The following tools can all be used directly to edit your image but the best way to use them is via Adjustment layers. These allow you to adjust your image without changing any pixels. A new layer – an adjustment layer – is created immediately above the active layer. Changes made with any of the adjustment tools will be applied to the layer(s) below. This is one way to achieve non-destructive editing, a key Photoshop concept.
Non-Destructive Editing
When you make adjustments directly to an image layer, this will change the pixels in that layer and information is lost. This information cannot be retrieved and it will reduce the quality of your image if you process further. Non-Destructive Editing is an approach to editing which avoids changing pixels wherever possible. This also means that you are always able to step back to a good version of your image if something goes terribly wrong. In effect, it means that any changes you make can be undone or edited further at any point in the editing process. Using adjustment layers is one way in which you can make adjustments without changing pixels directly.
Adjustment Layer Tools
The tools we’ll look at are in bold red text:
- Brightness/Contrast
- Levels
- Curves
- Exposure
- Vibrance
- Hue/Saturation
- Colour Balance
- Black and White
- Photo Filter
- Channel Mixer
- Colour Lookup
- Invert
- Posterise
- Threshold
- Selective Colour
- Gradient Map
Using Adjustment Tools
- Open the Layers panel. Click on the layer you wish to adjust. For now, this will probably be the Background layer.
- Open the Adjustments panel
- Click one of the adjustment tools. (If you hover over the icons, a tooltip will tell you what each adjustment is.)
- A new Adjustment layer will be created just above the layer you selected.
- The Properties panel will open. This is where you make adjustments.
As an alternative to Steps 2 and 3 above, click the Adjustment Layer icon at the bottom of the Layer Panel and select from the dropdown. 
One huge advantage of using adjustment layers is that you can revisit any adjustment layer’s properties and change the settings at any time. Just select the relevant adjustment layer and open the Properties panel.
The Property panel can be opened in two ways:
- Select the Adjustment Icon in the relevant layer. Make sure you haven’t selected the white rectangle icon. Then open the Properties panel.
The Adjustment Icon
- Double-click on the Adjustment icon.
In the examples in this section, the adjustments are being applied applied to entire layers. Later in the course we will see how adjustments can be applied to separate layers which target specific areas of your image. This is a much more effective way to use most of the adjustment tools. Don’t worry if you’re unsure about what layers are at this point. They are one of Photoshop’s most powerful features and we’ll devote a lot more time to them in due course.
Generic Options
Several options are available with every adjustment layer tool. These are found at the bottom of each tool’s Properties window.
Clip to Layer: Adjustment layers affect any layer which is lower down the layer stack. However, it is possible to ‘clip’ an adjustment layer so that it only affects the layer which is immediately below the adjustment. Move the adjustment layer so it is immediately above the layer you want to clip it to. Click the ‘Clip to Layer’ icon to clip. Click it again to remove the clipping.
View Previous State: Click and hold on this icon to compare with the previous adjustment.
Reset: Resets the adjustment to its default values.
Visibility On/Off: Turns the adjustment layer on or off.
Delete: Deletes the adjustment layer.