----- Forwarded message from "Jean-Luc Coulon (f5ibh)" <[EMAIL PROTECTED]> -----


I forward this message to the user list as the thread begun there.
I have done a replied to the message I got from Carol addressed to me a
cc to the web list.

Please Carol, don't do "cross-threading" [tm], we become a bit confused
following threads with such pratices.


                - Jean-Luc
From: "Jean-Luc Coulon (f5ibh)" <[EMAIL PROTECTED]>
To: Carol Spears <[EMAIL PROTECTED]>
Subject: Re : Gimp and prepress functions [long]

Le 23.03.2004 22:57, Carol Spears a écrit :
>On Tue, Mar 23, 2004 at 10:29:41PM +0100, Jean-Luc Coulon (f5ibh)
>i wonder how one compensates for the external lighting on the monitor?

The monitor has to be calibrated in the lighting conditions you will  
use it. It is the same for checking the prints. I calibrate the monitor  
for 6500K Colour Temperature and when I need to be very precise in some  
checking I use an external liggting which color temperature is known  
(it does not *need* to match perfectly the one of the display, I use  
"blue" incandescent bulbs which colour temperature is about 5000K).

>i had a chat with a manager of a print shop; he told me that he went  
>an all day conference where he learned that the best way to convert
>one set of colors to another was to let the machine doing the printing
>make the conversion.

If you left the machine to do the job, you are never sure of wht you  
will get. Everything is averaged. i.e. if you have a photo with lot of  
green (forest, grasses), you will get a colour shift to magenta of  
otherwise neutral parts.

>i had a friend who went ahead and bought the full Photoshop (7) for  
>print conversion goodness found within, only to have the printer scold
>her for not using their software.  she paid for their "proper
>i will read this article, but even i can see that during the day, my
>images look vastly different than they do at night on my computer

If you work in the dark, then you have to calibrate your monitor in  
such conditions.

>perhaps it is in your best interests to purchase a devise that will
>change the monitor coloring moment by moment.  even a change of the
>angle of the monitor (physically move your monitor right now and see
>what i mean) will make the colors look very different -- without
>changing the file whatsoever.

LCD (TFT) monitors have their gamma which change drasticly when you  
change the angle of view. (but some very few expensive ones). CRT are  
still better on this point of view. Anyway, a display doesnt have  
steady characteristics and has to be calibrated time to time. Only few  
display has a feeback control for thee electron beam (some Barco made).  
But they are *really* expensive... But sometimes *needed* depending the  
work you have to do. Fine arts professional *do* need a calibrated  

>if it is an issue of not using some rgb values then i think that the
>color dialog will do this.

There are several things: what the data are and how they are displayed  
and/or printed. An uncalibrated monitor will display a wrong colour  
while the RVB data are correct due to its own rendering transfer  
function. Applying the icc profile (hte one from the manufacturer or  
created by yourself with a spetrocolorimeter or at least with a tool  
like lprof under linux which allows you to setu the gamma) will allow  
the display to render the right colour. The data in the file are not  
changed. If you need an other colour space. Then the data has to be  
changed and the colour space data has to be embedded in the picture  
file. sRGB colour space has the minimum_average_commun gammut of most  
the devices. It has been created (mostly by Microsoft) to avoid  
embedding colourspace. sRGB is standard in Windows (so-called)  
operating systems.

>if it is an issue of how the file "appears" i dont know that you can
>accomplish this.  and i use a desktop -- what about people using
>laptops?  they were made for mobility and portability (i think).  how
>many color profiles would it take to make up for the ambient lighting
>moment by moment if you can use your computer just about anywhere in
>this whole big world of ours.

You cannot use a laptop for *photography* processing. You can do  
graphic creation. You can do special effects. You can do web creation.  
But for photography, you *need* a calibrated monitor or you will be  
"blind working".

>i really hope that there is more to this need than this explanation.
>can you all tilt your monitors right now to see what i am saying?

Best regards
                        - Jean-Luc

----- End forwarded message -----

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