I am going to zoom out from the image and I am going to scroll down to the lower right-hand portion of the image, down here where we see the difference between black and gray here, gray is outside the image. I am going to double-click on this Layer Thumbnail here, on the actual thumbnail, not the white portion, that's Layer Mask, double-click on a thumbnail, to bring up the Threshold dialog box once again, and now let's find the darkest color inside the image, and I am going to do that by reducing the Threshold value until I just see a speck of black somewhere inside the image.

It looks like this is little speck of black right there and there is another speck of black up here. So there is one speck, there is the other speck. If I lower the value by pressing the Down Arrow key, this speck goes away, but this speck stays here and I expect that that speck is as small as I am going to get things. So that really represents the darkest color inside the image. So I'll go ahead and click OK in order to accept that change, I'll zoom in and off a lot I still have my Color Sample Tool active here. And once again I'll click, still got the Caps Lock key down, I'll click in order to set the location of color target number 2, you should be able to see a little tiny 2 next to that target and you'll see a 2 with RGB over here inside the Info palette. If you want to move that, if you want to adjust the placement of one of these guys just a little bit, you can drag it, okay, so you can drag it from one pixel to another pixel if you like.

Clicking creates a new target. You can have up to four targets, dragging moves the targets around and to delete a target, you press the Option key or the Alt key and hover your cursor over the target and you get this little pair of scissors. Then you click and it deletes the target. I want you to do that. I want you to have two targets. So it's telling us that 0, 0, 0 is the brightness value of this target, keep in mind that that is subject to this Threshold value. I am going to turn off Threshold, I am going to go to the Background layer, it's a brightness of 36, 33, 24; 36 in the red channel, 33 in green, 24 in blue, and so what that means is that's actually a relatively light shadow but that's as dark as the shadows get inside this image, that's why it appears slightly washed out and turns out that this darkness, this darkest portion of the image is right there inside of this girl's mouth. So there is the darkest pixel, we scroll up a little bit and we find the lightest pixel up here. So we now know where the lightest and darkest pixels inside the image are.