Date   : Mon, 23 Jun 2008 15:50:35 +0100
From   : dllm@... (Dave Moore)
Subject: The Micro User

> Mike Tomlinson wrote:
> > In article <314mFTNIO6388S10.1213970833@...>, Dave
> > Moore <dllm@...> writes
> >> (I can't help but feel 600dpi is overkill for magazines, as you'd end up
> >> requiring terabytes and terabytes of space to store the lossless
versions).
> > 
> > The files should be highly compressible though?
> 
> Not in my experience - there tends to be a lot of noise in the data which 
> reduces the compression algorithm's efficiency. It is possible to skew the 
> greyscale range (i.e. fold several tones into one, just not linearly) in
order 
> to reduce filesize, but then it requires extra visual checks to make sure
that 
> important data's not being lost.

With reference to the greyscale pages featured here:
http://mags.acornpreservation.org/Micro_User/v3n1

Regarding my OFFLINE copies, I was able to reduce the grayscale images from
approx 8Mb per page (lossless 600dpi PNG) to 1Mb-2Mb per page (*still*
lossless 600dpi PNG) by simply increasing the contrast and 'blanking' the
plain/empty areas of each page i.e. removing the paper texture, so white areas
were pure white

But as Jules points out, you do need to carefully inspect every page to ensure
you aren't losing any detail (i.e. pale shades of gray).

-- 
Dave.