Color profiles for attached monitors
Color profiles for attached monitors
- Subject: Color profiles for attached monitors
- From: Robert Ralston <email@hidden>
- Date: Mon, 21 Nov 2005 15:57:13 -0800
Title: Color profiles for attached
monitors
The behavior of
color profiles for external devices seems mysterious in a number of
ways.
Setup:
2 Apple laptops (800 MHz G4 Titanium, 1.67 GHz G4 PowerBook 15").
Both were connected to an external Dell 1800 Flat Panel Display via a
VGA cable connected to an Apple DVI-VGA dongle. Both laptops
running Tiger with all updates to date.
Behavior:
With the external monitor attached, you get a suggested color profile
for it in /Library/ColorSync/Profiles/Displays. In this particular
case, The profile is called "DELL 1800FP-283835D5.icc. With some
attached devices, like older projectors, one gets a generic sort of
label, like 'VGA Display' or 'LCD Projector'.
If the VGA cable is
disconnected, the laptop screen stays the same and the profile is
still present as a file. After a Detect Displays, the Dell color
profile is gone.
If you reconnect the
VGA cable, there is no picture on the Dell, nor color profile for it
until a Detect Displays. Then the profile is back.
If you disconnect the DVI dongle, the laptop screen goes to
blue before going back to an image, and the Dell profile is gone.
Reconnecting the DVI dongle gets back the external image and the Dell
profile.
If you move the color profile from its location, the suggested
profile for the external monitor changes to "Generic RGB Profile"
under the Color tab for that device in Displays Preferences.
Detect Displays does not bring back the Dell profile. You must
restart or disconnect/reconnect the DVI dongle to get the Dell profile
back.
You can copy the Dell profile file, so it seems like it really
is a file written to disk, even though a temporary one.
Questions:
1.
What is
generating this Dell color profile?
a.
One theory
is that it is being transmitted over the DDC lines from the external
device. Being a text file, OS X then can easily write
it to disk.
b.
Another
theory is that the external device sends in its descriptive data,
again via the DDC lines, and then OS X constructs an appropriate color
profile from that data. Indeed, the copyright on this external profile
is Apple when examining it with ColorSync Utility.
2.
How is a
DVI dongle disconnect triggering the OS? What pin(s) are
initiating action from the OS?
3.
Why
doesn't a Detect Displays bring back the Dell profile when the
original one is moved. Doesn't the Detect Displays trigger a DDC
inquiry to the external device?
4.
The Dell
color profile shows up only for the external device, never for the
laptop display. Other display profiles we copy on show up for both the
external device and the laptop display. How is a profile tagged
so that it shows up for only the internal device or the external
device?
5.
Does the
suggested profile for the laptop ('Color LCD') come from the EDID
which can be read in Open Firmware (by looking at the device tree and
navigating to the video 'card)? That sort of makes sense, i.e.
the OS asks and finds out what are the characteristics of the laptop
display from firmware.
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