Optimizing Files For Processing And Printing; Resolution Of Raster Images - Xerox DocuColor DocuColor 4 User Manual

6.5
The following sections provide tips on how to create image files that pro-
duce the highest possible print quality while minimizing the processing time
and disk space they require.
6.5.1

Resolution of raster images

While a 72 ppi raster image appears sharp on a monitor, the same image
would likely appear pixelated when printed to the DocuColor 4 LP. Color
print devices are capable of much greater detail than monitors, and require
correspondingly higher resolution image files. However, high-resolution files
can be large, and therefore cumbersome to transmit over a network, process
for printing, store on disk, and edit.
Beyond a certain threshold, a higher image resolution greatly increases file
size while having a minimal effect on output quality. The optimal image reso-
lution depends on the resolution of the final print device. Aim for the resolu-
tion that optimizes both file size and output quality.
The resolution of a raster, along with its bit depth and physical dimensions,
determine its file size. The following table shows the file sizes of color raster
images at different dimensions and resolutions.
Image size
3" 4"
5" 7"
8.5" 11"
In this table, the shaded areas indicate that 200 ppi is typically the best trade-
off between image quality and file size. However, higher resolutions (e.g.,
250 to 300 ppi) may be needed for offset printing, when quality is of the
utmost importance, or for images containing sharp diagonal lines.
To find the best image resolution for your purposes, make test prints of some
raster artwork at different resolutions. Start with a high-resolution image (400
ppi) and save versions at progressively lower resolutions, down to 100 ppi,
using a pixel-editing application such as Photoshop. Always save a copy of
the original high-resolution version in case you need to revert to it. The high-
resolution data cannot be recreated from a lower resolution version.
Optimizing files for processing
and printing
100 ppi 150 ppi
RGB/CMYK RGB/CMYK
0.4/0.5 MB 0.8/1.0 MB
1.0/1.3 MB 2.3/3.0 MB
2.7/3.6 MB 6.0/8.0 MB
File size at:
200 ppi
RGB/CMYK
1.4/1.8 MB
4.0/5.3 MB
10.7/14.3 MB
6
400 ppi
RGB/CMYK
5.5/7.3 MB
16.0/21.4 MB
42.8/57.1 MB
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