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Layers and Layer Masks – Part 2

Non-destructive Image Editing in Photoshop

Layers & Layer Masks – Part 2


In Part 1 the basic concept of Non-destructive Image Editing using Adjustment Layers and Layer Masks was outlined. In this article we shall look further at Adjustment Layers and at other non-destructive editing techniques using Layer Masks .


Gradient Masks

Gradient masks are a handy tool to use where a gradual change in tone from 0 – 100% is required over, say, a sky to make it darker at the top or a foreground to make it darker at the base. Painting on a Layer Mask with the softest of brushes is rarely a satisfactory solution in these cases.

To create a Gradient Mask to darken a sky select the Gradient tool from the Toolbox and ensure that the Linear Gradient black to white is selected in the Gradient Picker dropdown (Fig 1).


Fig 1  Gradient Picker


Enter Quickmask mode by pressing Q on the keyboard. Position the cursor at roughly the point at which you want the graduation to end, hold down the Shift key and with the left mouse button depressed move the cursor to the top of the image and release the mouse. A graduated Quickmask is overlaid on the image (Fig 2). Exit Quickmask Mode by pressing the Q key and a selection appears on the image outlined by marching ants (Fig 3). If the selection is not sized to your liking it can be changed by Selection > Transform Selection; the selected area will be surrounded by a bounding box with ‘handles’ at each corner and at the mid point of each side. Click and drag the handles until the selection meets your needs – then press Enter to complete the transformation. If the area selected is the opposite to that intended inverse the selection -  Select > Inverse.

With the selection active apply a Levels Adjustment Layer. (Note that whenever a selection is active on an image an Adjustment Layer can be applied affecting only the selected area and the remaining area is automatically masked out by the Layer Mask). Adjust the levels dialogue to suit (Result in Fig 4) and click on OK. The Layer Mask icon on the Levels Adjustment Layer in the Layers Palette will show the gradient mask created – this is shown image size in Fig 5.



Fig 2  Graduated Quickmask


Fig 3  Gradient Selection



 Fig 4  Effect of Gradient Adjustment


Fig 5  Detail of Gradient Mask


Gradient Masks are not limited to the orientation shown and can be applied at an angle to adjust a corner or vertically to adjust a side. Only hold down the Shift key when you want the base of the gradient to be parallel to the top or one side of the image.


Clipping Groups

Any number of Adjustment Layers may be applied to an image – the physical limit of 7,000 is unlikely to bother anyone! Each Adjustment Layer affects all the other layers below it and is clearly not a problem where there is only a single image layer. However in an image which contains 2 or more image layers, e.g. a landscape in which the sky has been replaced and there are separate images for the sky and foreground problems will arise unless the necessary action, outlined below, is followed. Let us assume that the Sky Image Layer is below that of the Foreground as shown in Fig 6.

If we apply an Adjustment Layer for, say Levels, at the top of the stack of layers any adjustments made on the Levels layer will affect both image layers (Fig 7).



Fig 6  Two Image Layers – Levels Adjustment Layer added.


Fig 7 Effect of Levels Layer – both images are affected.


 If the Levels Adjustment Layer is clipped to the image layer immediately beneath it only that layer is affected by the Levels adjustment (Figs 8,9)


Fig 8  Levels Adjustment Layer clipped to top Image Layer.

Fig 9 Effect of Levels Layer after clipping – only the foreground is affected.


To clip an Adjustment Layer to an Image Layer position the cursor at the common boundary between the two layers where it will change to a hand icon. Hold down the Alt key and the hand icon changes to two circles one of which is filled with black. Left click with the mouse and the two layers will be clipped together as shown by the arrow highlighted in Fig 8. Any adjustment of the Levels Layer will now only affect the Image Layer to which it is clipped, in this example Boathouses. Multiple layers can be clipped in this way (Fig 10). To unclip a layer repeat the procedure outlined above.

In the Layers Palette show in Fig 10 Levels 1 and Black & White 1 are clipped to the Boathouses image and affect only that image. Levels 2 and Channel Mixer 1 affect only the Sky image and as there are no other Image Layers beneath the Sky do not need to be clipped. Note: When converting a multiple image to monochrome it is sometimes better to use a different conversion method on each image.




Fig 10  Layers Palette for multiple Image and Adjustment Layers.

Fig 11  The effect of the Adjustment Layers shown in Fig 10.




Adjusting the Effect of Adjustment Layers

The effect of an Adjustment Layer on the Image Layer beneath can be changed in one of two ways – Opacity and Blending Mode

The strength of the adjustments made on an Adjustment Layer may be reduced by altering the Opacity of the layer – if the opacity of the Adjustment Layer is set at 50% the effect of the adjustments made on that layer and visible on the Image will be reduced accordingly. To adjust the Opacity click on the dropdown arrow adjacent to the Opacity box – default setting 100% and move the slider to the left to reduce the opacity. Alternatively in later versions of Photoshop positioning the cursor over the word Opacity causes the cursor arrow to change to a hand with left/right arrows; hold down the left mouse button and drag the mouse left or right to decrease or increase the Opacity.

The way in which the effect of an Adjustment Layer is applied to the underlying image is controlled by the Blending Mode – Normal is the default. Blending Modes are outside the scope of this article, but feel free to try the different modes on offer in the dropdown list adjacent to Normal. For example to increase contrast further in Levels try the Soft Light blending mode and to eliminate or minimise colour changes when applying Levels to a colour image try Luminosity mode.

In the final part of this article we shall look at ways of using Image Layers as pseudo Adjustment Layers.


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