I posted this query on the QTR site, but received no responses. Can someone here advise me?
I have for many years been printing with Quadtone RIP on my Epson 1440 at a (maximum?) dpi of 2880. I have just recently purchased from Epson a 1430 as a back-up printer. When printing initial test photos on the 1430 I noticed what is perhaps termed "laddering" (narrow lines) on about 10% of the edges (top and bottom in Portrait mode, left and right in Landscape mode) in the direction the print head moves. Thinking this was perhaps a problem with the new printer, I went over some reasonably extensive testing with an Epson tech rep on the phone and determined that the printer was working fine. He opined the problem might be with my printing software. I then ran another test print with QTR, but changed the dpi to 1440 -- and the print turned out fine. I do not understand (yet) all the relevant terminology, so I'd be most appreciative if someone would explain to me (1) the difference in meaning between the two dpi settings, (2) the possible reason for this difference between the two printers' outputs, and (3) what possible loss in quality I might experience by needing to use the 1440 dpi setting with the 1430 printer. Many thanks.
Hi Jim,
These 1440 / 2880 DPI (
dots per inch) settings are related to the dithering process that is used to create intermediate colors from only a limited number of ink colors. One would expect that the 2880 DPI setting uses a finer pattern with droplet placement at the highest physical/mechanical positioning possible for the printer.
Maybe there was another issue complicating the analysis of your issue, namely the actual
pixel resolution that the printer driver uses. The Epson printers are capable of using 2 distinct pixel resolutions (PPI =
pixels per inch). The higher (720 PPI) resolution is usually disabled, until the 'Finest detail' selection is activated in the printer driver options. When it is disabled, any input to the printer driver will be resampled to 360 PPI, and the resampling method is a relatively low quality one, which may lead to visible resampling artifacts if the subject matter (and the viewer) is critical enough.
Each uniform color pixel (at 1/720th inch position accuracy) will be subdivided in even smaller mechanical placement positions to place dithered droplets for simulated intermediate ink colors.
Then there is also a possibility that print head alignment for your output media was not optimal.
These three printer-side issues may or may not amplify each other. Of course, there is also the issue of image resolution as it is sent to the printer. It's best to resample to 720 PPI with a good software resampling algorithm, output sharpen after that, and then send that (with color managed tones) to the printer driver (which can skip resampling, and only needs to dither and drive the head and paper transport mechanism).
One would expect that if the image data is properly tailor-made at 720 PPI first, that the 2880 DPI dithering setting would provide the best quality (most detailed/smooth dithering of color). But since you experienced otherwise, there may be something else throwing a spanner in the works. Do check you driver's 'Finest detail' option, and make sure it is active.
If you want to test resolution and head alignment issues, you can use my
Printer resolution test target. Don't worry is you cannot make a perfect print of that target though, it's hyper critical, but it might reveal other (mechanical) mis-alignment/resolution issues that should be addressed first.
Cheers,
Bart
