[argyllcms] Re: Backlit media
- From: Alexey Gribunin <Gribunin@xxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Wed, 6 Apr 2022 11:58:22 +0300
Hello Roger!
Yes, profiling "backlit media" is possible with ArgyllCMS with various
instruments as Graeme wrote.
Please take a look on my 5 years old letter below, there are some my
keypoints there.
Nowdays I'm using flat LED ceiling light as "light table".
I'm reading testchart with i1Pro3 spot by spot.
It takes 1 hour to measure 480 patches testform (436 unique color
patches and 44 white patches for linear spectral correction of light
drift). I found that 480 patches is enough to get good profile.
With i1Pro2 it takes 30 minutes because of lower measurement time, but
it gives higher noise. This was described by Graeme in reply to my
letter "Slow measurements in transmission mode with i1Pro3" to this list
in August 2021.
Best regards,
Alexey Gribunin.
On 05/04/2022 20:37, graxx@xxxxxxxxxxxx wrote:
Just curious whether argyll has any capabilities with regards to
profiling ‘backlit media’?
I was looking at X-Rite iO Table / i1profilerPro3 “solution” and the
process is quite involved. First, measure a “light table”, thin enough
to place on the surface of the iO table, to sort of “flat-field” it (I
guess), and then measure some target in patch mode.
Any thoughts? Suggestions? Experiences?
/ Roger
=========================
On 23/11/2017 09:15, Tony Mah wrote:
> Wondering if this is possible?
> I have an NEC monitor with a 3d LUT set at D65, could I:
> 1. print a sheet of backlit film with color patches
> 2. display white on the monitor
> 3. put the film on my calibrated monitor
> 4. use my i1pro and measure each patch like a piece of paper
For sure, it's possible!
I'm making such profiling from time to time and the quality of such
profiles seems to me almost perfect. It gave very good visual gray
balance, smooth gradients and perfect details in highlights and shadows.
I think it's almost all we want from icc profile for photo reproduction :)))
On 23/11/2017 15:17, Graeme Gill wrote:
> it's much less important what the color temperature is,
> than how spectrally continuous it is, and how uniform it is.
Absolutely agree with Graeme, the color temperature itself is not so
important. I would say, the most important things are uniformity and
stability.
> A good quality light box may be a better bet, or a second hand DTP41T.
In the past I used LCD monitor without matrix (it was damaged, but lamp
itself was good, so I just remove the matrix and used it as a light
table). But the uniformity and stability is not very good, so it was
necessary to calibrate i1Pro every few patches.
Now I'm using iPad (!) and found it much more stable (auto-brightness=off).
But calibration every 10-15 patches is also highly desirable. It's
necessary to get really repeatable and reliable values.
I'm calibrating device during measurements in two different ways:
1. I'm making ArgyllCMS native calibration every 75 patches.
2. I'm measuring white patch every 15 patches and making linear spectral
correction afterwords in EXCEL.
Best regards,
Alexey Gribunin.
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