I do not think that the discussion is about which printer delivers best output etc but nevertheless:
With a variety of 4 and 6 picoliter droplets the Z3100 will not make an optical resolution as high as the Epson 3800 which can rely on 3.5 picoliter droplets for best quality. There is a rough rule to compare: 3.5 : 5 picoliter = 0.7 0.7 x 360 = 252 close enough to your 240. The HP will not ask for 360 PPI input but for 300 PPI which makes it all quite logical. Given good + enough data and maximum paper coating quality the higher input qualities of 600 or 720 PPI are available for resp the HP and Epson so the HP print quality is not limited to the 240 PPI you quote for 300 PPI input. A similar approach for a Canon iPF model, 4 picoliter throughout (in all dpi resolutions), this time not for input resolution but for for dot resolution: 3.5 : 4 = 0.875 0.875 x 1440 dpi = 1260, close enough to the 1200 dpi of the Canon. 0.875 x 2880 dpi = 2520, close enough to the 2400 dpi of the Canon. Whether the droplet size and/or dot placement are defined exactly by the numbers published is another question. A rough rule it is, the HP B9180 has to work with the same 4-6 droplet heads the Z3100 has but its dithering/weaving algorithms are better (and will take more processing time per square foot), so lays down a better print quality despite the same droplet sizes. With the exception of the B9180 all manufacturers use smaller droplet sizes, 2- 1 picoliter, for photo quality A3 and A4 printers as the expected viewing distance for print sizes like that will be less.
Hmmm... thanks Ernst for the information, you have given me something to think about (I've read it through three times and almost understood it).
I did not intend to comment on which printer produces best output, however I can see why you took my comment that way.
My intention was to comment on the marked difference in print quality produced when using the same ppi value on different printers. E.g. from the same source file and using my personal standard of print quality, I can produce a larger print using the HP, than I can with the Epson. I.e. when I am printing a BW image with fine diagonal lines, I have to up the source size and send it to the Epson at 360dpi to avoid jaggies which are not present in the HP's output at 240ppi. I am not commenting on the highest print quality that can actually be achieved by either printer.
Up until now I had thought that the HP (along with the driver etc.) merely had a better interpolation algorithm than the Epson.
Am I reading you right in saying that this is actually a result of the Epson having an overall higher resolution?
Thanks,
Richard.