So "print resolution" is meaningless apparently

[andrew_barrette]

Hi all.

I am trying to print very small features. No problem I figured, since lots of printers claim very good resolutions. So I bought an Epson ET-2800 because it's print resolution was spec'd at 5760DPI. I thought that this meant that the printer could print features at that scale. How naive I was. Apparently 5760DPI (4.4um pixel spacing) refers to nothing more than the motor step-size. Otherwise, not only is the drop positioning not as precise as the spec would suggest (perhaps due to vibration, but I can't figure out how to print at arbitrarily slow speed), but also the drop sizes are much larger than the pixel size.

I made a test pattern consisting of alternating bands with band sizes of 1, 2, 4, 8, 16, 32, and 64 pixels, and printed it on glossy photo paper at 5760 DPI. The band edges are cleaner for horizontal orientation, and are impossible to see by the band size is down to around 8px. So based on that I would say that the printer is performing at 10x it's spec'd resolution. How is this legal?

I see that some printer specs will show the minimum droplet size in picoliters, and I could calculate the drop diameter from this, but come on! Most printer specsheets don't even show this, and I still wouldn't know how large the drop becomes when it splatters. In my test it looks like the droplets are ~8px across or 35.2um, consistent with the true print resolution being 720 DPI.

View attachment 14982

Anyway, I feel like I'm in the dark now. How do I know a printer's true minimum feature size based on it's spec sheet? Are there certain keywords or printer styles that I should be looking out for? Is there someone who does print resolution comparisons for various printer models? Should I be talking to a sales person at the printer company at this point? I am just a hobbyist so wasn't sure what I would find in the consumer printers market.

 

[andrew_barrette]

 

[Ink stained Fingers]

You are victim of some misleading advertising, have a look how printing technically works - an image is divided into pixels which the print mechanism can handle - this is typically in a 720 dpi raster for Epson printers, newer ones at 600dpi, and 600dpi as well for Canon printers, these are max values and depend on the driver/quality settings. Every of these pixels has a color - a RGB value - and these colors are dithered with small ink droplets, the placement of these droplets can be in a raster of 2880 dpi or 5760 dpi - or Canon even at 9600 dpi for some printers, but you cannot control these droplets individually, it is the driver to do the rasterization to approximate the needed color. And you are right that there is an effect of ink spread/dot gain that droplets can bleed into each other but that's not a problem since the droplets should merge together visually anyway for the intended color, and the paper coating has an effect on the amount of the ink spread as well.

You may have a look here showing some more test images

https://www.printerknowledge.com/threads/printer-resolution-tests-epson-and-brother.13640/

You can find more similar postings in the forum.

What do you get as a user as the maximum eff. resolution on image pixel level - it's about 300-350 dpi for Epson printers and slightly less for Canon printers - it depends a little bit on the droplet size and the related dot gain from larger droplets.
So 'print resolution' is not meaningless technically but does not tell you anything about the actual print resolution you can acheive - you cannot print microfilm like resolution with an inkjet printer

 

[Tony4597]

^^This

I think there is a lot of misunderstanding about printer resolution and image resolution and how it affects final quality of an image

Printers typically use two resolutions, one being the print resolution quoted as dots/droplets per inch (DPI) e.g. 4,800 x 2,400 DPI. These figures equate to the number of discrete droplets of ink that can be ‘squirted’ onto the paper in the vertical and horizontal planes. This is a measure of volume normally quoted as picolitres a picolitre is one trillionth of a litre – so small the human eye can't see it. Printers can vary the droplet size over the length and width of the print head travel

The other resolution and perhaps the most important is what the driver reports to the OS as the printer requirements. This is NOT a measure of DPI but is given as PPI (Pixels Per Inch). This is the important measure of how much a print can resolve - assuming of course that the detail is within the image file. It is often (falsely) quoted that the unaided human eye (20/20 vision) cannot resolve more than 300 ppi. While there is some truth in this (the eye perceives 300 ppi as a continuous tone i.e. it does not recognise the space between), the fact is the eye can discern detail at levels of much more. Some claim over 1000ppi.

PPI is what your editing software understands and uses when sending to the printer driver. The print driver expects a resolution equal to the print head nozzles per inch or multiples. So your print head may have 150 or 300 (Canon) nozzles per inch (a guess!) and therefore optimal printing will be had when image dimensions for your required print size match 300, 600 or even 1200 PPI assuming the print driver allows the higher values. Epson printers are usually 360, 720 or 1440 PPI.

The print driver will build/spool bitmap data to send to the printer based on its desired resolution as reported to the OS. Therefore it is always good practice to send the printer data at it’s declared resolution by sizing correctly in your editing application as it will use superior algorithms to those of the print driver in most cases.

 

[Ink stained Fingers]

Epson printers are usually 360, 720 or 1440 PPI.

Which Epson printers run with a native resolution of 1440 dpi ?

 

[Tony4597]

Which Epson printers run with a native resolution of 1440 dpi ?

The native resolution would really depend on the number of nozzles in the print head. Epson pro printers I believe traditionally would have 360 nozzles per inch, Canon 300. AFAIK none would have 1440 nozzles per inch.

I currently use an Epson SC P800 which is a prosumer model. The 1" Epson MicroPiezo AMC print head has 180 nozzles per channel and offers a maximum resolution of 2880 x 1440. Varying droplets as small as 3.5 picoliters.

AFAIK the output resolution declared to the OS for Epson is 360ppi and 720ppi. So in theory the maximum resolution would be 720ppi, however, there is the option of using 'Overdrive' at 2x maximum reported resolution 1440 PPI

 

[andrew_barrette]

Thank you for the replies and the information! Even people printing nice photographs only use 300-600 DPI, but I am trying to make a lenticular prints that would benefit from resolutions far beyond what the human eye can see, so that's why I'm looking for a superprinter.

I had come across that other thread with the DPI tests. I'm glad people are doing that. I wish every printer showed a sample like this to show performance at high resolutions. But again, nobody cares but me.

 

[Tony4597]

....Even people printing nice photographs only use 300-600 DPI,

I still think there is some confusion here or at least the statement can lead others to the wrong conclusion. DPI is a measure of printer resolution and is not related to the image resolution which is in PPI.
The figures quoted above looks like you really are referring to the image resolution which is what your editing software works in and what your printer is expecting so that it can spool to a bitmap image prior to sending the data to the print head. On the other hand your figure could refer to a DPI resolution for plain paper printing.
Only Canon users are likely to print at either 300 or 600 PPI image resolution for optimal print quality and then select the DPI resolution that dictates how the printer squirts ink droplets onto paper. I print at either 360 ot 720 PPI and select either quality or high quality as the source demands which in turn sets the printers DPI to the required amount

but I am trying to make a lenticular prints that would benefit from resolutions far beyond what the human eye can see, so that's why I'm looking for a superprinter.

I have not been involved in lenticular printing, however it is my understanding that there is very little benefit in presenting image data above 150 -300 ppi which is well within the maximum resolution of the human eye. For the printing you may want to use the highest quality available through the driver which may be well over 1000 DPI.

Could you please quote your source of information about the benefit of resolution beyond what our eyes can see?

 

[Ink stained Fingers]

The native resolution would really depend on the number of nozzles in the print head.

No, not at all - the number of nozzles directly impact the printing speed - more nozzles can put more ink onto the paper in a given time. It is a matter of the mechanical construction how the nozzles - the ink ejectors - are arranged - you even can have split nozzle rows for the same color - the 2nd row fits into the gaps of the first row.

there is the option of using 'Overdrive' at 2x maximum reported resolution 1440 PPI

This P800 seems to be about the only one with this option - it is a software trick to overcome limitations of the performance of the resizing routine in the driver which creates rather weak/soft output - for reasons of printing speed on lower performance computers. Qimage offers something similar - you upscale your image to 1440 dpi, send it to the printer and the resizing routine downscales it to 720dpi, there is in some cases some small gain in sharpness since the software gets along better (a little bit) with downscaling than with upscaling. And all this depends very much of your image content in the first place, but I don't think it makes sense for most printing jobs.

 

[andrew_barrette]

I still think there is some confusion here or at least the statement can lead others to the wrong conclusion. DPI is a measure of printer resolution and is not related to the image resolution which is in PPI.
The figures quoted above looks like you really are referring to the image resolution which is what your editing software works in and what your printer is expecting so that it can spool to a bitmap image prior to sending the data to the print head. On the other hand your figure could refer to a DPI resolution for plain paper printing.
Only Canon users are likely to print at either 300 or 600 PPI image resolution for optimal print quality and then select the DPI resolution that dictates how the printer squirts ink droplets onto paper. I print at either 360 ot 720 PPI and select either quality or high quality as the source demands which in turn sets the printers DPI to the required amount

I have not been involved in lenticular printing, however it is my understanding that there is very little benefit in presenting image data above 150 -300 ppi which is well within the maximum resolution of the human eye. For the printing you may want to use the highest quality available through the driver which may be well over 1000 DPI.

Could you please quote your source of information about the benefit of resolution beyond what our eyes can see?

Sounds like I would want to know the PPI limit of a printer rather than the DPI, however printer manufacturers don't spec this and instead spec DPI, but based on your description I'm not sure why the DPI would ever be quoted in the first place. It doesn't matter if you can place 10 dots within one pixel if their position is basically random. It doesn't correlate with "resolution" which is how it is described in the spec.

The lenticular lens sheet has 50 lines per inch. Each line is a pixel, but it will be divided between 10 different images corresponding to 3D angles. So I need at least 500PPI assuming the pixels drawn are perfect, but since they are not I need even higher resolution to ensure that that the 3D transitions look smooth.