Since my monitor is set to sRGB (which fairly closely matches the output of my
printer) all your images should display about the same. They do not, so I can
only conclude that there is something strange about them (like maybe they are
adjust to to show what the person is trying to show no matter how they are
viewed). Which to me means they prove nothing whatsoever.
--
David Mann wrote:
On Jun 20, 2004, at 2:57 AM, graywolf wrote:
Well, there are certain laws of physics involved here. Reflected light
images (prints) will never match transmitted light images.
Yes, you are correct here. That's the whole basis of the digital colour
workflow.
The worst thing is that with prints you have absolutely no control over
the lighting conditions under which they'll be viewed. Look at a print
under sunlight, then take it inside under fluorescent lighting...
"white" is then defined as "the same colour as the light source" :)
I managed to find a source of daylight balanced tungsten bulbs (now my
local hardware store has them, too). These are standard filament lamps
with blue-tinted glass to compensate for the low colour temperature. I
find them quite useful when trying to do colour matching but I don't
claim them to be exact references. They're too cheap and I'm not
running them from a tightly regulated power supply.
sRGB is designed to approximate reflected light imaging.
Not entirely. sRGB was designed to approximately match the capability
of computer screens.
Quoted from MS's sRGB article:
http://www.microsoft.com/whdc/device/display/color/sRGB.mspx
"From the spectral and colorimetric characteristics of these phosphors,
a standard known as sRGB was proposed and adopted by a number of
companies such as Hewlett-Packard and Microsoft."
This is all very well, but later in their article they attempt to
justify sRGB at the printing stage:
"The gamut issues are also of concern to many. They claim that the sRGB
gamut is too limited and hence "clips" their output device's ability to
reach its full potential. This is only true if one permits this to be
the case. For example, in Figure 3, a gamut of the venerable Canon
CLC500 color copier/printer is shown along with sRGB and the old RGB
realized on the first PC color monitors. Note that while some of the
cyan colors are limited by sRGB, the brightest greens and reds are
output device limited, not sRGB limited."
The third sentence nearly made me fall off my chair the first time I
read it. If your hardware has a greater colour gamut than your working
space can represent, you're using the wrong hardware?!?
BTW the Canon CLC500 was introduced in 1989. Yes, 15 years ago.
http://www.canon.com/about/history/table08.html
I just downloaded the Epson 2200 with Premium Semigloss profile. The
printer's gamut is mainly defined by its inks, which are of course CMYK
based (the printer driver does the RGB to CMYK conversion
behind-the-scenes). The result is that sRGB greatly exceeds the
printer's capabilities for pure red/green/blue, but the handling of
cyan, magenta and yellow is grossly inadequate. In fact, even Adobe RGB
is a bit limited if you wanted to extract every last drop of performance
from the printer.
OK I just did some comparative plots:
Printer (grey) against sRGB IEC61966-2.1 (coloured):
http://www.bluemoon.net.nz/temp/epson_srgb.jpg
Printer (grey) against Adobe RGB 1998 (coloured):
http://www.bluemoon.net.nz/temp/epson_adobe.jpg
Printer (grey) against EktaSpace (coloured):
http://www.bluemoon.net.nz/temp/epson_ektaspace.jpg
And lastly,
Printer (coloured) against the massive overkill that is ProPhoto RGB
(grey):
http://www.bluemoon.net.nz/temp/prophoto_epson2.jpg
You can see that when the working space is big enough to encompass the
entire CMYK gamut of the printer, the RGB channels are suddenly _way_
bigger than they need to be. This can lead to posterisation.
Getting back to digital minilabs, AFAIK they work entirely as RGB
devices so the plots above don't apply :) The only minilab profiles I
have on-hand are totally rubbish so I can't make a good comparison.
Once again, the above is just theory. Take it with a grain of salt.
Cheers,
- Dave
http://www.digistar.com/~dmann/
--
graywolf
http://graywolfphoto.com/graywolf.html
