10 okt 2005 kl. 10.57 skrev Qkano:
<i was wondering...if you were to have digital B&W images coming
from scanned media what would you choose from? B&W Negegative or
Color Slide for Digital B&W?
Does having 3 different channel info to tinker with offer an
significanr advantage?>
Kostas
Absolutely no question in my mind.
If I scan B&W negs - or positives - I prefer to have all three
colur channels independantly even though they are supposedly
supplying the same info. The difference is the noise level and
resolution may not be the same in all three and you get to choose.
If you scan "in B&W" on a colour scanner you are in essence letting
the scanner manufacturer decide for you.
<as an aside...
Starting froma greyscale image and converting it to RGB, is making
channels into layers and tinkering with them (including blending
modes) any good?>
Can't see much point in that. You may as well just duplicte the
layers? The only time I split greyscale into channels and
recombine is for making anaglyphs.
Bob
There is a noticeable difference in noise level between channels, but
there are a couple of comments to be made:
1) This difference is a property of the scanner itself, so once you
find the "best" channel, it will remain best for all negatives
thereafter (I´m talking about traditional B/W silver film, not
chromogenics; no experience with them).
2) There may well be a difference in sharpness as well (possibly due
to the scanner optics being less-than-apochromatic). I´ve seen people
arguing that the least noisy channel is also the least sharp one; don
´t know from own experience.
3) True scanner noise seems far less significant than actual film
grain with all films I´ve scanned (I don´t shoot very slow films),
and film grain looks similar in all three channels. For this reason,
I´ve actually ended up scanning as B/W anyway; in the finished prints
I see film grain OK, but the actual difference between channels is no
longer noticeable. I use a Minolta 5400 for 35 mm, and an old Epson
2450 flatbed for 120, and always VueScan software, never the
manufacturer supplied junk. Quite possibly my conclusion isn´t valid
for other setups.
4) ALWAYS scan max resolution, even if you don´t really need it for
the final print! Both definition and granularity is FAR better if
you scan at 5400 dpi and then downsample to 2700 than you get from a
2700 scan (Google for the term "grain aliasing" if you want a lot of
heated argument about a possible explanation; I´m doubtful about
parts of that explanation, but the effect is very real indeed).
5) ALWAYS scan 16 bits if at all possible! You will want to do a lot
to the tonal scale of the raw scan, and this is a lot easier to do
without posterizing in the shadows & c if you have 16 bits to start
with.
Yes, following both 4) and 5) does give you a 4 x 4 = 16 times as big
raw scan file, but so what? I never save raw scans anyway, as long
as I have the negatives; one should get better at scanning with time
and practice, and thus it is better to make a new scan if you need it
3 years from now than to dig up an old jumbo file that just wasn´t as
well made as you can accomplish after 3 years of experience...
Per
Per Öfverbeck
http://foto.ofverbeck.se
"In a world without walls or fences, who needs Windows or Gates"
