[argyllcms] Re: inter-instrument matching tables
- From: Gerhard Fuernkranz <nospam456@xxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 06 Jan 2012 21:57:24 +0100
Am 22.11.2011 00:57, schrieb Gerhard Fuernkranz:
Am 20.11.2011 01:42, schrieb Roberto Michelena:
Attached a file with a variety of measurements from a P2P25x target
(idealliance) ...
Thanks, Roberto.
I'll take a look at your data - a detailed investigation make take a while,
though...
After a first brief inspection it seems that
* the data from the same instrument, but for different calibration standard
can be mapped to each other with virtually no errors.
* DTP70 readings can be estimated from DTP70_UV readings (or vice versa)
with an estimated error of about 0.1 dE RMS
* I1 readings can be estimated from DTP70 or TDP70_UV readings (or vice
versa) with an estimated error of about 0.3 dE RMS
I have done some more investigations with the data in the meantime, and I have also drafted two
programs "scmxmake" and "scmxapply" which create and apply a (media-specific)
spectral correction matrix from/to spectral .ti3 files. They are based on the on-board methods
available in Argyll and thus fit with the Argyll framework (which made the implementation a bit
tedious and also more CPU-hungry, compared to simply prototyping the underlying maths in a language
like GNU Octave). A patch to Argyll V1.3.5 is attached (I hope it compiles and runs under Windows
as well, as I have only tested on Linux). Maybe you want to give it a try...
Usage: scmxmake [options] input1.ti3 input2.ti3 output.scmx
-v Verbose mode
-O Use OLS instead of TLS
-p num_pc Choose number of principal components to use
for the PCR regression. If not specified or <= 0,
then the optimal num_pc is estimated by bootstrap
cross validation.
-B samples Choose number of bootstrap samples to to use
for estimating the error. More samples are better,
but computationally more expensive.
<samples> must be either 0 or >= 100.
If samples = 0, then errors are not estimated.
-i illum Choose viewing illuminant:
A, C, D50 (def.), D65, F5, F8, F10 or file.sp
(Only used for calculation of error estimates)
-o observ Choose CIE Observer for spectral data:
1931_2 (def), 1964_10, S&B 1955_2, shaw, J&V 1978_2
(Only used for calculation of error estimates)
input1.ti3 1st measurement file
input2.ti3 2nd (reference) measurement file
output.scmx Correction matrix file. The correction
estimates input2.ti3 from input1.ti3.
Usage: scmxapply corr.scmx input.ti3 output.ti3
corr.scmx Correction matrix file
input.ti3 Measurement file
output.ti3 Converted measurement file
Example usage for i1 vs. DTP70:
* Obtain "training-chart-i1.ti3" and "training-chart-i1.ti3" by
measuringa printed, representative test chart with both, i1 and DTP70.
* Compute correction:
scmxmake -v training-chart-i1.ti3 training-chart-DTP70.ti3
corr_i1_to_DTP70
-> creates "corr_i1_to_DTP70.scmx"
* Now read other chart(s) (but same printer, ink, paper, etc.) with the i1,
resulting in say "chart2-i1.ti3".
* Apply correction in order to estimate the readings which would have
been obtained when reading this chart with DPT70 instead of i1:
scmxapply corr_i1_to_DTP70.scmx chart2-i1.ti3 chart2-DTP70.ti3
Regards,
Gerhard
Other related posts:
