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Old September 13th, 2007, 04:46 AM
Tim Armes Tim Armes is offline
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Join Date: Jun 2006
Location: Drôme, France
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Default TIPS & TRICKS No. 7 - Adjustment Layers

This thread is part of the Tips & Tricks problematics. See here for more information.

Hi all,

With this thread I'd like to try to introduce Photoshop's adjustment layers to the uninitiated. Adjustment layers are essential to good photographic retouching skills, and I feel that even beginners should learn how and why we use them before bad skills get en-grained.

Most resources follow the logic of teaching layers first, then masks, and then adjustment layers. This is a reasonable approach, however, as we'll see, for photographers the adjustment layers are more important than normal layers, and by leaving them until last the learner is often suffering from information overload by the time the important stuff gets explained.

I'm going to take a different approach. I'm going to move right along to the stuff that we find really useful, and let normal layers fall right into place in their own time.

I'll leave the thread open for questions, however I'll probably update this post with more information if I feel that it's necessary. This will ensure that the tutorial information is easy to find.

THE WHY

The bane of my life when I teach Photoshop is the Image->Adjustments menu. Most self learners discover this menu by themselves, and the proceed to use it without further consideration; this is very unfortunate. Follow along with the following to understand the problem:

1) Open up a picture
2) Choose Image->Adjustments->Levels
3) Move the black slider to the right for a dark image, and click OK.
4) Choose Image->Adjustments->Hue/Saturation
5) Add a little saturation, and click OK.

Now imagine that you decide that your levels adjustment wasn't quite right it's way too dark. How are you going to change it without altering the work that you've done since then (in this case, changing the saturation)?

You could try doing another levels adjustment, but it's too late - you've already lost all your shadow detail. The only solution is to undo to that point (if you can go back that far), redo your change and then redo all your work. This is because the change that you made was destructive - it's actually changes the values of your pixels.

Adjustment layers solve this problem by allowing you to do non-destructive editing. As a further bonus, they also allow you to apply your adjustment to just part of the image, rather than the whole thing. Let's take a look:

THE HOW

Most of the adjustments found in the Image->Adjustments menu can be achieved using an adjustment layer. The best way to understand them is to create a couple. Follow me along with this:

1) Open up the image that you had opened previously
2) Ensure that the layers palette is open (Windows->Layers should have a tick next to it)
3) At the bottom of the layers palette, click the black and white circle (see image below), and choose "Levels" from the menu. This will pop up the level dialog.
4) Move the black slider to the right for a dark image, and click OK.
5) Click the black and white circle again, and choose "Hue/Saturation" from the menu.
6) Add a little saturation, and click OK.

You've now created two adjustment layers that apply your desired changes to everything underneath them. The layers window should look like this:


The important thing to realise is that your base image hasn't been changed, the adjustments are placed "on top" of it. We can modify the adjustments at any time. For example, double click on the icon for the "Levels" adjustment layer that you've created, and you'll be able to change the settings. You can do the same for the Hue/Saturation layer. This is what we mean by "non-destructive" editing - your image hasn't been touched.

You can turn off each of the layers by clicking their associated eye icon. Click again to turn it back on. If you turn both layers off, you'll only see your original image, unchanged. You can delete a layer entirely by clicking on the layer to select it, and then clicking on the dustbin icon at the bottom of the palette.

MASKS

The true power of adjustment layers lie in the use of masks. You'll see that each layer has a little white square next to it - this is a reduced picture of its mask. The mask allows you to choose the parts of the image that the adjustment is applied to. Let's try:

1) Click in the white mask square of your "Levels" adjustment layer.
2) The double border around the square tells you that you're now working with that mask. Note that your foreground and background colours are now black and white. Masks can only contain shades of grey.
3) Choose a fairly big soft edged brush, and make sure that you're painting in black.
4) Paint over parts of your image.

Wherever you paint, the effect of your adjustment layer disappears! You can see a reduced version of the mask that you're creating in the layer's mask square. Where you paint in black, you conceal the effect of the adjustment layer. Paint in white to get it back again. By using a soft edged brush the edges of your strokes fade off through grey, which stops the effect from having obvious edges.

To help you, remember this mantra:

White reveals, black conceals


A CONCRETE EXAMPLE

Let's use this technique to apply a little dodging and burning to an image.

1) Open an image of your choice
2) Create a "Levels" adjustment layer, and move the center point to the right to darken the image. Click OK.
3) Double click on the name of the layer and rename it "Burn"
4) Click in the layer's mask square.

Since the mask is all white, the entire image is being darkened; this isn't what we want. We'd rather that the image remained unchanged and that we paint over the parts that we want to darken. In other words, we want the mask to start off black (concealed).

5) Choose Image->Adjustments->Invert

Since we've previously clicked on the mask, the inversion is applied to the mask, and the mask turns black.

6) Paint in white where you want to burn the image. If you make a mistake, simply paint in black. If the effect is too weak or too strong, open up the adjustment layer's dialog box and move the center point to taste.

7) Create a new "Levels" adjustment layer, and move the center point to the left to lighten the image. Click OK.
8) Double click on the name of the layer and rename it "Dodge"

Now repeat steps 4-6 on the new layer to lighten part of your image.

CONCLUSION

Adjustment layers allow you to apply adjustments non-destructively to the parts of the image that you want to change. They allow you to experiment and to make changes at any time, without worrying about destroying work that's already been done.

These techniques will give you a base upon which to build your Photoshop skills. Good use of Photoshop is based on layers. Starting with adjustment layers will allow you to make the sorts of modifications that you will want to do whilst building good Photoshop habits for the future.

We can do lots more with layers, but start with this and build up slowly.

Tim
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