Re: lineart vrs greyscale

Bob van der Poel (bvdpoel@kootenay.com)
Sat, 24 Apr 1999 09:25:09 -0600

Thanks, Nick, for the very good (and fast) explanation. I will fool
around with the brightness settings to see what I can get later today.

Nick Lamb wrote:
>
> > I was scanning some documents last night using my Microtek E3. I figured
> > that since the text was straight black and white that I should use the
> > lineart setting. Even at 300dpi the result was unreadable. Using
> > greyscale produced nice docs.
>
> > So, what's going on? When I select lineart or whatever, I assume that
> > this is setting the scanner to scan in a particular mode...so shouldn't
> > it be able to resolve b/w text better in lineart mode?
>
> The scanner hardware actually resolves greyscale, and lineart mode sets
> a threshold, just like the filter of the same name in e.g. GIMP. So
> the results of the threshold would pick up black-on-white art work while
> ignoring the noise from the grain of the paper, smudges etc. For text
> this is probably not what you want, unless you have an algorithm which
> works only on BW data, perhaps some OCR does this?
>
> To the human eye greyscale will always look better because it reduces
> aliasing. So if you're just going to look at the results (or use an
> algorithm which permits greyscale) you should use greyscale.
>
> The other advantage of line art is that it returns much less data (of
> course 8 times less normally, or better with RLE) and so can be saved
> to a smaller file and transmitted more quickly over SCSI. This might be
> important for scanning A4 documents at high resolution quickly.
>
> NB. You should be able to get *acceptable* results if you can tune the
> brightness or threshold parameters for the scanner hardware. I can get
> readable text from 400dpi lineart with the ScanJet IIc here.
>
> Nick.
>
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