Re: Anyone care to comment?
Re: Anyone care to comment?
- Subject: Re: Anyone care to comment?
- From: Graeme Gill <email@hidden>
- Date: Wed, 22 Sep 2004 11:09:48 +1000
- Organization: Color Technology Solutions
email@hidden wrote:
1/ I've been reading up about how our eyes work. "The biology of
seeing" by Margaret Livingston is a good book to start with.
It validates my personal feeling that 5000K compresses the tonalities
and darkens the display, so that it is harder for our eyes to perceive
in the red part of the spectrum. The cone photoreceptors in our eyes
need a lot of light to perceive color.
Perhaps if it is difficult to match a print to the image on a computer
display, it does help to reduce the visual spectrum. It follows then
that limiting it even further - dark brown sunglasses - should be even
I doubt that "reducing the visual spectrum" (by which I'm assuming you actually
mean reducing the gamut, since the spectrum from a display doesn't change in
extent, just levels if the channel balance is adjusted) is the reason it
is desirable to make a display match the white point of what you want to
reproduce on it. As far as I can gather, reasons are likely to be:
1) Most color correction packages can't handle absolute mode profile
linking for source and destination profiles with different white points
of similar luminance, without clipping the white point.
To properly do an absolute transform from (say) a print profile with a
white point of about D50 to a display setup to have a white point of
D65, you need to scale the brightness of the input down so that the D50
white point fits within the display gamut. This is never something you'd
do when proofing from print input to print output, since "scaling the brightness"
would make the print look washed out, and a poor absolute match (and isn't
very necessary, since the white points are likely to be much closer).
On a display, scaling the brightness down is less of an issue, since there
will be adaptation to the lightness of the scaled white point. This is a
difference between an additive display device and a subtractive one.
If the display is setup to a source profile matching D50 white point (effectively
by turning down the blue channel), then the brightness scaling is being done
by the display, and a normal absolute link will give a satisfactory result
without noticeable clipping of the white point.
2) Within the profiling workflow there may only be access to 8 bit resolution
raster data, so scaling the blue channel down using profiles, throws away
some of the limited available resolution.
By scaling the blue down in the display, or in the RAMDAC tables (which may
have entry values greater than 8 bit precision), this loss of resolution may
be avoided.
3) Much of the clutter around the image you are evaluating is GUI graphics
that is encoded in the application as RGB values, and won't be transformed
through the profile. This means that next to your nice D50 white on the screen,
there is lots of D65 white. Your eyes won't fully adapt to the D50 white,
and the image will look unnaturally yellow.
By making the display have a native white point of about D50, all the GUI
graphics will have the same white point, and there will be no conflict
in adapting to D50.
Graeme Gill.
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