RE: Epson R2400 inks density
Alberto, Thanks for posting this. I don't use a 2400 but I still find the results of the analysis interesting. I assume the values labeled on the vertical axis A represent the UV log density of the ink plus base density of the Pictorico substrate. How were the patches measured? That is what instrument was used? I should fire up my UV densitometer and do the same with my printers. Since you have plots extending across a broad spectrum in the 300 to 900 nm range I assume it's not likely you used a UV densitometer like the xRite 361T which is what I have. I know Mark Nelson has graphs of UV ink density published in his PDN eBook and Clay Harman has recently contributed some measurements with a couple of Epson printers, but I don't think those measure the same spectral width you have. I also noted the 370 nm axis and I assume this is considered the mid-point for the range of UV frequencies that alt processes tend to be most sensitive to. Great work, Don Bryant -----Original Message----- From: Alberto Novo [mailto:alt.list@albertonovo.it] Sent: Wednesday, April 29, 2009 4:52 PM To: Alt-Photo Mailing List Subject: Epson R2400 inks density A week ago I gave to a friend of mine a print of YMCK and RGB patches (Epson R2400 on Pictorico) for an analysis of their UV-VIS spectra, and now I have the results. The graphs are posted in www.albertonovo.it/scan/epson_inks.html What can be seen is that in the 320-400 nm region (UVA), the yellow ink absorbance abruptly falls from about 3.6 at 400 nm to its minimum at about 440 nm (A=1.5). The other inks have a neatly different behaviour, with an absorbance rising when going from 400 to 320 nm. The most dramatic change happens with magenta and cyan, which have an absorbance of about 0.75 @ 400 nm and respectively 3.2 and 3 @ 420 nm. The absorbance values of red, green and blue are not simply the sum of the primary (CMY) colors at a given wavelength, but can be roughly approximated if the sum is multiplied by 2/3 (see for example the curves of C, B and G, the last two being C+M and C+Y, in the 600-750 nm region). Moreover, the absorption of 50% saturated color patches (i.e. R=255, G=255, B=128 for a 50% Y), that one likely thinks they should have 50% absorption of the full strength ones, are three or four times lower (not shown in the graphs). Alberto
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