LXF122.tut_gimp.pdf

Tutorial Gimp

Gimp Open source image-editing

software you can get your teeth into

Gimp: Going to warp speed

Want to explore strange new worlds and seek out new inspirations in your art?

Michael J Hammel shows you how to make the jump using Gimp.

my creative side, it’s time for a tutorial that is a bit

more repeatable and not quite so complex. If you’ve

spent your time this summer anywhere except hiding behind

Saturn’s moon, you’ll know that a stellar rebirth brought a

rejuvenated Star Trek back to the cinema. In homage to this

re-envisioning, this month I’ll show you how to add a warp

speed effect to your projects.

What we’re looking for in this project is an outcome similar

to the warp speed effect in the original Star Trek: The Motion

Picture movie from so many years ago. For those of you who

haven’t dusted off your trekkie memory banks in a while, let’s

recap: the USS Enterprise engages warp speed and pulls an

asteroid in with it, turning the warp field into a wormhole.

Everyone goes motion-blurry for a few minutes until they

destroy the rock. Then Kirk goes all superior on his number

two for making him look bad. Here, we’re going to follow our

shipmates into warp space and leave the wormhole stuff for

the navigator to figure out.

For the cadets

Although there are a lot of steps to follow for this tutorial,

none are particularly complex or require anything other than

the stock features found in the latest version of Gimp (2.6).

We’ll only be creating a few layers too, which means this

project won’t be too taxing on slower systems or small

displays. Most importantly of all, this is a do-it-yourself

project, so there are no stock images to track down this time.

I’ll also be going into a little more detail than I have in previous

months in order to help you if you’re new to these articles and

still leaning toward the beginner level.

Prepare to engage

Open a new image window with a white background set to

1250x1250 pixels. Note that this tutorial will work better with

a square image window, because of the rotations we’ll be

performing near the end of the process. Now the size of the

image might be a bit large for your project, or it could be a bit

too taxing for your computer to handle. If that’s the case, just

halve all the pixel counts. The end results should be

essentially the same at half the size.

Choose Rectangle Select from the toolbox and draw a

rectangular selection anywhere in the image window. The size

and position of this initial selection don’t matter, because

we’re about to change it manually. In the Tool Options dialog,

set the Size to 1250x40 pixels and the Position to 0x605. This

will create a selection 40 pixels tall that spans the width of the

image window and is centred on our canvas.

Complete the selection by hitting Enter. Copy (Ctrl+C) and

paste (Ctrl+V) the selection to a new layer. Name this new

layer Noise. Open the Hurl filter (Filters > Noise > Hurl) and

set the Random Seed to 10, the Randomisation to 1% and

Our

expert

Michael J

Hammel

is a contributor to

the Gimp project

and the author of

three books on the

subject, including

his latest, The

Artist’s Guide to

Gimp Effects.

If a Scotsman complains that the Gimp “cannae take any

more Cap’n,” don’t believe him.

Last month We turned up the heat and created a beautiful fire goddess.

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A fter two months of you being patient while I indulged

Gimp Tutorial

Gimp: Going to warp speed

immediate update to the other field. However, as only the

Height needs to be scaled here, you should click on the link

icon to the right of these two fields so that the link appears to

be broken. This will let you change the Height and Width of

the object you’re scaling independently of each other.

Since the layer we’re working with was initially centralised,

the scaling should keep the Noise layer directly aligned with

the background. If it doesn’t, use the Align tool. This tool

requires you to click on each layer, one at a time, in the image

window to align them. So, aligning the Noise layer with the

background means clicking on the Background layer first,

followed by the Noise layer and then using the Relative To

option. Since this process shouldn’t be necessary, I’ll leave it

as an exercise for the curious reader.

With the Noise layer active in the Layers dialog, merge

(Layers > Merge Down) the Noise layer with the background

layer. Doing this will give the merged layer the same name as

the bottom of the

two layers that

were merged, so

Background in this

particular case.

Now it’s time to

invert the colours

(Colours > Invert). Suddenly, the project begins to take shape,

but the streaks need to flow from the outer edges of the

image window towards the centre. The first step is to map the

image into polar coordinates.

Open the Polar Coordinates filter (Filters > Distorts > Polar

Coordinates). Set the Circle Depth to 0 and the Offset Angle

to 0. If the former isn’t set to 0, the distortion won’t map to

the full size of the square image window. Technically, the latter

could be set to anything, but I’ve chosen to use 0 to make it

easier to remember this process. There are three options at

Quick

tip

The number of

streaks all depends

on the amount of

noise in your Noise

layer. Increase the

noise if you want

more streaks.

“Rescaling will stretch

the dots from the noise

into vertical streaks.”

It looks like we’re not making use of all our canvas space,

but don’t worry – soon this will be a streaking warp field.

Repeat to 2. Click OK to apply the settings to the Noise layer.

Note that the Random Seed and Repeat values can be

changed as you desire and increasing the noise will produce

more warp streaks. However, too much noise will clutter the

final product with streaks, so don’t overdo it.

You’ll probably notice that the Hurl filter has essentially

thrown dots of colour on the current layer within the

selection. This project doesn’t need the colour, though, just

the dots. Desaturate (Colours > Desaturate) the Noise layer

using the Luminosity setting. Luminosity brings out the dots

better than the Lightness and Average settings, but feel free

to choose a different Desaturation option if you prefer.

The contrast between the space and the dots can be

improved further using the Levels dialog. Set both the Black

Point and White Point, represented by eyedroppers between

the Input Levels and Output Levels graphs, to 180. Click OK to

apply this change.

When dots go streaking

At the moment the colours are inverted for the warp speed

effect (the dots are black and the background is white), but

this will be addressed momentarily. Before that, the Noise

layer needs to be rescaled to fit the image window. Rescaling

will stretch the dots from the noise into vertical streaks.

Scale the Noise layer (Layer > Scale Layer) to 1250x1250

pixels. The Scale dialog keeps the aspect ratio by default,

which means changes to either Height or Width cause an

This close up shows the Levels adjustment has darkened

the noise (before is upper left and after on the lower right),

which will improve the visibility of our warp streaks later.

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Tutorial Gimp

The Scale dialog defaults to changing Height and Width

proportionally, but clicking the link icon will alter that.

Curves provide a useful way of enhancing the contrast of

our warp streaks for a more potent effect.

Quick

tip

the bottom of this dialog: Map Backwards, Map From Top and

To Polar. Only the To Polar option needs to be set. The other

two aren’t necessary for this example, but setting them

shouldn’t adversely affect the final results.

The streaks in the image might be too bright or too dim at

this point, depending on the work you did with the Noise layer

earlier. If they’re too dim, duplicate the Background layer and

set the duplicate layer’s Layer Mode to Screen. If there are

too many streaks, set the Layer Mode to Overlay instead.

Once that’s done, you should merge the two layers.

Stretching the field

The image should now look like a bad approximation of the

warp speed effect. Fortunately, Gimp gives us the tools to

make it better. Applying the Polar Coordinates filter stretches

the streaks slightly, but they need to be lengthened even

further. This is done using the Motion Blur filter, so open it up

with Filters > Blur > Motion Blur. Be aware that the preview

window may be slow to update depending on your system’s

resources, so you may need to be patient. Set the Blur Type

to Zoom and centre the effect at X = 625 and Y = 625, making

sure that the Blur Outward option isn’t set. The Length

parameter should be somewhere around 50 to 100 – note

that larger values will stretch the streaks more, but might dim

them too much. In this example, the length was set to 100.

There are several steps that can be performed at this

point to improve the streaks. If the streaks are too dim,

duplicate the layer and set its Layer Mode to Screen, then

merge the two layers. If this causes too many new streaks to

appear, these can be addressed by using the Curves or Levels

dialogs. Here, I used the Curves dialog to adjust the Value

curve (as shown in the screenshot above), brightening nearby

streaks and removing dimmer streaks from view.

Colouring the field

Before we get on to the final few steps, it’s time to add colour

to the plain white streaks to make them more reminiscent of

Star Trek: The Motion Picture’s effect. Before starting, ensure

you have just one layer, which should be the Background

layer. If there are more layers than that, merge them until only

the background remains. Duplicate the Background layer.

Open the Colourize dialog (Colours > Colourize) and set the

Hue to 220, Saturation to 90 and Lightness to -40, then apply

these settings to the layer. Name the layer Blue, because

these values will colour the streaks blue. Now set the Layer

Mode to Screen and rotate the layer 90 degrees clockwise

(Layer > Transform > Rotate 90 Clockwise).

With the blue tint added, it’s time to add some red streaks

to our effect. To do this, select the Background layer in the

Layers dialog again. Open the Colourize dialog as you did

before, but this time set the Hue to 360, the Saturation to 60

and the Value to -40. This will tint the layer red. It’s worth

noting that setting the Blue layer’s Mode to Screen is what

allows the red streaks to show. In an image such as this –

made up of black and one other colour – the Screen mode

acts similarly to the Addition mode, where the pixels in the

There’s not much

colour in this image

compared with the

black background.

This makes using

most layer modes

impractical, since

many will subtract

the streaks right

out of the picture.

Applying the Polar Coordinates filter to the inverted

streaks creates the foundation of the warp speed effect.

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Gimp Tutorial

Rotating the upper layer offsets the streaks, and setting

the layer to Screen allows the red coloured streaks on the

lower layer to show through.

Screen mode layer are added to the pixels in the layer below.

Black pixels in the Screen mode layer won’t change the

appearance of the pixels in the layer below, however.

A few adjustments

We’re close to our final product, but the intensity of the

streaks can be improved. Select the Background layer and

open the Levels dialog. Set the Black Point field to 25 and the

White Point to 170. Now select the Blue layer and open the

Layers dialog again. This time set the White Point to 170,

leaving the Black Point at 0.

Creating a central star

The image is essentially done at this point, but there’s one

more thing we can do to spice things up a bit. It’s time to add

a central star at the focal

point of the warp field.

There are many ways

we could achieve this

effect. For example, we

could use the Paintbrush in

tandem with a soft-edged

brush, scaled appropriately. The Super Nova filter could be

used or, to get really fancy, we could employ the Sphere

Designer filter’s skills. However, the method I’ve chosen for

this project is the Gradient Flare filter.

Start with a new transparent layer. Name this layer

Gradient Flare. Now fire up the filter via Filters > Light and

Shadow > Gradient Flare and click on the Distant_Sun entry

in the Selector tab. At the bottom of the dialog, click on the

Copy button and name the copy Warp Speed. With the new

entry highlighted, click on the Edit button to open the

Gradient Flare editor.

In the General tab, set the Glow Paint mode to Normal and

the Opacity to 100, Rays Paint mode to Normal and Opacity

to 90, and the Second Flares to Normal with the Opacity set

to 0. This gradient flare won’t use the Second Flares. Now

select the Glow tab, set the Radial Gradient to %white_grd,

the Angular Gradient to %white and Angular Size Gradient to

%white. Under the parameters

set the Size to 10%, the Rotation

can be left at 0 and the Hue

Rotation left at 55.0.

In the Rays tab set Radial

Gradient to %white_grd, Angular

Gradient to %Flare Glow Angular

1 and the Angular Size Gradient to %random. Under the

Parameters you need to set the Size Percent to 104, Rotation

to 140, Hue Rotation to -12, Number Of Spikes to 63 and

Spike Thickness to 90.

Finally, click OK to accept the changes to the Warp Speed

flare, and then click OK again in the Gradient Flare dialog to

apply the flare to the transparent layer we created earlier. The

flare can be coloured using the Colourize dialog. Here, I tinted

the flare with yellow.

Finishing touches

The last step in our process is optional – so try it out and see

if you think it improves your work. When I reached the end of

this tutorial, I found that there was quite a bit of pixellation in

the streaks when I viewed the image at full size (I typically

work on these projects while zoomed out a bit). To

compensate, I applied a Gaussian Blur of three pixels to each

layer. This lightens the image slightly, so further adjustments

using the Levels or Curves dialog may be required. LXF

Editing the

Gradient Flare

dialog will

produce the

distant star in

the warp.

Quick

tip

“Black pixels in Screen

mode won’t alter the

look of the layer below.”

A distant star field

behind the warp

field is another

optional step.

Create a noise layer,

desaturate it and

place it on the top

of the layer stack.

To hide the stars

behind the streaks,

add a layer mask

and copy all the

streak layers to it.

After some adjustments you should see brighter streaks

near the edges, tending toward blue, that fade away.

Next month Scan everyday objects as an alternative to stock image sites.

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