From: atomas@geloser.login.qc.ca (J-F Bissonnette)
Newsgroups: rec.photo
Subject: Re: Why analyze color on each frame? 
Date: Sun, 27 Sep 92 02:02:16 EDT
Distribution: world
Organization: Gentleman Loser System, Montreal/Qc/Cdn

tonyp@cs.umr.edu (Tony Phillips) writes:

> As an amateur photographer with no room (or money) to build a color darkroom,
> I'm forced to take my film to a processor.  One thing I've noticed that
> happens to my prints really peaves me.  I'd like to know why it happens.
> The problem is color balance.  Why is it necessary to adjust color filtration
> on every frame?  Use a neutral negative to adjust the printer to that roll 
> of film's color differences and also adjust for the batch of paper, but then
> it seems like the lab should just leave the color alone.
> 	Case in point:  I recently took some photographs at the Great Forrest
> Park Balloon race in St. Louis over the weekend.   My prints came back with
> white skies and yellow trees on the pictures where the sky was predominant.
> Other pictures were of friends standing in a field of green grass that was
> printed dull, and the skin tones had an ugly magenta color in them.  I asked
> the lab tech why this occurred and he told me that it was the printer adjusti
> out the over-saturated green.  
> 	Well, I don't WANT this.  I'm gonna start shooting slides (since 
> what's in front of you is basically what you get).  Why should prints be
> any different?
> 
> Thanks for clearing up the matter for me,
 
As a lab tech, I tell you right now that normaly, if the film is not
over exposed or under exposed by more than one or even two stops, the
printer should not make an awfull correction in color.  I work on a 
Noritsu machine and when I have to balance it, I got a special negative
witch as a normal print, an over and an under one.  So when the machine
sees an over negative, it is suposed to make a good print... except 
if the picture is way over exposed... and even then I can usualy make
a good corection (but it usualy affect the contrast).  About your
white sky and yellow trees, every thing depends on your exposition.  
If your camera reads a f:16 in the sky, and theres a reading of f:5.6
on the grass or any other subject, well you wont be able to get both
clear, the difference in contrast is too big.  One of the good 
way to avoid this is to have a spotmeter for making an average 
reading between your highlights and the shadows, but this is 
expensive.  So try to make some other ones withs a different f stop
or different speed, write down what you do and send it to the lab,
then see the diffence.  Finaly, for the magenta faces, well this is
a lab tech mistake (usualy, depending of the machine type).  If
you have a lot of grass in the picture, the printer sensors makes 
a basic correction, but in extreem cases, the correction is too 
big.  The corection is the opposite of the predominant color 
witch is gree when you have a lot of trees and grass.  The opposite
color (you may no it ) is magenta.  When a technician sees such
a print, he is supposed to make a color faillior corection to 
remove the excess of opposite color, your lab tech seem to forget
that.  But notice that there is some machine that do that CF 
corection by themselves...

J.F.
> 

--
atomas@geloser.login.qc.ca
Gentleman Loser System -- Montreal, Qc, Canada