Correct Print Resolution for Epson Printers

[steverap]

Thanks, Andrew, I was hoping for succinct answers to my two questions and I now have them - thanks!

[JRSmit]

Jeff Schewe and others suggest sending files to an Epson printer with print resolutions of 360 or 720 ppi, so if a file's resolution is greater than 360 but less than 720, it should be upsampled in, say, Lightroom's Print Job module by checking Print Resolution and entering 720. Does that remain the consensus advice about printing from Lightroom?

The objective is to send the file to the print pipeline with the pixels per inch as the print pipeline expects. So if in W10 the printer driver of say An sc-p9000 is set to print quality level 5 (2880dpi) and Fine Details is set to On, the expected ppi is 720. If not the print pipeline Will rerezz to 720, and then do the printing.

If you set the driver to say pql is 4 and FD is off, then 360ppi.

Note the W10 pipeline needs the FD set to On to process the file as 720ppi. If not set it will process at 360ppi, but the printer itself(print engine) will process at 2880dpi.

So when using Lightroom, you can set your print templates to the required print resolution, and Lightroom will rerezz to the set PPI.
Very efficiënt.

[Rand47]

And, I think it is important for the OP to know that not all Epson printers are 360/720.  Some of the newer ones, e.g. the SC P7570 / 9570 are 2400 x 1200 heads.  So, the appropriate LR res settings would be 300 / 600 as with Canon.

Rand

[Bart_van_der_Wolf]

And, I think it is important for the OP to know that not all Epson printers are 360/720.  Some of the newer ones, e.g. the SC P7570 / 9570 are 2400 x 1200 heads.  So, the appropriate LR res settings would be 300 / 600 as with Canon.

Correct, and an application like Qimage will sort out the optimal settings by automatically interrogating the printer driver. That will also show that a "Finest Detail" setting is required to allow printing at 720 PPI.

A question that seems to remain unanswered is; what to do if the image size results in a PPI between 360 and 720 (or 300 and 600) PPI?
The answer is, why waste real image data by downsampling? Use the next higher resolution instead, i.e. 720 (or 600) PPI, and avoid downsampling artifacts (even if they will be hard to spot in the final print). There could be a reason to downsample to 360 (or 300) PPI, and that is when the total number of pixels exceeds the maximum allowable width of the paper (roll) in pixels.

In theory, there can also be a memory buffer limit to how many pixels can be sent to the printer driver with large format output, but an application like Qimage can usually avoid that by sending chunks of data to the printer.

Qimage (Ultimate, not sure about the Qimage One versions) also support an "Overdrive" printing mode, that's useful when printing large files on smaller output formats. When the resulting PPI for a given output size would exceed the maximum printer resolution of 720 (or 600 PPI), Qimage will attempt to print at something like 1440 (or 1200) PPI, thus improving the print quality even further.

[digitaldog]

Qimage (Ultimate, not sure about the Qimage One versions) also support an "Overdrive" printing mode, that's useful when printing large files on smaller output formats.

Yes, my copy (on Mac) has this option.

[Bart_van_der_Wolf]

Yes, my copy (on Mac) has this option.

Good to know. The effect may be subtle, but it does work for the better.

[JRSmit]

In an earlier thread I showed the effect if you send a file to the printer in a ppi resolution not equal to the setting of the driver. In short a poor result. Do not know how to copy the I’d of that thread.

[texshooter]

Since the Epson printer has a maximum print resolution  of 2880 dpi, why is the maximum  image resolution limited to 720 ppi? If I'm working with a super high resolution image (such as from image stacking), why can't I send a 2880 ppi file to the printer?  If the printer can lay down 2880 dots-per-inch onto the paper, it should in theory be able to manage a 2880 pixels-per-inch image file, no?

[digitaldog]

Since the Epson printer has a maximum print resolution  of 2880 dpi, why is the maximum  image resolution limited to 720 ppi? If I'm working with a super high resolution image (such as from image stacking), why can't I send a 2880 ppi file to the printer?  If the printer can lay down 2880 dots-per-inch onto the paper, it should in theory be able to manage a 2880 pixels-per-inch image file, no?

There is no reason to send 1 image pixel to such a printer at those values and further as mentioned, those values differ from the actual native possible printer resolution (e.g. 360/720).

[Bart_van_der_Wolf]

Since the Epson printer has a maximum print resolution  of 2880 dpi, why is the maximum  image resolution limited to 720 ppi?

Because we need to mix ink color dots for different per pixel-colors and brightnesses (by placing the single color dots adjacent to each other or slightly overlapping) that are in between the individual colors and white background.

So, the individual dots of ink (or absence thereof, thus revealing background-white) are placed with e.g. a 1/2880th inch accuracy, which allows to place at least 4x4=16 of them side-by-side per 1/ 720th x 1/720th inch pixel. By varying the droplet size one can create even finer gradations of intermediate colors, also mixed by ink diffusion. Also, 720 PPI is roughly 2x the limit of human visual acuity at reading distance, so adjacent pixels are optically diffused/blended by our visual system.

Printing at higher pixel resolution than visual acuity requires, helps with blending gradations between pixels, and it helps with achieving "Vernier acuity" .

[texshooter]

I didn't think about the necessity of mixing multiple ink dots to render a single pixel color.  That makes sense.

I was also wondering why the printer head has a higher dot density in the horizontal direction (ie, 2880 dpi) than it does in the vertical direction (ie, 1440 dpi). That seems a bit cockeyed.  Camera image sensors have a uniform pixel density across its two-dimensional surface.  Why not printer heads?

[digitaldog]

I was also wondering why the printer head has a higher dot density in the horizontal direction (ie, 2880 dpi) than it does in the vertical direction (ie, 1440 dpi). That seems a bit cockeyed. 

Ever view the spec's of a flatbed scanner? Optical resolution one dimension, stepper motor the other; perhaps the same here?

[texshooter]

Ever view the spec's of a flatbed scanner?

No.  I'm old but not that old 😁

[Rand47]

Because we need to mix ink color dots for different per pixel-colors and brightnesses (by placing the single color dots adjacent to each other or slightly overlapping) that are in between the individual colors and white background.

So, the individual dots of ink (or absence thereof, thus revealing background-white) are placed with e.g. a 1/2880th inch accuracy, which allows to place at least 4x4=16 of them side-by-side per 1/ 720th x 1/720th inch pixel. By varying the droplet size one can create even finer gradations of intermediate colors, also mixed by ink diffusion. Also, 720 PPI is roughly 2x the limit of human visual acuity at reading distance, so adjacent pixels are optically diffused/blended by our visual system.

Printing at higher pixel resolution than visual acuity requires, helps with blending gradations between pixels, and it helps with achieving "Vernier acuity" .

Bart,

Thanks for this.  Excellent stuff. Helped my overall general understanding a lot!

Rand

[steverap]

Allow me to add my gratitude to the group, this was enormously helpful - thanks!

[BAB]

WoW! the math hasn't changed has it?   
2+2=4 unless you're selling a large bridge.

Any even division of 1440 for Epson is the right print resolution 1440 divided by 8= 180 you can print at 180 and get great results.
As far as 2880 its mostly marketing hype.

But try it out print at 1440 and 2880 if you see a noticeable difference on the wall from 6-8' then you can be sure.

[JRSmit]

WoW! the math hasn't changed has it?   
2+2=4 unless you're selling a large bridge.

Any even division of 1440 for Epson is the right print resolution 1440 divided by 8= 180 you can print at 180 and get great results.
As far as 2880 its mostly marketing hype.

But try it out print at 1440 and 2880 if you see a noticeable difference on the wall from 6-8' then you can be sure.

You missed the point that the printer driver expects the ppi as set in the pal parameter. And if not it will rerezz to set value , but with the neirest neighbor method, rather ugly.
As for 2880 being marketing, may be for you, my experience is that it is of value.

[bjanes]

In terms of LR or otherwise, yes.
Jeff's piece, a must read:
https://www.digitalphotopro.com/technique/photography-workflow/the-right-resolution/

It seems to me that much confusion in this discussion is failure to distinguish between dots and pixels. This difference is explained very well in Color Management, 2nd Ed by Fraser, Murphy, and Bunting (pages 56 and 57). A pixel is an image sample with red, green and blue with each color having different and continuously variable intensities (continuity is limited by digital encoding, commonly 8 or 16 bits). A continuous-tone device such as a monitor or contone printer (e.g dye sublimation) can display these pixels directly, but our injket printers need to break down the pixel into dots using error diffusion halftoning. My Epson 3880 can use a maximum of 2880 x 1440 dpi. This resolution refers to placement of the dots, and with error diffusion halftoning the relationship of the dots to the actual pixels is rather tenuous.

Jeff's article to which you refer is excellent, but he appears to use dpi and ppi interchangeably.

Bill

[digitaldog]

In terms of Jeffs article, one can use PPI and DPI interchangeably: image pixels are used to create dots.
What makes you believe that an ink jet print can't be considered continuous tone? Under a strong enough magnifier, what is? Certainly not a display who's output resolution can be lower than some digital prints.Lastly, even encoding 8 bits, two different numbers can result in the same color.

[jrsforums]

In terms of Jeffs article, one can use PPI and DPI interchangeably: image pixels are used to create dots.
What makes you believe that an ink jet print can't be considered continuous tone? Under a strong enough magnifier, what is? Certainly not a display who's output resolution can be lower than some digital prints.Lastly, even encoding 8 bits, two different numbers can result in the same color.

Interchanging pixels and dots just causes confusion.  ‘Pixels Per Inch’ is a definition of input to the printer.  ‘Dots Per Inch’ is the output of the printer to it’s media.

Jeff, in the article does misuse dpi when he says, “... Epson pro printers’ print heads have a reported output resolution of 360/720 dpi...”. The 360/760 is an expected input resolution (ppi) that the printer expects to get.  If it gets a different number it (either in driver or printer software) will interpolate to the number.

A monitor may appear ‘continuous’ tone, but it is clearly made up of individual bits of colored (usually rgb) lights.  Dye-sub may be considered ‘continuous tone’ due to the overlay blending of colors, but it is, as I understand, usually laid down in a pattern of dots.  That an inkjet printer (or billboard) viewed at a far enough distance appears continuous, does not change the definition that it is created by dots. 

Lastly, I think the statement would be “even encoding 8 bit, two different numbers can be perceived as the same color”