ART134 tut 1

ART134 tut 1, Grafika komputerowa, Tutoriale

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52
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December 2006
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TUTORIAL
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PHOTOSHOP
SCREEN-PRINT EFFECTS
Screen printing is a tricky, messy process, but it’s the less than perfect areas that create that distinctive look.
Here, Computer Arts regular
Derek Lea
reveals how to simulate silk-screened imperfections in Photoshop
ON THE CD
Screen printing is a process suited for
printing on unconventional surfaces,
such as clothing or outdoor signs. You
won’t ﬁ nd much screen printing done on
paper, unless of course you look at the work
of Andy Warhol or the poster art of Frank
Kozik. Generally, paper is the domain of
the four-colour process, or CMYK printing,
which creates very precise results. Screen
printing is far more rough and ready.
When a design is colour separated for
screen printing, a ﬁ lm positive (rather than
a ﬁ lm negative as is used in photography)
is created for each colour. Areas of 100 per
cent black will reproduce as 100 per cent of
that colour, and coarse halftone screens are
used to create percentages of those colours.
Each positive is used to create a separate
screen, which ink will be forced through
with a squeegee on to the desired surface.
Usually all screens are crudely registered
on a carousel-like device and ink is applied
to the surface, one colour at a time.
In this tutorial you’ll use Alpha Channels
in Photoshop as your screens – scanning
a hand-drawn positive and placing it into
each new channel. A selection will be
generated and then ﬁ lled with colour on a
new layer. To make your channels behave,
you’ll need to alter the default settings in
Photoshop ﬁ rst. So, as you get to the point
where you create your ﬁ rst Alpha Channel,
double-click it in the Channels palette.
When the Channel Options appear, change
the Colour Indication setting so that colour
indicates selected areas rather than masked
areas. By doing this, you’ll be able to
generate selections without having to invert
them each time.
You’ll ﬁ nd all the ﬁ les
you need to complete
this tutorial in the folder
marked Tutorial\
Screenprint on this
issue’s CD.
TIME NEEDED
40 minutes
INFO
Derek Lea
is an award-
winning
illustrator,
published
author and part-time
instructor at both
Centennial College
and the International
Academy of Design in
Toronto, Canada. You can
check out his upcoming
book by visiting www.
focalpress.com, or see
more of his work at
www.dereklea.com.
1
First, dust off your felt-tip pens and
2,000x2,000 pixels at 300dpi, with
a purple canvas colour. Drag the wave1.jpg
ﬁ le from the CD into your new ﬁ le. Re-size
it using Edit>FreeTransform. Select the
Magic Wand, ensure Contiguous is enabled
and select the wave’s white caps.
start drawing the outline art for each
element. Then, place a sheet of tracing
paper over your drawing and cover areas of
the tracing paper that require shading with
black. This will create a mechanical ‘positive’
for the shading colour.
and ﬁ ll the selection
with light blue. Deselect
and use the same method to select the other
areas of the wave. Now create a new layer
and ﬁ ll the selection with red. Change the
Layer Blending Mode to Multiply. Disable the
visibility of the black-and-white Wave Art
layer. Open the wave2.jpg ﬁ le from the CD
and Copy the image.
2
Use this method to create a ‘positive’
for each different shading or highlight
colour. When you have created a stack of
different pages, or ‘positives’, for each
individual character or image element, scan
all of them separately and save them as
individual ﬁ les. Alternatively, use the scans
supplied on this issue’s CD.
Tutorial and illustration by Derek Lea
www.dereklea.com
April 2007
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In Photoshop, create a new CMYK ﬁ le,
4
Create a new layer
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TUTORIAL
PHOTOSHOP
the copied image into the channel. Select Filter>
Pixelate>ColourHalftone from the menu, set the
maximum radius to 15 pixels and set all of the screen
angles to 45 degrees. Click OK to convert your black-and-
white art to a dot pattern.
8
Now Paste the copied art into a new channel
within your working ﬁ le. Load the channel as
a selection, then create a new layer. Fill the active
selection with blue on the new layer. Deselect and
set the Layer Blending Mode to Overlay. Position
and rotate the new layer using Free Transform.
organised. Next, open up the squid1.jpg ﬁ le
from the CD and Paste it into a new channel within
the working ﬁ le. Load the channel as a selection and
then ﬁ ll it with purple on a new layer. Invert the
selection and create a new layer. Drag the new layer
below the top layer in the Layers palette.
6
Next, load the channel as a selection and create a new
As before, Paste this image into your working
ﬁ le and use it as your guide to repeat the process of
adding layers of ﬂ at colour, deﬁ ned by Magic Wand-
based selections. Reduce the Opacity of the White
Cap layer so you can see the other wave beneath it.
Wand and ensure that
the Sample All Layers option is disabled. With your
new layer targeted, Alt/Option-click on areas
surrounding the squid to deselect them. Fill the
selection with yellow on the new layer and deselect.
Now use the Move tool to offset the layer from the
outline layer above it.
layer. Fill the active selection on the new layer with
purple, sampled from the background. Deselect and use
Free Transform to position the layer contents over the
appropriate area. Open up the wave3.jpg ﬁ le and choose
Image>Mode>Bitmap from the menu.
CHANNEL PREVIEWS
When you’re pasting
artwork into an Alpha
Channel, you can position
it within the channel with
the aid of the Composite
Channel. With your
current Alpha Channel
targeted, simply click in
the column to the left of
the RGB Composite
Channel in the Channels
palette to enable its
visibility. You’ll see your
channel appear as a red
overlay against the
image. This is helpful
when positioning your
channel’s artwork before
you load it as a selection.
300dpi and set Method to
Halftone Screen. Click OK,
then set Frequency to 15 lines
per inch, Angle to 45 degrees,
and set Shape Option to Line.
When you’ve converted the
grey to a line pattern, Select
All and Copy.
and Paste both wave4.jpg and wave6.jpg into
Alpha Channels of their own. Use the Colour Halftone
ﬁ lter to convert each channel to dot patterns. Fill
the channel-based selections on two new layers.
Rotate and position the artwork as necessary.
open the squid2.jpg ﬁ le from the CD. Copy
this ﬁ le and Paste it into a new Alpha Channel in
your working ﬁ le. Convert it to a halftone dot pattern
and then load it as a selection. Fill the contents with
green on a new layer. Deselect and reduce the Layer
Opacity slightly.
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Create a new channel in your working ﬁ le and Paste
11
Group all of your wave layers to keep things
12
Select the Magic
9
Next, open up the wave4.jpg ﬁ le from the CD.
7
Leave Resolution set to
13
Reduce the opacity of your layer and then
10
Repeat the methods used previously to Copy
TUTORIAL
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and then
open up the
squid4.jpg ﬁ le
from the CD.
Convert this ﬁ le
to a bitmap and,
again, use the
halftone method
with the same
settings as before to convert it to a 45-degree
line pattern. Copy the image and Paste it into
the working ﬁ le as a new channel. Load the
channel as a selection.
HALFTONE AND
GREY VALUES
When you use the Colour
Halftone ﬁ lter in a
channel, or convert a
greyscale ﬁ le to a bitmap
using the halftone
conversion method, bear
in mind that the density
of the pattern you create
is directly related to the
density of the blacks
within your image.
A lighter grey colour will
produce thinner lines
with wider spaces or
smaller dots with lots
of negative space in-
between them. A darker
grey, on the other hand,
will produce thicker,
closely packed lines and
dots that are touching
each other.
14
Open up the squid3.jpg ﬁ le and
This has all the individual greyscale
ﬁ les required to create the screen-printing
effect within it on a series of layers. Use the
methods you’ve used so far to add another
creature to the left. Group the layers that
make up this creature when you’re ﬁ nished.
convert it to a bitmap. Use the same
45-degree angle line pattern that you used
for your previous conversion. Copy and
Paste it into a new channel in your working
ﬁ le. Again, load the channel as a selection
and ﬁ ll it with colour on a new layer.
target the
layer that contains
the squid outlines.
Use the Magic Wand
to select the eye
areas from this
layer and create
a new layer below
the top layer. Fill the
active selection with
the current foreground colour. Deselect,
change the Blending Mode to Screen,
reduce the Layer Opacity and offset the
registration slightly using the Move tool.
ADD/SUBTRACT
WITH A WAND
palette and ﬁ ll the active selection with
the same colour that you used for your squid
outline, many layers ago. Deactivate the
selection and then group all of the squid
layers together, which will help to keep the
Layers palette organised.
the CD. Again, all of the separate
components you need to create your
channels are there. Copy and Paste the
individual layers into your working ﬁ le as
channels. Use the same methods again to
create another creature in a group at the
right. Offset each layer generously this time.
When you target an area
of an image with the
Magic Wand you can add
additional areas to the
active selection by Shift-
clicking on them. If you
accidentally add an area
to your selection that you
do not wish to include,
Alt/Option-click on that
area to remove it from
the selection.
process one last
time to add another
creature as a group of
layers to the working
ﬁ le. Access all of the
components for this
creature within the
small3.psd ﬁ le. At this
point, feel free to tweak
individual layers, add
extra halftone effects,
and make any other
colour adjustments you
fancy to embellish
things further.
use the Elliptical Marquee tool to
draw a series of elliptical selections under
or near the squid’s iris area and spots. Fill
the active selection on the new layer with
pink. Deselect and then draw an elliptical
selection on the iris. Delete the colour from
this selected area.
it needs a little reﬁ nement in terms of
colour. Yours will differ slightly, but feel free to
enhance the overall colour using Adjustment
Layers. Here, we’ve used a combination of
levels and selective colour adjustments to
snap up the colour and contrast.
April 2007
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Deselect
20
Open the small1.psd ﬁ le on the CD.
15
Deselect and
18
Create a new layer in the Layers
21
Now open up the small2.psd ﬁ le from
22
Repeat this
16
Create another new layer. This time,
19
Take a look at the image as a whole –
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