Monitor correction chart?

[Peter]

On Sun, 7 Aug 2005, Walter Dnes wrote:

> On Sun, Aug 07, 2005 at 08:44:18PM +0300, Peter wrote
>
>> There are ICCM color profiles for monitors. I am almost sure that
>> higher end X servers support this. But I have seen no trace of that
>> in XFree86.
>
>  It shouldn't matter what OS is running.  It should be colour on a
> piece of paper versus colour on a screen.

If you calibrate the screen to the printer output all your edited files 
will only print right with your printer, with the paper you are using, 
and likely only until you change ink or toner. However this is the most 
straightforward way to do it for a hobbyist who will never take his 
retouched photos to a digital printer. This is the worst way to do it.

The goal is not to match the printer to the screen but to match the 
screen to the absolute colors. Then the printer is separately matched to 
absolute colors. Macs have all the necessary correction tables installed 
and usually you only need to choose the right one for your hardware. The 
PC is way behind it in this respect.

Something has to fix it in real time. The something is the video driver 
in Windows, and it should be the X server in Linux. Or the application. 
Higher end video card drivers have color profile editing capability at 
least under Windows.

I goofed when I wrote ICCM, it's ICC, from here: http://www.color.org/ 
They have a number of higher level tutorials. Here are my 'low tech' 
means to achieve what you seek (both methods are tested):

One way to do it is to get hold of a color calibration slide or chart 
(any camera shop should have one). Put it on a lightbox, next to the 
monitor in a room with subdued light of the same color as the lightbox's 
(subdued skylight reflected off whitewashed walls is about right). Then 
adjust the color profile of the monitor until you can see no difference 
wrt. the chart/slide. This is best done with alternating color bars and 
grayscale log charts.

Another less onerous way would be to get hold of a chart's file (pdf 
works great, pdf colors are accurate) and take it to a good (new, high 
quality machines) digital printer's and print it on photo paper. That 
and the correct light source should be able to replace the professional 
chart and lightbox in a pinch.

Then start printing the chart on the printer and adjust the printer's 
color profile until that shows no differences either (using the same 
light as above). Unfortunately you will be wasting a lot of ink with 
this. You could save some by using a colorimeter to measure the color on 
the paper and dial precise changes into the printer color profile, thus 
achieving rapid correction. Offset printing machines use online 
colorimetry and tweak the printing process in real time to obtain 
constant calibrated colors (these machines print most glossy magazines 
and color advertising leaflets and brochures). A handheld colorimeter 
can be borrowed from a photo shop.

>> LCD monitors very rarely manage to render colors with sufficient
>> precision for photo work. Move your head a little and the colors
>> shift.
>
>  It's not as bad as it used to be.  Angle of view is a bit wider now.

A color editor (person) will claim to be able to discern 1-2% color 
saturation change on a screen. The saturation changes more than that 
when you move your head with a lcd screen. Therefore they don't like it.

Peter
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