Re: VMs: RE: Map scans now posted...

[Nick Pelling <incoming@xxxxxxxxxxxxxxxxx>]

Hi everyone,

> > There is no visible advantage to 400 dpi, at least not on Windows systems
> > and in Paint Shop Pro,
>
> Independently of what the image is?

The point about the TIFFs I scanned in was that they should be at a higher 
resolution than normal screen resolution, so that anyone can zoom right in 
to examine the extraordinarily fine detail in them. I've spent a fair bit 
of time with a magnifying glass looking at the image in Kraus, but the 
half-tone often interferes with the detailing - if the half-tone can be 
removed, then I can try out super-resolution techniques to try to predict 
higher-order detail (otherwise it'll just be GIGO). :-o

> > but the difference in file size between 300 and 400 dpi is tremendous.
>
> How tremendous? You mean there is a sudden unexpected size increase
> between those particular resolutions, compared to other resolution
> changes? That could suggest some software problem...

dpi is one-dimensional, but scan size is two-dimensional, so the difference 
between 300dpi and 400 dpi is 3x3:4x4, ie 9:16 (ie, nearly 2x the size) - 
so a 600dpi scan would be 3x3:6x6 = 9:36 = 4x bigger.

Also: if you start getting down to the grain of the image, you start having 
to encode the surface's texture noise, which can worsen the compression 
performance etc.

> > TIFF uncompressed scans at 600 dpi would be huge,
>
> If a lossless format is desired, why not using PNG with maximum
> compression instead of TIFF?

I used LZW (Lempel-Ziv-Welch) compression in this instance - I didn't do a 
size comparison with PNG, though.

> I don't remember any reason for 300 dpi, 600 dpi and a few other
> resolutions to be "special" in any way concerning image files and
> manipulation algorithms...  (except for bein related to the resolution
> of some printing and scanning devices and sometimes explicitly listed in
> program menus for convenience).

400dpi was listed in the scanner menu as an option: I used it as a test on 
the castle, to see whether it would be sufficiently high enough for 
processing tools to be able to remove the half-toning artefacts (the jury's 
still out on this question, however).

Cheers, .....Nick Pelling..... 


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