XJ128 and XJ128 Plus Printhead
XJ128 Guide to Operation
Xaar Document no: D031010302 Version A
Page 48
9 Image Processing
9.1 Image processing background
Image processing is a very important part of a printing application depending on the quality of results
desired and the limitations of the system being used.
For example, in a very simple application such as printing a monochrome barcode on to a box with a
200dpi binary printhead, the scope and need to do any image processing is small. However, even
such a simple application could require the amount of ink being put down on to a substrate to be
controlled by image processing.
Some applications such as wide or grand formatting graphics printing require emphasis on high
quality image processing RIP
’
s and advanced interleaving techniques to achieve optimum printing
results.
For a high-end application such as printing photographic quality images on to an identification card
using a greyscale-technology printhead, the amount of time and effort put in to the image processing
would be greatly increased. The colours would have to be reproduced accurately from a digital
original controlling ink levels and characteristics to a fine degree.
A separate image process will be required for each different combination of the printing ink, substrate
and printhead used in a particular system.
Whatever level of image processing control is required for an application there are
some fundamental steps that need to be followed regardless of the application:
1. Image must be the correct size for a particular application and printhead resolution.
2. Image data must be in a
‘
CMYK
’
or
‘
greyscale
’
format for further processing.
3. The amount of ink going on to a substrate may need to be controlled.
4. Image data must be split into individual colours for each individual printing head.
5. A pattern may need to be applied or image may need to be split in to discrete levels if
greyscale is being used.
6. An image is required for each printing head in the correct file format.
9.1.1 File formats
Digital images come in a variety of file formats. Some common ones are tiff (with file extension .tif),
bitmap (.bmp), jpeg (.jpg), Photoshop
(.psd). Bitmap files are required to print with a Xaar evaluation
kit. A binary image is saved as a 1-bit bitmap whilst a greyscale bitmap is saved as a 4-bit bitmap.
Tiff files are a high quality, high memory image type. Jpeg files can be used to compress image data.
Photoshop
image files can contain supplementary information such as layers in an image.
Pixel values in a digital image will range from 0-255. The quality of an image cannot be improved by
image processing. It will depend on how the image was originally captured.
