Message
Linearization with scanner
2015-09-12 by unesco18@...
Just my first post here :-).
I have just installed QTR to have a try with BW printing against ABW on my 3880 (Windows) and try to get best possible results. I really like the prints but because of various papers I use I really would like to optimize each paper.
I tried with Tecco baryt papers as well as with Tetenal regular ones (all PK). Because I have no direct access to densitometer as well as to spectrophotometer I used the procedure with scanner described on QTR web page pdf. I have Q13 target and Epson V500 scanner.
I printed dedicated 21 step wedge tiff (there is 15% dot gain profile embeded) through QTR using PK raw neutral profile and scanned both as described in the document (300 dpi, 16 bit to Epson sRGB, all whistles swiched off). Then run the PS script included which finished with Lab .txt file. Then pasted L values to linearization for the profile I used for printing an saved. Scanner quality is ok, all darks easy to distinguish.
Then printed my reference BW picture with the linearised profile an the picture is definitely too dark. Before linearisation it was more-less ok.
I cannot find the reason. Tried to scan to grayscale instead to RGB - the same result. Then realised that my reference picture I use has 20% dot gain profile embeded. So changed both: 21 step wedge and my reference to have the same (e.g. Gamma 2.2) profile - the same result - after linearisation, picture is to dark.
So, my kind questions are as follows:
1) What grayscale profile of printed picture I shoud use for QTR embeded profiles e.g. PK raw neut to have proper result (~= to what I see on my monitor - Eizo Color Edge line, regularly calibrated)? I cannot find it in QTR documentation (gamma 1.8, 2.2? why 21 step wedge has 15% dot gain profile?).
2) Do I do any mistakes in abovementioned linearisation?
3) I assume 21 step wedge tiff should have the same profile when printed as printed picture?
4) Is it possible that Q13 target I have is of bad quality?
5) Any mistakes in PS when using the script?
I tried above on 3 papers, also with baryt profile from QTR - the same result.
ANY halp appreciated. Thanks in advance.