DEC scanned documents for Bitsavers (message for Al Kossow)

[js at cimmeri.com]

On 4/24/2015 10:03 AM, Johnny Billquist 
wrote:
> On 2015-04-24 17:00, js at cimmeri.com 
> wrote:
>>
>>
>> On 4/24/2015 9:46 AM, Paul Koning wrote:
>>>> On Apr 24, 2015, at 10:40 AM, 
>>>> js at cimmeri.com 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.
>
>     Johnny

Again, TRY it.   Unless you need to 
magnify things 10-20x the original, 
100-200 is more than sufficient *in 
practice* for most purposes.

Despite the differences in opinion on 
*perceived* DPI, the actual thrust of my 
argument here is that it's far more 
important to preserve the _grayscale_ 
quality of a document -- especially for 
those that have photos pictures, 
diagrams -- than any excessive DPI.

- J.