DEC scanned documents for Bitsavers (message for Al Kossow)

[Paul Koning]

> 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.

	paul