Making changes with Adjustment layers

Adjustment Layers

Adjustment layers are a great help in maintaining image quality.

It is better to understand some of the Photo shop tutorials on colour and tone changes (such as Curves and Hue/Saturation) before dealing with this tutorial.

When an image is modified with such functions as Curves, Levels, Selective Color and Hue/Saturation, the pixels are permanently modified and information will be thrown away.
A severe adjustment to contrast or colour can throw away quite a lot of digital information. If we go back later and make another change, more information will be lost.

A way round this is to use an Adjustment Layer. This is a form of screen above the layer which will show the effects of the changes without actually changing the layer's pixels.
An adjustment layer can be saved and modified again at another time and the original layer is still preserved. It is only when the image is flattened that the layer's pixels are finally modified.

Adjustment layers are extremely important in allowing re-editing and experiments and should be used as much as possible.

Download the PDF image file HERE and open image number 1.
The tone and colour of the image need correcting.
Press F7 to open the Layers palette.
At the bottom of the Layers palette is a line of small icons.
Click on the icon to Create new fill or adjustment layer.
From the pop-up menu choose Levels.
In the Levels dialogue box, move the central triangle to the left to 1.40, although the number required may vary on different monitors. This lightens the central tones of the image.
Still in the Levels dialogue box, from the Channels pop-up menu choose Blue.
Move the central triangle to the right to .74. This reduces the blue layer and removes the blue cast. OK.
For this function, Levels produces a similar result to Curves.
The Levels adjustment layer now appears in the Layers palette and is called Levels 1. It has its own separate layer and although the effect is there, the image itself has not yet been physically modified.
Another advantage with adjustment layers is that more than one can be used at the same time. We will use Selective Color to brighten up the grass.
A second method to create an adjustment layer is to go to Layer > New Adjustment Layer > Selective Color. This method provides the option of choosing a name for the layer, otherwise use the name which comes up and click OK.
For Method choose Absolute and under Colors choose Greens.
Green is the opposite of magenta so reduce the magenta setting to -23 which will increase the greens in the image. Note how the grass colour becomes richer. Click OK.
The Selective Color adjustment layer is now in the Layers palette.
The image can be saved in this state.
At any stage, a double-click on the large icon in the adjustment layer will open its dialogue box.
Further changes can then be made and saved.
Only when the image is flattened, saved and closed are the changes to the image layer made permanent.

An adjustment layer can be applied permanently to its layer.

In the example on the right, one would hold Shift and highlight the Levels layer with the Background.
Link the two by clicking on the Link icon at the bottom of the Layers palette.
Click on the arrow in the top right corner of the Layers palette and choose Merge Linked.
When an image like this is flattened, the adjustment layers are applied to the image from the bottom up. This can have a bearing on the order you have the adjustment layers in the Layers palette.

A standard adjustment layer will affect all layers beneath it. Very often, there are going to be several layers and we want the adjustment layer to affect one layer only. This can be done by clipping the two together.

Linking layers

• Move the cursor to the join between the adjustment layer and the normal layer below it. The hand symbol changes to a double circle with an arrow. Click.

• The adjustment layer moves to the right and now will only affect the layer directly below it.

• The clipping can be removed in the same manner.

Tip
Working on a high-res image can be very time consuming - we never seem to have enough RAM and processing power. A useful trick is to do all your experimenting on a low-res copy of the image. Any adjustment layers can be dragged across on to the high-res version.

Summary of Adjustment Layers

� An adjustment layer works like a preview on the layer without physically changing the normal layer.

� There is no material change or destruction to the normal layer until either the adjustment layer is merged with its layer or the image is flattened.

� They can be used for Curves, Levels, Selective Color, Channel Mixer and many other functions we have not covered yet.

� An adjustment layer can be modified as often as you like without damaging the pixels.

� The adjustment layer does not have to be at 100%; its strength can be lowered.

� An adjustment layer can affect every layer below it.

� An adjustment layer can be clipped to the layer below it, so that it works only on that layer.
When clipped to one layer, it will not affect other layers below it.
It can also be grouped with a set of layers.

� They can be saved and the file closed, then adjusted again at another time.

� Masks can be applied to adjustment layers. Masks come later, but they let you decide exactly what part of the normal layer will be affected by the adjustments.

The moral of the story is: "Use adjustment layers as often as possible".

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