[Scribus] Publishing question
Fri Sep 14 06:21:56 CEST 2007
> 8 bit colour depth won't affect your printing result at all, since
> hardly any
> print workflow I know of uses 16 bit.
More to the point, the "8 bit" being referred to here is 8 bit _per_
_channel_. For 3 channel images (RGB) that's 24 bits per pixel; for CMYK
it's 32 bits per pixel. Your computer display is at most 24 bits per
pixel. Though it might claim to be 32 bits per pixel, it's probably
really 24 bit, or just wasting every fourth byte for padding.
Of course, most computer screens can't display anywhere near that many
actual distinct colours; many of the 24 bit pixel values appear the same
on screen. Much of the rest of the bit depth is useful to permit colour
transforms without too much banding and loss.
In other words, when you're printing screen shots colour depth is not
even slightly significant as an issue.
What is a problem is resolution and compression.
As has been explained, your display will be somewhere from 90 - 140 dpi
(almost certainly 96-110 unless you use a really high detail laptop
display). You need to print at 300 dpi according to your printer. That
means that you must either scale the images up and suffer visible
blurring & pixelation, or you must print the screen shots at about one
third of the size they appear on the screen.
Taking a screenshot at higher resolutions, if you have a program that
does that, has absolutely no effect. The on-screen data is at screen
resolution, and all those programs are doing is scaling the image up for
you. If anything this will cost you quality rather than gain you
quality; scaling should usually be done once and only once, preferably
on output to PDF.
Compression is also an issue. Because you have so little detail to work
with and such a low resolution image, you must be very careful about
compression artifacts. This isn't helped by the fact that JPEG
compression is designed for photographic data and does not work well for
images with hard lines and large areas of exactly the same colour; it
tends to introduce highly visible artifacts. Avoid it at all costs for
You should if possible use TIFF images, simple bitmaps, or losslessly
compressed PNG images for your screenshots. These formats will avoid
introducing compression artifacts. Screenshots will be tiny files
anyway, and if you use TIFF you can use internal flate/zip or lzw
compression without introducing loss. PNG in maximum quality is also
lossless while still compressing quite effectively.
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