XJ128 and XJ128 Plus Printhead
XJ128 Guide to Operation
Xaar Document no: D031010302 Version A
Page 49
9.1.2 Image processing software
There are many pieces of software available to manipulate image files in preparation for printing. The
most popular low cost solution is probably Adobe Photoshop
available on Windows and Macintosh.
Examples from Adobe Photoshop
version 5.5 will be given for each stage of the image processing
procedure. More expensive commercially available RIP
’
s and custom
-drivers are likely to be required
for some printing applications using Xaar printheads.
9.1.3 Colour spaces
Digital images are displayed in a variety of colour spaces. RGB (images made from primary colours
red, green and blue) is a common format for scanned digital images, as the range of colours possible
is large
The required format for printing with Xaar printheads is CMYK (images made from the primary
colours cyan, magenta, yellow and black). This often means the colour space of an original scanned
digital image has to be changed from RGB to CMYK although images are also scanned in CMYK
and digital cameras can record images directly in to a CMYK format.
RGB and CMYK colour spaces are device specific. For example a scanner will have a certain range
of colours it can record and similarly printing inks only have a certain range of colours they can
produce.
The range of colours perceived by the human
eye is much higher and many methods of
trying to record colour as a value have been
tried. Today the most common way to describe
colour is the CIE LAB colour space.
Commission Internaitionale de L
’
Eclairage
(CIE) developed a colour measuring system
based on the way the human eye perceives
colour. They developed a standardised version
called CIELAB. This is the most widely
accepted concept for the subjective description
of colour.
Photoshop
uses a Lab colour look up table
when converting between colour spaces to try
and get as close to matching colours as possible.
Figure 9.1 - Device colour spaces vs. CIE Lab
1
The aim of colour processing as to maintain the colour information of an original image in a printed
output as accurately as possible or is needed for a particular application.
1
Image courtesy of Gretag Macbeth