More ink equal lighter black?!?

[picturesfromthelow]

Hi guys,
in the last couple of days I'v been trying to profile Moab Entrada Rag Natural paper for my Epson 3880's ABW mode (please note that I'm on Windows and printing with profile for ABW still works). I'm using Color Munki and following the method devised by Keith Cooper of Northlight Images. I did som experimenting with the print drivers parameters and I found that sometimes I get a lighter black value when increasing total ink density (all other parameters being equal). We are talking of small differences, say from L 17 to L 18,5 when increasing ink density by 5% but still I find this evidence totally counterintuitive. Is that normal? I just would like to understand if I'm doing something wrong. In a similar fashion, I also found that for some media types, lowering ink density does not produce a lighter black, sometimes the result is a darker black! I'm quite confused right now

Cheers,
Luca

[Ernst Dinkla]

First of all, increasing the ink load on black pigment inks does not translate to increased Dmax at some point and a reversal to lower density can happen. The same for chroma with color inks. The black pigment ink not absorbed enough by the paper coating can create a higher light reflection than when more embedded in the coating layer. When you measure partitioning stepwedges as used for the Quadtone Rip it is quite normal to find a lower density on the 100% patch and the Dmax to be at the 95% or 90% patch. So a lower black ink load is then chosen.

On the other hand in most OEM drivers the ink load control suggested in the advanced driver settings usually is a gamma correction that has more impact on the mid tones than on the ends of the tone range. In other words it will not increase black ink lay down at 100% but could influence the lower value patches there. I could be wrong on that for the 3880 driver though or on the ABW mode of it.

What you could do is select another media/paper preset in the driver that could have another real ink limit, higher or lower. It is a black box. Choices are limited. Best thing to do is adopting the Quadtone Rip for B&W printing.

Met vriendelijke groet, Ernst

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2014 update, 700+ inkjet media white spectral plots

[picturesfromthelow]

Ernst, thank you for your detailed reply. Yes, I got the impression that fiddling with the parameters of the Epson's driver did not give me the degree of control I was hoping for. It's just that I am really trying hard not to delve into RIPs . In the end I think that, if using Epson's ABW, I may just stick with the most appropriate media type for my chosen paper without trying to tweak it that much.
By the way, your Spectrum Viz tool has been, and still is, incredibly useful, paired with Aardenburg Imaging information. Thanks for it as well!

Luca