;-) Clearing the snow from my glasses, I saw Shawn T. Rutledge typed:
>JPEG is a bad idea for anything other than photos. It works best with subtle
>color variations, and tends to make a mess of sharp details.
Righto you are on this count.
>> Actually, 300 is the max without interpolation. Stuff that's truly B&W
>> should be scanned in B&W mode. The problem is that grayscale picks up
>> variations in print strength, smudges, etc. B&W says "This dot is more
>> than x dark, it's black. This dot is less than x dark, it's white."
>
>That's good advice; however I think in theory the results are equivalent if
>you first scan in grayscale, then use Photoshop to convert to B&W with the
>default threshold. But Photoshop also lets you adjust the threshold when
>converting to B&W, rather than leave it up to the scanner, and you can tweak
>it to better compensate for the effects of old yellowed paper.
Well, Photoshop is *way* too expensive for my blood... I like to use Paint
Shop Pro. One thing I do (for a small number of documents) is scan it in
with 256color B&W, then use the color exchanger with a threshold of 20 or
so, and make all the "near-whites" in the background to white, and all the
"near-blacks" to black. I could show this easier than speak it...
Why I do this: Reason 1: it makes a better looking scan, and besides, PSP's
color reduction algorithms are really great, so reducing the scan to 16
colors comes out top-notch. Reason 2 below.
>B&W images also compress astonishingly well with GIF, which is lossless and
>thus preserves sharp details well. The good compression is due to the large
>amount of white space in typical schematics and drawings.
Have you actually checked this? GIF's do compress well, and you are correct
on loseless... but if you are just GIFfing the scans, they do *not*
compress well. GIFs are just RLE compressed (That's Run Length Encoding
for all you non-gfx types out there) and if you don't have large blocks of
the exact same color, you'll get very poor compression. That's why I do
what I do above... making sure the "near-whites" and "near-blacks" are
solid improves the compression 3 or 4 fold, reducing the color depth to 16
helps heaps as well (while still giving you "anti-aliasing" for readability).
Oh, and at least with Photoshop 4.0, it's stock JPEG encoding sux rox.
Badly. (I was too scared to try the GIF encoding... especially with
transparency). PSP is strides ahead on it's format interchangability.
Anywho, just my thoughts on the subject.
HTH,
Roger "Merch" Merchberger
--
Roger Merchberger | If at first you don't succeed,
Owner, MerchWare | nuclear warhead disarmament should
zmerch_at_northernway.net | *not* be your first career choice.
Received on Wed Apr 01 1998 - 01:01:02 BST