DEC scanned documents for Bitsavers (message for Al Kossow)
js at cimmeri.com
js at cimmeri.com
Fri Apr 24 10:13:12 CDT 2015
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.
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