Print Workshop - Part 1

Digital preparation of positives for screen print. 

Analogue techniques for preparing positives: true grain / stencils. 

Commercial print process - magazines, 1000s of copies.

Photoshop, illustrator and InDesign were developed for the commercial print industry so they are set up to deal with commercial printing processes. 

Image colour modes:

RGB (red/green/blue) - computer screen display, colour using light.

CMYK (cyan/magenta/yellow/key(black)) - how colour is defined for printed image, this is how full colour printed images are built up. 

Spot ink - the actual colour of what you want to print. 

It is cheaper to use spot inks as fewer inks are used in total. 

It is used when colour accuracy is essential, in branding and logos for example. 

It is used for colours which cannot be produced using CMYK such as fluorescent or metallic inks. 

Colour separation - when you separate an image in a way where you end up with a positive for each ink being used. 

Method 1

Magic wand tool -> select and area of a certain colour.

Select -> Similar

  

This selects all of the areas of that specific colour, this can then be copied onto a new layer so that it is by itself. 

Method 2

Select -> Colour Range

Click on the image to show the colour selection.

Use the 'Fuzziness' bar to increase or decrease the amount of pixels that are being selected. 

Selection Preview -> White Matte

This allows you to view your selection on your actual image, you can zoom in as normal. 

Click okay when you are happy with the selection.

Either copy and paste it onto a new later using Cmd+C and Cmd+V. 

OR use Cmd+J to copy the selection directly onto a new layer. 

Repeat the process for each colour. 

Make sure to label the layers with the colour they are supposed to be printed in. 

Positives need to be solid black. 

Select one of the layers prepared as explained previously. It should only contain transparent pixels and colour pixels. 

Select the layer you want to work with and click the checkerboard tile next to 'Lock'. 

This locks the transparent pixels so none of these can be changed. 

Edit -> Fill -> Contents -> Black

Coloured pixels will change to solid black. 

Repeat this process for all colours including any black layers. 

Even if it looks black it may not be pure and a positive needs to be 100% black so its best to change it anyway just to make sure. 

NOTE: Make sure to check image size - best to do this before you begin separating colours so all of your separate layers will be the correct size. 

How to separate colour for CMYK printing. 

This can be used in screen print to make a full colour image. 

Preparing this image for print using spot inks would be almost impossible because there are so many different hues. 

Two processes for separating it…

1. A3 size or smaller, positives would be printed on laser printer.

2. Larger than A3 - positives would be printed in digital print resource. 

The printers work differently. 

Method 1

Check image size. 

Make sure colour mode is CMYK. 

Save the image as a tiff or psd file. NOT JPEG. 

Channels - store information about colour. 

Click on thumbnail of one channel to view it in isolation (it will appear in black and white). 

Darker areas show that more of that colour is present. 

Make other channels visible to view the combinations (in colour). 

Each colour channel would work as a positive for silk screen.

  

Cyan and yellow

Magenta and yellow

Cyan and black

Create a new page in illustrator. 

File -> Place -> Select file to work with 

The image must be PLACED into illustrator, not OPENED. 

File -> Print (use black and white printer)

Output -> Mode -> Separations (host based)

Document ink options become available. 

Process colour = CMYK. 

If I printed now I would get four greyscale positives. 

How to print the variations of tone in a way that can still be used as a positive for screen printing (needs to be pure black and pure white).

Halftone Screen - enables us to print a variation of tints of that particular ink. 

Grid of dots equally spaced but varying in size to create different tints. 

Halftone dots are printed at different angles so that they don't end up printed directly on top of each other. 

Frequency - number of dots (lines per inch)

Frequency for commercial printing is around 150 - 200lpi. For screen print, 50 - 65lpi is more appropriate as it is a harsher process. 

The lower the number, the more the dots will be visible -  you could work towards this aesthetic by experimenting with this. 

Angle - angle which that set of dots will be rotated by. 

Angle values to remember

Using illustrator to separate colour means you only have to press print once and it doesn't affect your actual image. 

Method 2

For images larger than A3. 

Everything is done in Photoshop. 

Channels palette menu -> split channels. 

Each channel comes up as a separate greyscale image in different tabs named by colour. 

Smaller format printers can handle halftones but larger ones can't so you have to create them on the actual image yourself. 

Image -> Mode -> Bitmap (only works with greyscale images)

Pixels become either black or white. 

To preserve detail work with a higher resolution (1200).

 Halftone screen options -> input same values an in illustrator and choose the shape you what the halftones to be. 

Do this to all split channels. 

Input the same frequency to all but make sure the angles follow the 15, 75, 105, 155 degrees pattern. 

Example of one bitmap layer. 

Printing created dots on a laser printer can cause interference as it uses its own dots system too. 

Make sure you use the correct printer for your process. 

Laser printer - A3 or smaller, use Illustrator or InDesign. 

Largescale printers - bigger than A3, halftones created on Photoshop.