Digital BW, The Print

Hello clayton,

Your amazing thing #1 is just what we were talking about a few weeks 
ago when I first started BO printing and had to create a transfer 
curve for the back end to change the "room at atalaya scene" so the 
fireplace would have a printable black and not blank black and 
change the shutters so there was some detail in the slightly darker 
area. (Whew! Long sentence that probable needs puncutation!!) In the 
eamil I sent I said "I have re-read your articles and with the help 
of another group member who dumbed it down for the old man to 
understand. I now use the front end of Gamma Gray 2.2 and have added 
a transfer curve on the back end of 50=55% 70=65% 80=75% 90=85%  to 
get the print to match the screen image." You mentioned that you had 
printed the image just straight and if you had made the changes I 
mentioned yours would have come out differently than mine did. You 
added that the only time I would need a back end curve was to adjust 
for different paper. Evidently my printer is not a very good printer 
for doing these things, but when I made the back end transfer curve 
it brought the lower values up enough that the image as printed 
matched my screen image. And my monitor is calibrated, so I guess 
this transfer curve calibrated the printer to match the screen 
image. WYSIWYG? Maybe we need to talk more often, it seems like we 
both have ideas on this subject. Yours are scientifically based and 
mine are by the seat of my pants.
> 
> -----Original Message-----
> From: Clayton Jones <cj@c...> [mailto:cj@c...]
> Sent: venerdì 14 febbraio 2003 8:30
> To: DigitalBlackandWhiteThePrint@yahoogroups.com
> Subject: [Digital BW] Two Amazing Things
> 
> 
> Hello All,
> 
> I was getting ready to make some prints this evening from an image 
I'd
> previously worked up and considered finished.  After the first 
print I
> felt it needed a tad more contrast, so I decided to use a transfer
> curve until I had it worked out to my satisfaction, before I 
changed
> the image.  After a few trials I ended up changing each end by 1% -
> the 5% point became 4% and the 95% point became 96%.  This added 
just
> the right amount of extra kick it needed.
> 
> I then decided to permanently alter the image by adding the same 
curve
> in a layer, flattening and saving it.  The transfer curves are 
scaled
> in % units and the adjustment curves are in RGB values, so I used a
> calculator to make sure I entered an identical curve (each 1% is 
equal
> to 2.56 RGB units).  
> 
> As I was doing this I was thinking about yesterday's thread where I
> said I could see the difference in a print with as little as 2 RGB
> units change.  That was a general statement from memory and an 
amount
> I felt confident saying in public.  I had never actually done any
> exact testing to see what degree of change could be detected.  I
> realized that my 1% change (2.56 RGB units) had made a clear
> difference in the print.
> 
> While entering the curve points I discovered I could not enter the
> exact values because you can only enter integers, not fractional
> values.  So instead of 2.56 RGB units I had to change the points by
> either 2 or 3 units.  I chose 3 for the dark end (moved the 13 
point
> to 10) and 2 for the light end (the 243 point to 245).  The first
> print came out looking a tiny bit too heavy in the blacks, so I
> changed the dark end to a difference of 2 (13 to 11).  This time it
> was a tiny bit too light  (compared to the transfer curve print 
which
> was a difference of 2.56).  It was still darker than the original 
so I
> decided to stick with that and flattened it and saved the file.
> 
> It suddenly dawned on me that a difference of one half an RGB unit 
was
> detectable in the print.  Including the transfer curve print, the 
95%
> points in the three prints were increased by 2, 2.56, and 3,
> respectively.  The difference in all three prints, while subtle, is
> clearly visible.  That, to me, is amazing.  What an incredible 
degree
> of control we have.  One half RGB unit is equivalent to about .2%
> 
> To have that degree of control with an enlarger we'd have to have 
the
> light stopped down to a 500 second overall exposure for the print
> (over 8 minutes).  This would allow us to dodge or burn for 1 
second,
> giving us the .2% adjustment.  The numbers work out ok, but in
> thinking back to darkroom work, I doubt that burning for 1 second 
out
> of an 8 minute exposure would yield a noticable difference.  
Perhaps
> the paper is not sensitive enough to show it.  Is my thinking off
> here?  Anyway, it's interesting.
> 
> The 2nd amazing thing is when I thought about the fact that I'm
> printing BO, and how the printer changes the spacing between the 
dots
> to get the various shades.  It's one thing to do that at the upper 
end
> where you can see individual dots getting closer or further apart, 
but
> how does it do it down at the dark end?  How in the world does it 
make
> a solid tone, so dark there are no distinguishable dots, a bit 
darker
> when I change a value by a half an RGB unit?  Does it 
still "think" in
> terms of individual dot spacing, all of them ever closer together 
and
> overlapping, or does it know that at some point they are all
> overlapping and it just changes the amount of ink it lays down? 
> However it does it, it's incredible.
> 
> I'm a programmer, and I understand the principles by which all 
this is
> done,  but I'm still in awe of it.
> 
> 
> Regards,
> Clayton
> 
> 
> Info on black and white digital printing at    
> http://www.cjcom.net/digiprnarts.htm 
<http://www.cjcom.net/digiprnarts.htm> 
> 
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