5a Mask Layer
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Masks can be a fun and relatively quick way to create photo composites, and even provide an effects-like look to images. Having said that, most of the affects that can be achieved using masks can be achieved in other ways too - the advantage of using a mask layer is that you can come back to it any time to make adjustments whereas making adjustments to what you have done using other methods may be much more difficult or impossible. In this lesson, to emphasise that using mask layers often just provides an alternate method of doing things you already know how to do, I will show you how you can do two exercises that we have already done, but this time using mask layers. YOU CAN SKIP THIS LESSON IF YOU LIKE OR IF YOU BELIEVE THAT YOU ARE LAGGING BEHIND MOST OF YOUR CLASSMATES.

The lesson below is an excerpt from the Paint Shop Pro learning centre which you can access from Paint Shop Pro at any time by choosing Help > Learning Centre or pressing F10.

Using Mask Layers - Basic

Step 1 - Display Layers palette, open two photos

If it isn't already displayed, display the Layers palette. Now open two photos, ideally photos of the same size or scale, and one of which has an element that would look somewhat natural if placed in the second photo. For example, open two photos containing people, or one with people and one with a landscape.

Step 2 - Copy one photo to the clipboard

Decide which photo contains an element that you'd like to combine with the other, and make this first photo the active one. Now copy all of the photo (by pressing Ctrl+C, or choose Edit > Copy) or just the desired part of the photo (by using one of the selection tools -- you don't have to be precise) to the clipboard.

Step 3 - Paste into the second photo

Make the second photo active, and then press Ctrl + L, or choose Edit > Paste > Paste as New Layer. Notice in the Layers palette that this is now the active layer. If necessary, use the Move tool to position the layer as desired.

Step 4 - Create the Mask Layer

With this new raster layer active, choose Layers > New Mask Layer > Show All. As you can see in the Layers palette, this creates a Mask Layer grouped with the new raster layer. Notice that the Mask Layer is now the active layer.

Step 5 - Choose the Paint Brush tool

From the Tool toolbar, choose the Paint Brush tool.

Step 6 - Set colours in the Materials palette

In the Materials palette, set the Foreground/Stroke style to the colour option, and then set the foreground colour to pure Black. Likewise, set the Background/Fill style to the colour option, and then set the background colour to pure White. (Masks work by hiding all pixels painted Black, and conversely showing pixels painted White.)

Step 7 - Paint on unwanted image area

Place the Paint Brush cursor over pixels you want to hide, hold down the left mouse button (to paint with Black), and then paint with slow, careful strokes to hide these pixels, revealing the image below. (If necessary, adjust the brush's Size setting larger or smaller as needed.) Continue doing this until you've isolated the desired image element, making it appear as though it was part of the underlying photo. If you mistakenly remove part of the desired image element, simply paint over the affected area with the right mouse button (to paint with White), restoring pixels.

Notes and Tips:

bulletRefer to the Help system or the User Guide for more information on masks.
 
bulletTry choosing Layers > Load/Save Mask > Load Mask from Disk, and then select one of the sample masks that come with Paint Shop Pro.
 
bulletBe aware that you can adjust the brush size via the keyboard. Refer to the Help system or the User Guide for details.

Using Mask Layers - Intermediate

When you are working with the selection tools, you can easily get the impression that selections have hard edges i.e. every pixel is either inside the selection or out of it. But when you read about feathering and anti-aliasing you may have realized that this is not so - it is possible for some pixels to be 'partially selected' so that effects applied to the image are applied to these pixels only to a limited extent. Paint Shop Pro has a feature called Edit Selection which you learnt about in lesson 4d. Paint Shop Pro also allows you to put a Mask Layer on top of an image so that the mask layer determines which part of that image will be affected by changes that you make.

To get some practice with mask layers, let's use the picture below. I took it in Thailand on a canoeing trip with students of the Hong Kong International School. The stilt house is occupied by a family that farms collects swallows' nests from the caves of this island. Swallows' nests, made from the birds' saliva, are an expensive delicacy in many Asian countries.

Although the picture is already pretty good (I took it myself, after all), we'll try to give it a surreal feel as in the photo below. We want to apply a strong affect to the top of the picture, gradually weakening towards the bottom.

The basic approach we will use is this:

  1. Put the photo into the background layer - let's call this 'layer A'.
     

  2. Duplicate the layer to create a new layer which is a copy of the background layer. This new layer is on top of the background layer - let's call the new layer 'layer B'.
     

  3. Create a mask layer (layer C) on top layer B. The mask layer will contain a greyscale pattern (black, white and shades of grey). Where the mask layer is black, the layer underneath it (layer B) will be transparent, exposing layer A. Where the mask layer is white, the layer underneath it (layer B) will be opaque, hiding layer A. Where the mask layer is grey, the layer underneath it (layer B) will be partially transparent, so layers A and B will be superimposed. exposing layer A.
     

  4. We will place a pattern into the mask layer which is a gradient, going from white at the top of the layer to black at the bottom. This means the top part of layer B will be opaque while the bottom part will be transparent.
     

  5. We will colourise the masked layer, layer B, with the purple hue you see above. Colourising a photo does not change the black or white parts of the image but all other parts take shades of the chosen hue (purple). Because of the masking of layer B we will only see the colourising effect in the top part of the finished image. Since the bottom part of layer B is transparent we will see the original, non-colourised photo in the lower half.

Now here are the steps in detail:

  1. Copy the top picture above and paste it into Paint Shop Pro - it will appear as the background layer (called background) of a new image. Make sure that the layers palette is visible (press F8 if necessary) so that you can see the background layer (you can even point at it if you like to see a thumbnail image of that layer).
     

  2. Choose Layers > Duplicate. In the layers palette you will see that you now have a new layer called 'Copy of Background' on top of the background layer.
     

  3. Now choose Layers > New Mask Layer > Show All or, in the layers palette, click the 'Mask Show All' button . In the layers palette you will see you have just created a new mask layer called 'Mask - Copy of Background' which is above the 'Copy of background' layer and grouped with that layer. Pointing at the mask layer in the layers palette shows you that the layer is a uniform white, indicating that the masked layer under it is is opaque and therefore visible (hence the phrase 'Show All').
     

  4. Now for the trickiest step: setting up and applying the gradient to the mask layer. Switch the 'colour' option (pointed to in this picture) to 'gradient' then click the 'foreground and stroke properties rectangle' (the big black rectangle in the this image). This will open the Material Properties dialogue - make sure the gradient tab is selected, and that 'black and white' gradient is selected with angle=0, repeats=0, style=linear, then click the 'edit' button. Set up the gradient and transparency as follows:
                         
    I have placed markers on the gradient line as follows:
      - at location 0% there is a marker set to pure black (drag an existing marker here, or create a new one by clicking, and then click the 'fore' button to copy the foreground colour to the selected marker. Note that if you want to delete a marker you can just drag it away form the line).
      - at location 61% there is a marker with a 'custom' colour set to Red=79, Green=79, Blue=79. This combination is a medium grey. You can set a custom colour for the selected marker by clicking the big rectangle next to the word 'custom'.
      - at location 100% there is a marker set to pure white (drag an existing marker here, or create a new one by clicking, and then click the 'back' button to copy the background colour to the selected marker.

    The transparency line is set to 100% opaque (same as 0% transparent everywhere) on the gradient.

    Now exit the dialogue, saving the new settings for the black and white gradient. Make sure that when you point at the mask layer in the layers palette you see a thumbnail image of the mask like this: . Make sure the mask layer is selected in the layers palette then choose the Flood Fill tool and click anywhere on the image to apply the gradient. You won't see any difference on the image since the two layers under the mask are identical so it makes no difference yet whether the mask makes the masked layer transparent or not.
     

  5. Now we want to colourise the layer called 'Copy of Background' to get the purple hue for the sky but we have a problem: the sky is mainly white and colourising has no effect on white areas. Therefore as a preliminary step we must darken this layer. In the layers palette, select the layer called 'Copy of Background' then darken it with Adjust > Brightness and Contrast > Brightness/Contrast. Set the brightness to -73 (minus 73) and notice how the darkening applies mainly to the sky rather than the water due to the affect of the mask we have set up.

    Now we are ready to colourise this layer. Then choose Adjust > Hue and Saturation > Colourise. Try different settings for hue and saturation, then try to get an effect like mine by using hue=205 and saturation=207. And now you're done! Note that the procedure is easier in Photoshop than in Paint Shop Pro because Photoshop has a useful 'Quick Mask' mode which Paint Shop Pro lacks.

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