Re: Which Image quality should I use ?

["Joshua Krämer" <joshua.kraemer-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 2014-07-12, 14:58, Pol Stra wrote:

> I wonder, what can I do to reduce the size of those files while
> keeping a printable quality document?

Besides reducing the resolution, you can reduce the number of colours
used in a PNG picture, which is called colour quantization.  For
example, we can differentiate between ca. 12 levels of gray (between
black and white) with our eyes.  So it is useless to differentiate
between hundreds of different colours in a gray picture.  I quantize
all my gray pictures to use 12 colours only, and the difference is
usually not visible, but it leads to a much smaller file size.  For
coloured pictures, you need of course more different colours, you have
to try different values with each picture to find the best number.  I
use the tool pngnq for quantization.

After quantization, one can further losslessy compress an image by
removing unnecessary meta informations from the file, which can be
done automatically with the tool Trimage.

I've got both pngnq and Trimage from the repositories of my Linux
distribution.

Kind regards,
Joshua


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