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the Color Gradient

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What is a Color Gradient?

It's a change in color, and in opacity (or it's opposite, transparency).  It is used by a number of tools.

In PD Particles, the color gradient is used by the particle brushes. The colors showing from left to right are the colors that the particles will go through.

In this example, using PD Artist, a slightly more sophisticated color gradient is used with the Fill tool, in this case with a vertical layout. This can be used to create hazy skies with sunset colors.
Another tool that can use the color gradient is the linear gradient tool. In this case we used zero opacity on both ends of the gradient, so that either end remains transparent.

And here's yet another tool that can use the color gradient: the circular gradient tool. The left-most color from the gradient is used in the middle of the circle, and then it progresses to the right-most color as it draws towards the end of the circle.

The opacity channel has several high and low points, alternating from opaque to transparent, to let you see through the corresponding rings.

These are examples of color gradients at work in other programs. Now let's take a look at how to use the color gradient with PD Particles, and how to set and define it in the first place.

We'll use particle brushes, and the color gradientwill be used to control the changes in colors during the particle's lifespan. The left-most color in the gradient will be the starting color of the particle trace. Here we see an example using the Style 'Shrinking line'. By the end of the particle (near the bottom, thin tip), they have reached the right-most color of the gradient.

You can open the color gradient panel from the Window menu.

There is also a keyboard shortcut, 'p' for p)laytime..... or was it P)icasso-colors?

And you can also find the current gradient's color strip in the Particles panel. If you click that gradient color strip, it too will open the gradient panel.
The default particle brush might be a bit thin and it might be difficult to recognize the essence of the color gradient, so we'll use a different setting. We'll use in fact an internal brush, such as a large airbrush, and then we'll select that for use along the particle traces.

Select the Large airbrsh.

Next, change the Style in the Particles panel from Line to 'Brush' style. In this mode, it will use the currently selected brush instead of the default fine lines.

This will make it easier to see how the color gradient applies along the particle traces.
Make sure that the particles are enabled. It would have been  disabled when selecting that airbrush a few steps earlier.
Also, let's disable the 'Shading' option. Otherwise, the color will be darkened for particles which grow downwards.
Now let's draw a few dabs of particle traces. You can see very well now how the particles change their color from red through yellow-green to light blue-cyan, just like the selected color gradient.

Let's take a look at the options in the color gradient.
There is a button to reserve the gradient. It flips it 'horizontally, left-to-right.

Now the particles start with cyan and end with red.

There are multiple gradients selectable.

Note that selecting it in the gradient panel doesn't make that the current gradient for the particles though. You have to select the desired gradient index from the Particle panel's slider.

Here we have selected a different gradient index in the Particle's panel. The slider is right below the color gradient strip.

The gradient index is one of 8 indices available from the c`urrent gradient collection.

There are additional gradient collections available.

Click the 'Gradient' button, and you will see other sets.
Click the desired gradient set.
Here's a new gradient, freshly loaded.

Note that the opacity is changing up and down several times.

Changing Colors

It is possible to directly change the progression of the opacity as well as the progression of the color channels.

Simply place the pointer into the gradient color area.  Start dragging left to right, and up and down.

Select the Red tab if you want to change the red channel's progression.

Likewise, select the other channels as needed.

The resulting color will be shown.
When you change the progression a bit too abruptly, you may want to smooth it.

There are two buttons that smooth the gradient. One is a one-time smoothing. The other is a toggle that turns smoothing on and keeps smoothing until you click it again to turn it off.

Drag-and-Drop Color

Another way to change or set the colors is by drag-and-drop from the color well.

Simply click a color square and drag it over to the gradient. Drop it on the scale near the bottom of the color gradient.
In this way you can create new gradients that are set by specific colors you want, sort of like a keyframe or key color. You can create such colors with the colorpicker or by numerically setting the R, G and B values, and dragging the color from the primary or secondary color rectangles into the color well. Then you can drop it to the gradient's scale.

You can also drag-and-drop directly from the primary and secondary color rectangles to the gradient scale.

When you want to get rid of a key color along the gradient scale, just click and drag it out of the gradient to the left or right to dismiss it.

Here's another trick. Using just a change of opacity, you can make grass that thins towards the end. Or, to the contrary, make it suddenly turn opaque again. If the color also turns from dark to bright around where the opacity spikes, then that can convey an illusion of flowery tips at the end of the grass helms.

In this example, the gradient starts with dark brown for the wooden stem, with full opacity. It then turns green and quickly drops to semi-transparent to make it look like thin pine needles. In the end it brightens to a yellow with full opacity again, to make it look a bit like fern blooms. Notice also how the length of the needles varies a lot with the speed of the brush stroke.

That's about it. The color gradient is not a very complex tool in PD Particles, but it is nonetheless very powerful and can lead to great many new results with new types of particles, especially when used with other attributes such as shrinking lines, splits, opacity changes, tinting and fog etc...