Camera Color Calibration II (used as colorimeter?)

 	This past thread got me thinking about something that came
up 
awhile back.  I'm just querying again to see if there's been
any progress 
on it.

 	How feasible would it be to use an IT8 target to calibrate
a 
decent camera (i.e. manual exposure, RAW capture), and then
turn around 
and use that to calibrate a computer monitor?  I tried
awhile back, but 
got bogged down trying to do the necessary table flipping.

 	Seems like it could be a viable method of generating
profiles 
under linux where calibration hardware is tough to come by
and expensive.

?

-Cory

-- 

************************************************************
*************
* Cory Papenfuss, Ph.D., PPSEL-IA                           
           *
* Electrical Engineering                                    
           *
* Virginia Polytechnic Institute and State University       
           *
************************************************************
*************


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          How feasible would it be to use an IT8 target to
calibrate a 
  decent camera (i.e. manual exposure, RAW capture), and
then turn around 
  and use that to calibrate a computer monitor?  I tried
awhile back, but 
  got bogged down trying to do the necessary table
flipping.

The big problem in the approach you describe isn't inverting
the tables
- that's certianly confusing but can be figured out.  It's
accounting
for the lighting on the IT8 - you need a controlled light
source to make
a meaningful profile.  When you did this, what light source
did you use
to illuminate the IT8, and what you were thining about how
that related
to the white point of the display?

I have found that when I take pictures of displays they
often come out
badly.  But I haven't tried with a tripod and a longish
exposure, to get
well past the refresh rate.

But, I think that what you suggest is doable, and you may
want to check
out http://lprof.sourceforg
e.net/ as a starting point or a framework for
your efforts.



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On Fri, 19 Oct 2007, Greg Troxel wrote:

>          How feasible would it be to use an IT8 target
to calibrate a
>  decent camera (i.e. manual exposure, RAW capture), and
then turn around
>  and use that to calibrate a computer monitor?  I tried
awhile back, but
>  got bogged down trying to do the necessary table
flipping.
>
> The big problem in the approach you describe isn't
inverting the tables
> - that's certianly confusing but can be figured out. 
It's accounting
> for the lighting on the IT8 - you need a controlled
light source to make
> a meaningful profile.  When you did this, what light
source did you use
> to illuminate the IT8, and what you were thining about
how that related
> to the white point of the display?
>
> I have found that when I take pictures of displays they
often come out
> badly.  But I haven't tried with a tripod and a longish
exposure, to get
> well past the refresh rate.
>
> But, I think that what you suggest is doable, and you
may want to check
> out http://lprof.sourceforg
e.net/ as a starting point or a framework for
> your efforts.
>
 	Oh yeah.... I think that was where I'd discussed it in the
past. 
Whoops.

-Cory

-- 

************************************************************
*************
* Cory Papenfuss, Ph.D., PPSEL-IA                           
           *
* Electrical Engineering                                    
           *
* Virginia Polytechnic Institute and State University       
           *
************************************************************
*************


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On Friday 19 October 2007 07:47:10 Cory Papenfuss wrote:
> On Fri, 19 Oct 2007, Greg Troxel wrote:
> >          How feasible would it be to use an IT8
target to calibrate a
> >  decent camera (i.e. manual exposure, RAW
capture), and then turn around
> >  and use that to calibrate a computer monitor?  I
tried awhile back, but
> >  got bogged down trying to do the necessary table
flipping.
> >
> > The big problem in the approach you describe isn't
inverting the tables
> > - that's certianly confusing but can be figured
out.  It's accounting
> > for the lighting on the IT8 - you need a
controlled light source to make
> > a meaningful profile.  When you did this, what
light source did you use
> > to illuminate the IT8, and what you were thining
about how that related
> > to the white point of the display?
> >
> > I have found that when I take pictures of displays
they often come out
> > badly.  But I haven't tried with a tripod and a
longish exposure, to get
> > well past the refresh rate.
> >
> > But, I think that what you suggest is doable, and
you may want to check
> > out http://lprof.sourceforg
e.net/ as a starting point or a framework for
> > your efforts.
>
>  	Oh yeah.... I think that was where I'd discussed it
in the past.
> Whoops.
>
> -Cory

There is an entry on the Scribus Wiki that details how to do
this.  But even 
though they got it to "work"  the results were not
so good for the darker 
tones.  So this appears to be of limited utility.

One other thing to consider.  LProf and ArgyllCMS now
support a wide range of 
measurement devices.  So your assertion that measurement
devices under linux 
are tough to come by and expensive is no longer true. 
Currently supported 
less expensive devices include the EyeOne Display series
(original, 2, Lt and 
other variants) and the DTP-94.  There will soon be support
for the Spyder 2 
and the Huey (although there are some issues with the HID
interface on Linux 
that may cause Huey support to be delayed).  In other words
you can now use a 
number of available and inexpensive meters on *nix platforms
and soon almost 
every available device available will be supported.

In fact I have an OEM agreement with X-Rite for EyeOne
devices and if there is 
interest I can get these and sell them at a discount.  But I
have to order 
these in larger quanities and I would need to have enough
committed buyers to 
do a large enough order to do this.   EyeOne Display Lt's
are going for about 
$130 to $140 plus shipping on the net.  I think I could sell
EyeOne Display 
2's for $110 plus shipping if there was enough interest.

Hal

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