Date : Thu, 23 Apr 2009 00:17:55 +0100
From : jgh@... (Jonathan Graham Harston)
Subject: CoPro circuit diagrams
"chris whytehead" wrote:
> Here is a TIFF of the 32016 2nd processor circuit diagram
> http://acorn.chriswhy.co.uk/docs/Acorn/Manuals/32016CoPro.tif.
> Its about 4.3MB. uncompressed.
That's better resolution. Unfortunately, it is also fairly
unreadable, and I've remembered why. It's a two-colour image, so
there's no aliasing to make things more readable. Are you able to
scan it in 16-colour or 256-colour greyscale?
As a note for anybody interested, with the diagrams I've been
rescanning after a bit of experimenting I've come down to the
following method:
- I've scanned them at 600dpi 256-colour greyscale.
- I glue together any multiple sheets into single images, and
remove gross blemishes, such as spiral binding.
- I then reduce the colour to 16-colour greyscale.
- I flatten the first four colours to black and the last four to
white.
- I convert back to 256-colour greyscale to merge the pallette, and
for the next step
- I crop the image to an appropriate area in 1:1.41 ratio, ie
A-series paper aspect.
- I resample the image to 4096x2896 for A4 sheets or 5792x4096 for
A3 sheets
(Resampling changes the image size by sampling adjacent pixel
colours and antialiasing between them)
- I then reduce the palette back to 16 colours greyscale.
- I then flatten the first five and last five colours, leaving a
palette with just 8 entries, Squeezing a bit more compression
into a 3-bit pallette than with a 4-bit palette.
- Changing up to 256 colours and back down to 16 colours merges the
palette again.
- Do any final fine-detail blemish removal.
This seems to produce a fairly good combination of small file size
and detail retention. You end up with an implied resolution of
520dpi, so I could resample to something like 2500x3200 to get an
implied resolution of 300dpi.
--
J.G.Harston - jgh@... - mdfs.net/User/JGH
BBC IDE Hard Drive Interface - http://mdfs.net/Info/Comp/BBC/IDE