DEC scanned documents for Bitsavers (message for Al Kossow)

Johnny Billquist bqt at
Fri Apr 24 10:03:22 CDT 2015

On 2015-04-24 17:00, js at wrote:
> On 4/24/2015 9:46 AM, Paul Koning wrote:
>>> On Apr 24, 2015, at 10:40 AM, js at wrote:
>>> On 4/24/2015 8:48 AM, Noel Chiappa wrote:
>>>>      >   From: shadoooo
>>>>      >   I'm scanning at 600dpi grayscale, lossless compression.
>>>> I've been scanning a few things too, and I found that 600dpi grayscale
>>>> produced absolutely enormous files (many, many MB's per page, for
>>>> prints), no
>>>> matter what I tried to do, compression-wise.
>>>> 600dpi black and white, followed by saving as TIFF's with CCITT Group 4
>>>> compression, produced immensely smaller files (small 100's of KB's
>>>> for the
>>>> same pages), and they are quite readable (even the fine letter seems
>>>> to be
>>>> readable - b/6 is quite distinguishable, etc).
>>> While smaller, I've always found 1 bit b/w scans to be nightmarish to
>>> read (too much font detail is sometimes lost), and forget about
>>> grayscale pictures and diagrams coming across intact.  Grayscale is
>>> best.  The problem comes in overdoing the DPI.  Even 90 dpi is good
>>> enough.  150, more that sufficient.  300 or 600, total waste, but
>>> they are (obviously) the most accurate renderings.
>> I would not call 90 dpi “good enough”.  The professional printing rule
>> of thumb is that for an n grayscale dots per inch halftone image you
>> need 2n DPI resolution.  So 90 dpi is, at best, low grade newspaper
>> resolution.  A standard commercial grade scan for good quality
>> printing is 260 dpi or so — which means 300 is certainly a fine
>> choice.  150 or below may well be acceptable if that’s the best you
>> can get, but you’re definitely compromising image quality if you do that.
> Why don't you actually try it.   Also, I'm assuming reading on a screen
> (where I read most of my vintage manuals) vs. re-printing.  My screen
> resolution is 90dpi.  Anything over that is pure waste.   Maybe you have
> better eyes than I do, but I can't discern image quality over 100-200dpi
> for printing.

That seems like a weak argument. While looking at documents on a screen, 
I often magnify them to see details. So a higher resolution of the 
source material than what the screen offers is very meaningful.


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