Ernst,
I adjusted the curve in Photoshop until the maximum UV transmission density was about log 2.2, more or less what I wanted. This was with color managment set to Grayscale and printing with only the gray inks. For some reasons this setting caused a lot of banding and a very grainy looking negative. By contrast, printing an RGB file in grayscale with the composite black gives a maximum transmission density of about 2.27, and visually it is very smooth with no banding.
Sandy
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Though I didn't expect banding I thought it would be grainier. In RGB and with composite grey not replaced by grey ink (so not a long black generation) you will get three softer tone droplets LC,LM,Y or CMY covering a wider area than the one hard grey or black droplet that replaces the same tone in greyscale printing. More or less similar to how collotype is smoother printing than an offset halftone plate. If HP would replace the CMY droplets with a grey ink of related density it wouldn't reduce inkload and reducing inkload to some degree has many advantages.
The B9180 has the same inkset the Z2100 has, correct? If you also reduce the tonal range to 2.2 your negative most likely will use one grey ink mainly and hardly the photo black. It could be that the tonal range compressed can't find enough nuances in dot expression of one grey ink and by that is prone to banding = more a clustering of tone steps to the same dot density, another possibility: the one grey ink dot distribution gets so stretched in the stochastic pattern printing that it shows, on thin ice here. Printing on film usually gives very well defined round dots, that adds too.
There's also the droplet size difference of 4 and 6 picoliter per ink hue and grey inks that may play a role here. I do not know how that is on the B9180 but for example the MK,C,M,Y, on the Z2100 are squirted as 6 picoliter droplets, the LC, LM, LG and PK as 4 picoliter droplets. That emphasises the hard core density of a 4 picolitre grey or black droplet on a transparant area of film even more compared to 3 CMY droplets of 6 picoliter size on the same area. Depending on where the partioning between the lighter and darker inks happens you will notice differences in grain variation. Check it with a microscope.
If smoothess is the most important factor then you better skip grey inks on the B9180. I'm not even sure whether a cyan or red bias in color printing then would make better smoothness, could be that an even distribution of LCLMYLG + CMYK droplets is better than taking out LG and K in the mixes. In other words: reducing black generation by coloring the image may not be better.
Ernst Dinkla
try: [a href=\"http://groups.yahoo.com/group/Wide_Inkjet_Printers/]http://groups.yahoo.com/group/Wide_Inkjet_Printers/[/url]