Hi Wayne,
My original question was whether or not I could upgrade the PC Fax driver
that got installed along with other software when I installed my Canon MP730
on my PC? I was hoping that an "upgraded" driver would let me manually
specify Standard, Fine, Grayscale, etc. fax resolutions. Well, I faxed your
thoughtful reply to my post to myself (
www.maxemail.com) by "printing" your
post to the Canon MP730 fax "printer". The very nice result can be viewed
below:
http://www.petersale.com/images/scans/word_fax.tif
Actually, you need to save the sauce and then view it with "Windows Picture
and Fax Viewer" to enjoy the full quality of this fax. In short, it seems
the MP730 fax PC driver usually does a splendid job of automatically
setting the appropriate resolution settings, at least for this Outlook
Express document, and also for jpgs "printed" from Adobe Photoshop. My
problem was that a b&w resolution was chosen by the fax driver when I
attempted to "print" to the MP730 Fax driver from within Adobe Acrobat.
Click below to see what I'm talking about.
http://www.petersale.com/images/scans/mp730_fax2.tif
What I wanted was more like the following
http://www.petersale.com/images/scans/mp730_fax1.tif
but with fewer "dots."
Yes, printing a text source file directly to the fax software is always
better quality than printing it and then scanning it to fax.
All three of your images are 200 dpi line art, which is what fax is. Fax
simply does not know about grayscale. However the one image appears "more
grayscale" because the software created halftones, scanning first in
grayscale and then (because fax requires line art) converted to halftone
patterns of black or white line art dots that similate grayscale, in the same
way newspaper and magazine photos print grayscale using only black ink in
halftone patterns. More black dots is darker gray, few black dots is lighter
gray. You can see this halftone pattern better if the TIF is viewed on the
video screen larger than 100% size.
However the low quality is because the screen for fax is only 200 dpi, where
magazine screens are usually 2400 dpi, so there will be huge differences in
the detail and quality. Fax is simply very low resolution, designed for
speed on the telephone line and cant compete in most other ways. Fine
resolution is "full" 200 dpi resolution, and Normal sends only every other
line, effectively 200x100 dpi. A few fax machines do offer proprietary 300
dpi modes, often called Super Fine, but this is only useful to other similar
fax machines when you know they can do it, and is not usable in the general
case. That telephone time is also 9 times longer than Normal.
If you scan the image in grayscale mode, the fax software has no choice but
to convert it to line art. Often this is done with halftones, but sometimes
simply by threshold, which is the difference in your two cases.
Possibly more than you want to know, but you can convert grayscale images to
lineart halftones manually in Photoshop yourself (so that you have full
control of results), and then simply print that halftoned line art image to
the fax software. Photoshop menu Image - Mode - Bitmap (bitmap means line
art to Photoshop). Then if for fax, Output Resolution is always 200 dpi, by
definition of fax. Then Method is Halftone. Next dialog Frequency, 33 to 45
lpi will likely give your best results for fax. More Frequency lpi gives
more detail, but fewer shades of gray. Less lpi gives less detail, but more
shades of gray. It is a big tradeoff, and which is best depends on the
individual image, if detail or graytones are most important.
Specifically, Resolution/Frequency 200 dpi / 40 lpi = 5 pixels per halftone
cell, or 5x5 halftones, or 26 shades of gray, which is nearly acceptable
sometimes. 33 lpi is likely better for fax in many photo cases, but 45 lpi
may be better for graphics. But if you have photos, fax results are doomed
anyway, and it is much better to instead just use email, why beat yourself
up? It seems a lost cause.
Fax doesnt have to use halftones for this. The other bitmap Methods there
like Dither or Threshold can be excellent too, sometimes better for fax, esp
Dither. All are ways to simulate gray tones with line art density patterns
of black dots. Examining results at more than 100% size will help understand
it. Some fax software does this grayscale to halftone conversion
automatically, with one fixed set of values for all cases.
The resolution of fax is very low, too low for photos. Magazines probably
use 2400 dpi Resolution with 133 or 150 lpi which is 2400/150 = 16 pixels, or
16x16 cells for 256 shades of gray. Detail AND graytones. But 200 dpi isnt
much today, however it works for text.
