Using a different calibration tile

[Stefan Hegnauer]

Hi there,

I bought an i1pro rev. D a few years ago (2nd hand, S/N 301759) and used it
for emissive measurements (display calibration, LED & lighting spectra
etc.). Works perfectly so far.

Now I would like to use it for reflection type measurements as well. The
reflection calibration tile that came with it has a different serial number
though (S/N 132782) and while it works somehow – neither Argyll nor the OEM
tools reject it - I have reason to believe that the calibration data within
the i1pro is not exactly correct WRT the actual tile. E.g. there are dips
and peaks at certain wavelengths over a variety of different targets that
IMO can only be attributed to flaky calibration based on reflectivity data
that does not match the calibration tile I have. This is even more apparent
when using high resolution mode.

Assuming that I can measure the true tile reflection properties for 45°/0°
at a fine enough wavelength spacing and with sufficient accuracy – how could
I use such data to correct the calibration of the i1pro for reflective
measurements? From the Argyll source code I reckon that the calibration
data is read at the beginning and then cached in a file for subsequent use –
could this be utilized somehow? Thought I would ask before starting to
tamper with the sources … especially as I am more a HW guy (EE).

Thanks and best regards
Stefan

[Ernst Dinkla]

Stefan,

You could start with cleaning the inside and thin glass filter in the
cone of the i1Pro from any paper lint etc. The cone can be taken off by
turning it but make sure it does not deform as it becomes more difficult
to get it off. There is a kind of trick to it I can not describe.

[Stefan Hegnauer]

Thanks Ernst.

While it certainly helps to get the best out of any given instrument, it
does not provide new calibration data. It's the latter that I'm looking for
- how to use non-built-in tile calibration data.

Cheers
Stefan

-----Original Message-----
From: argyllcms-bounce-***@public.gmane.org [mailto:argyllcms-bounce-***@public.gmane.org]
On Behalf Of Ernst Dinkla
Sent: Sonntag, 1. Dezember 2013 19:39
To: argyllcms-***@public.gmane.org
Subject: [argyllcms] Re: Using a different calibration tile

Stefan,

You could start with cleaning the inside and thin glass filter in the cone
of the i1Pro from any paper lint etc. The cone can be taken off by turning
it but make sure it does not deform as it becomes more difficult to get it
off. There is a kind of trick to it I can not describe.

--
Met vriendelijke groet, Ernst Dinkla

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2012: 500+ inkjet media paper white spectral plots.

[Nikolay Pokhilchenko]

Just build your own filter file and apply it at every reflective measurement without changing the code. The filter should correct any difference between correct and current calibration data.
It will be interesting if you provide calibration tile measuremets by both instrumets: i1Pro and reference spectro. The correction filter can be build by division reference spectrum by measured spectrum. It should be quite simple and convenient. Do not forget to average several measurements before division.

Post by Stefan Hegnauer
Thanks Ernst.
While it certainly helps to get the best out of any given instrument, it
does not provide new calibration data. It's the latter that I'm looking for
- how to use non-built-in tile calibration data.
Cheers
Stefan
-----Original Message-----
On Behalf Of Ernst Dinkla
Sent: Sonntag, 1. Dezember 2013 19:39
Subject: [argyllcms] Re: Using a different calibration tile
Stefan,
You could start with cleaning the inside and thin glass filter in the cone
of the i1Pro from any paper lint etc. The cone can be taken off by turning
it but make sure it does not deform as it becomes more difficult to get it
off. There is a kind of trick to it I can not describe.
--
Met vriendelijke groet, Ernst Dinkla
http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2012: 500+ inkjet media paper white spectral plots.

[Ernst Dinkla]

Post by Stefan Hegnauer
Thanks Ernst.
While it certainly helps to get the best out of any given instrument, it
does not provide new calibration data. It's the latter that I'm looking for
- how to use non-built-in tile calibration data.
Cheers
Stefan

Stefan,

Aging and manufacturing differences between individual i1 calibration
tiles is just one thing in my opinion. I guess the calibration tile
spectral plot you have was made with the i1 calibrated on the tile you
suspect. Where is the flaw, in the aged i1, in the wrong and very aged
calibration tile? My near 4 years old i1 has a serial number 343367.

Even with data from another i1 calibrated on its own calibration tile
and measuring your calibration tile it will not be easy to get an
objective reference you can rely on for measurements beyond the whites.
Hence my advice to clean the optic path first as I think that could be
the more important step right now. After that a set of color calibration
tiles and one other i1 that is new or had its factory calibration
recently. Like my DIY set of acrylic tiles I measured right after my new
i1 arrived. It will be a complex compensation filter. A calibration by
the factory when too much deviation is observed is inevitable one day.
My guess is that both the tile and cone will be replaced, cheaper than
cleaning it.

[Graeme Gill]

Post by Stefan Hegnauer
Now I would like to use it for reflection type measurements as well. The
reflection calibration tile that came with it has a different serial number
though (S/N 132782) and while it works somehow – neither Argyll nor the OEM
tools reject it - I have reason to believe that the calibration data within
the i1pro is not exactly correct WRT the actual tile. E.g. there are dips
and peaks at certain wavelengths over a variety of different targets that
IMO can only be attributed to flaky calibration based on reflectivity data
that does not match the calibration tile I have. This is even more apparent
when using high resolution mode.

Hi,
what does the reflectance spectrum of something like polystyrene foam
or Tyvek look like ?
You could also compare the reflectance spectrum of the tile measured with the
i1pro and your reference instrument to see what the error is.

Post by Stefan Hegnauer
Assuming that I can measure the true tile reflection properties for 45°/0°
at a fine enough wavelength spacing and with sufficient accuracy – how could

The internal reference is 380 to 730 nm at 10 nm.

Post by Stefan Hegnauer
I use such data to correct the calibration of the i1pro for reflective
measurements? From the Argyll source code I reckon that the calibration
data is read at the beginning and then cached in a file for subsequent use –
could this be utilized somehow?

Not easily - it's not cached in a file. Ideally you could re-write the
instrument flash to store a new reference. An alternative would be some
sort of hack to substitute the contents of an .sp file for the
white reference reading. Look in i1pro_imp.c in i1pro_imp_init()
for where white_ref[0] is set.

Graeme Gill.