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

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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