linear gradient drawing inside an alpha mask

Gradients & Lines
Drawing with the linear gradient tool inside a linear selection mask to create lines of changing colors

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In this tutorial you'll learn some tools and tricks to use the line tool with a gradient to make it look like the line is changing color according to the gradient. This can be used for a variety of effects, such as the one here:

The Gradient Tool

If this is the first time you've used the Gradient tool, here's a refresher: you can open the gradient panel in PD Pro 4 from the Window menu:

Window > Gradient panel...

or use the keyboard shortcut 'p'

Perhaps it stands for 'p' is for 'pretty colors' or 'plentiful'?

The gradient tool offers 8 pre-loaded gradients. And there are others to choose from.

Select for example the default radient's first gradient, going from black to white through all grey values.

You will use the gradient later.

Painting on Alpha with pre-defined brushes

Let's now pick a brush which paints on alpha. Right-click on the brush tool icon (or middle-click on the main image buffer) to show the menu with the predefined brushes.

Look for "Paint on Alpha" type brushes, and select the Hard or the Soft brush.

Then draw a quick dab of a single brush stroke. In this example it's from upper-left to lower right. The background (and secondary) color is black, the primary color is white. The drawn brush stroke appears at primary color, at least initially.

So far we haven't released the mouse button yet:

But as soon as you let go and release the mouse button (or lift the pen if using a tablet), the result is transfered into the alpha channel, showing as a selection with the animated marching ants.

The Linear Tool

Now use the Linear tool. Keyboard shortcut 'v' (as in 'vector').

The linear tool will draw a line with whatever the current brush is. So, you can use it to make it a perfect line in the alpha channel.

Draw a line from upper-left to lower-right with the rubberband line.

When you release the mouse button to end the line, DOgwaffle draws the current brush along that path with whatever parameters are in effect.

You now have a nice linear selection.

Storing the Alpha Channel (the mask)

The Image (Buffer) menu has a well known feature called 'Store Buffer' (or Store Image). It's for temporarily storing and managing the current image's RGB channel. The Brush menu has a similar one, to store and manage the custom brush.

Likewise, there's a store option in the Alpha menu:

Alpha > Store apha...

The purpose of storing the alpha is to grab a snapshot of it.

You can then edit it further, modify it, replace it back into the active document work in progress etc...

For example, here's the snapshot, the store alpha channel image from the line we just drew a second ago into the alpha channel with the line tool.

The alpha brush we used as the crisp one, called "Hard 50".

If we wanted to blur the edges of the alpha selection mask we can use the filter in the alpha menu:

Blur alpha...

Select a large blur value and click OK

If you now use Store Alpha again, you'll notice that the edges are blurred.

You can either store a new instance from the Alpha menu. Or you can click the 'Get alpha' button to grab the current alpha into the previously stored interface.