image resolution before printing

Json · Oct 22, 2017

Hi all, I was hoping someone could help me clear up my confusion with image resolution and resampling before printing.

I always have my printer setting on the highest dpi, so what should I be aiming for with my image file’s ppi? my usual method has been to keep it as high as possible without up-sampling but I’ve just read somewhere that on Epson printers it is best to have a resolution in multiples of 360. Up to now I’ve been printing with all kinds of resolution numbers so that my image dimensions are not changed much (thinking that would affect the image quality).

So let’s say I have an 6016x4000 pixel image at 720ppi and I wanted to print it 13 inches on the long side. I understand I don’t have enough pixels to send that file to the printer at 720ppi, so I can:

Upsample it to 9360x6223 pixels keeping the file at 720ppi
Downsample it to 4680x3112 pixels at 360ppi
Or I can change the image resolution to 462ppi which would not change the pixel dimensions much at all.

Is there any advantage in any of those 3 options?

If I get some free time this week I might try this out and see if I can see any difference but I’m sure people have some real experience with this already

wiltw · Oct 23, 2017

PIXELS per inch (ppi) has NOTHING to do with DOTS per inch (dpi) . If you print a 3000x2000 pixel image to fill a 30" x20" print, you end up with 100 PIXELS per inch on the print. Period.

If you print that 3000x2000 pixel image on an Epson XP-640 printer, whether you print 6"x4" print or a 10"x8" print, both print sizes would use 5760 x 1440 dpi (DOTS per inch) of INK
The smaller print would have 500 Pixels per inch, while the larger print would have 250 Pixels per inch, both at 5760 x 1440 dpi (DOTS per inch) of INK

The Pixel per inch is merely a DERIVED number
[# of pixel in original image] / [number of inches of print] = ppi

The Dots per inch of ink are entirely dependent upon the printer which makes the print, and is NOT at all related to the size of the print...the dpi is fixed, regardless of print inches.

Epson XP-640 has up to 5760 x 1440 dpi (DOTS per inch) of INK
Canon iP8720 has up to 9600 x 2400 dpi (DOTS per inch) of INK

even when both printers make the same 250 Pixel per inch (8" wide) print

RalphLambrecht · Oct 23, 2017

wiltw said:
PIXELS per inch (ppi) has NOTHING to do with DOTS per inch (dpi) . If you print a 3000x2000 pixel image to fill a 30" x20" print, you end up with 100 PIXELS per inch on the print. Period.

If you print that 3000x2000 pixel image on an Epson XP-640 printer, whether you print 6"x4" print or a 10"x8" print, both print sizes would use 5760 x 1440 dpi (DOTS per inch) of INK
The smaller print would have 500 Pixels per inch, while the larger print would have 250 Pixels per inch, both at 5760 x 1440 dpi (DOTS per inch) of INK

The Pixel per inch is merely a DERIVED number
[# of pixel in original image] / [number of inches of print] = ppi

The Dots per inch of ink are entirely dependent upon the printer which makes the print, and is NOT at all related to the size of the print...the dpi is fixed, regardless of print inches.

Epson XP-640 has up to 5760 x 1440 dpi (DOTS per inch) of INK

Canon iP8720 has up to 9600 x 2400 dpi (DOTS per inch) of INK

even when both printers make the same 250 Pixel per inch (8" wide) print

I've printed at all kinds of resolutions to my Epson 3880 and cannot make out any significant differences. They all look good but my default is 300dpi.

wiltw · Oct 23, 2017

RalphLambrecht said:
I've printed at all kinds of resolutions to my Epson 3880 and cannot make out any significant differences. They all look good but my default is 300dpi.

Other learning points...

'300dpi'...Is that the EXIF value in the JPG file? That means SQUAT for any purpose other than to define the 'screen' density which dictates the photo quality when printed on an OFFSET PRINTER. National Geographic uses a high dpi, the local newspaper uses a low dpi for printing the identical photo, and you can certainly see the difference.
It is indeed possible to control ink density on an inkjet printer, via the 'Quality' parameter...a draft quality image does not look as good as a 'High' quality image from the same printer, even assuming the identical image (pixels per inch)...the dpi parameter is changed between different Quality parameter.

Json · Oct 23, 2017

Thanks for the responses so far. I do understand the difference between ppi and dpi. I am not talking about printing dpi in this case - like I said I leave my printer quality setting on it's highest.

I think the main crux of my question is more to do with resizing the image before printing. You have to make a decision about print size and when you do that in photoshop there is a decision to be made for resolution too. Are you saying that field has no effect at all on printing?

My thought was the image ppi (the resolution field when resizing) is translated to dpi during printing - so the higher the better. Thats why I'm asking about the best strategy re. resizing in my original post (upsampling, downsampling, etc)

markbarendt · Oct 23, 2017

The printer's dots have a very specific size and spacing. Given that, the printer's specific capability is what I target.

If the printer naturally does 300dpi then 300*12 = 3600 on that side for a 12" print.

If you use a different dpi than the printer's natural dpi the printer's software has to redo (upsize/downsize) the image to fit. Your 720*12 photo gets resized, in the printer to 300*12.

RalphLambrecht · Oct 23, 2017

markbarendt said:
The printer's dots have a very specific size and spacing. Given that, the printer's specific capability is what I target.

If the printer naturally does 300dpi then 300*12 = 3600 on that side for a 12" print.

If you use a different dpi than the printer's natural dpi the printer's software has to redo (upsize/downsize) the image to fit. Your 720*12 photo gets resized, in the printer to 300*12.

It's interesting to me that such an important topic is so poorly documented.

Json · Oct 23, 2017

markbarendt said:
The printer's dots have a very specific size and spacing. Given that, the printer's specific capability is what I target.

If the printer naturally does 300dpi then 300*12 = 3600 on that side for a 12" print.

If you use a different dpi than the printer's natural dpi the printer's software has to redo (upsize/downsize) the image to fit. Your 720*12 photo gets resized, in the printer to 300*12.

Ah now that is new info for me, thanks for that Mark.

What is a printers “natural” dpi though? Are you saying it is always 300dpi? My Epson 4800 has a number of different quality settings and all I know for sure from the user guide is that it’s max resolution is 2880 x 1440 dpi.

Also in your example, say you resize the image to 3600px for a 12” print in photoshop, what would you set the resolution to be as an ideal?

nmp · Oct 23, 2017

This article, perhaps dated given there have been new iterations of printers lately, talks about the topic.

https://www.digitalphotopro.com/technique/photography-workflow/the-right-resolution/

wiltw · Oct 23, 2017

markbarendt said:
The printer's dots have a very specific size and spacing. Given that, the printer's specific capability is what I target.

If the printer naturally does 300dpi then 300*12 = 3600 on that side for a 12" print.

If you use a different dpi than the printer's natural dpi the printer's software has to redo (upsize/downsize) the image to fit. Your 720*12 photo gets resized, in the printer to 300*12.

And there we have a misuse of terms, leading to more confusion!

Printers are often said to do 300dpi, but actually the dpi spec is 'up to 9600 dpi' (in the case of Canon iP8720 that I mentioned earlier!)
But if there is a desire to have 300 PIXELS per inch on the final print, you need an input file which is 3600 PIXELS in the 12" direction.

The 9600 dpi is the 'dpi' for the Canon iP8720; Epson XP-640 has up to 5760 x 1440 dpi . So just what is 'natural dpi'???

Epson themselves publish:
"Can I select a print resolution by indicating a specific DPI (dots per inch) setting?

No, the print resolution is determined by other driver settings."

There is further cause for confusion by many claims of the past.

It has been said that Epson pro printers’ print heads have a reported output resolution of 360/720 dpi, depending on the print mode, and Canon and other printers have a reported 300/600 dpi. What is meant by by “reported”? The print driver communicates with the operating system print pipeline and states its resolution in dots per inch. You can send any output resolution to the print head, but the print pipeline will resample the input resolution and send the printer the resolution it asks for. Yet the actual printers claim numbers like 4800 and 9600ppi while print driver communicates with the operating system print pipeline and states its resolution in 300 or 360 dots per inch?!?!? One cannot get a straight answer from the app, from the O/S, or the printer hardware guys, and testing by folks yields inconclusive and confused results!

Json · Oct 23, 2017

Thanks Niranjan, I'll give that a read and hopefully it will clear things up - it looks like exactly what I need.

wiltw, what would your recommendation be for resizing and choosing a resolution (ppi) for an image to be printed 12" wide on a printer that has a maximum dpi of 2880x1440 when the original image is 6016x4000 pixels (for the image to look good at close range - say 8-10")?

(that might be the most specific question I've ever asked anyone )

Prof_Pixel · Oct 23, 2017

wiltw said:
PIXELS per inch (ppi) has NOTHING to do with DOTS per inch (dpi) . If you print a 3000x2000 pixel image to fill a 30" x20" print, you end up with 100 PIXELS per inch on the print. Period.

If you print that 3000x2000 pixel image on an Epson XP-640 printer, whether you print 6"x4" print or a 10"x8" print, both print sizes would use 5760 x 1440 dpi (DOTS per inch) of INK
The smaller print would have 500 Pixels per inch, while the larger print would have 250 Pixels per inch, both at 5760 x 1440 dpi (DOTS per inch) of INK

The Pixel per inch is merely a DERIVED number
[# of pixel in original image] / [number of inches of print] = ppi

Well said. I've been fighting the dots are not pixels and it's the total number of pixels that count battle going back about 25 years when I made many presentations on digital imaging for Kodak. Too many people still don't understand.

markbarendt · Oct 23, 2017

Json said:
Ah now that is new info for me, thanks for that Mark.

What is a printers “natural” dpi though? Are you saying it is always 300dpi? My Epson 4800 has a number of different quality settings and all I know for sure from the user guide is that it’s max resolution is 2880 x 1440 dpi.

Also in your example, say you resize the image to 3600px for a 12” print in photoshop, what would you set the resolution to be as an ideal?

Every printer is different, and no, it’s not always 300 dpi.
I freely admit that most of this is over my head as far as the science but there are a few rules-of-thumb that help, that also make good general sense.

First, the software the printer uses to do the conversion is really good in most cases.

Second is that for photographic quality, for what the human eye can resolve at a normal photographic viewing distances, 300 ppi works really good. That number has been used for years by pro labs and is well proven.

Higher ppi’s help where the original will be magnified. So from a 135 film/a full frame sensor the data is based on a real space of about 1”x1.5” and the dpi/ppi it catches needs to be stretched out to cover say an 8”x12” paper. So at 300 dpi you need a camera that does about 2400dpi/ppi. 2400X3600=8,640,000 so you need an 8 mega pixel camera, yep really that’s all you need at 300 ppi. At 240 which a lot of photographers have used very successfully a 6mp camera is plenty mathematically. For professional printing to canvas the norm is close to 100 ppi, an 8mp camera can get you to a 24” x 36” print.

Also notice that 2880x1440 isn’t a ‘square’ measurement geometrically. It’s a bit like using centimeters for horizontal and inches for vertical to define a square. The printer does the maths though so don’t sweat that too much.

Third, and this is where the magic is, you need to see the final result at the appropriate size to determine proper sharpening and tonality. This is where it gets tough because screen resolution dpi doesn’t match paper print resolution dpi normally. On screen in order to see what’s really happening the image needs to be out 100% magnification, no larger no smaller, otherwise the pixel count won’t match the real dots on the screen and that means the computer has to fudge (guess a bit) to make the image on the screen. 100% is the only place that you can come close to saying what the paper is going to look like.

The fourth thing to remember is that the math defines the ideal but the ideal is rarely needed to do really great work and it’s the final use specs that should be your target, not the theoretical most and biggest.

Prof_Pixel · Oct 23, 2017

markbarendt said:
Second is that for photographic quality, for what the human eye can resolve at a normal photographic viewing distances, 300 dpi works really good. That number has been used for years by pro labs and is well proven.

Please use 300 PIXELS/inch and not dpi. 300 PPI makes a good looking print, but I had a laser printer years ago that was 300 DPI, and it was definitely NOT photo quality. I try to use DOTS per inch (dpi) only when talking about actual DOTs and only PIXELs per inch (ppi) when talking about pixels.

markbarendt · Oct 23, 2017

Ok, fixed.

nmp · Oct 23, 2017

I can see Prof_Pixel getting mad at that imposter Prof_Dot...

wiltw · Oct 23, 2017

Prof_Pixel said:
Well said. I've been fighting the dots are not pixels and it's the total number of pixels that count battle going back about 25 years when I made many presentations on digital imaging for Kodak. Too many people still don't understand.

It certain does not help that the INDUSTRY adds to the confusion rather than clear it up! Canon puts in its EXIF the term 'dpi' and sets it to an arbitrary '72' while another manufacturer might embed '300' for the same parameter, and yet both values mean nothing other than to an offset press operator. And lots of folks THINK that if they edit and change this value, it would affect the print quality from their inkjets...NOT!
Companies like Adobe mix up 'dpi' and 'ppi' in the user interface and you find references to 'dpi' when they clear should be talking about PIXELS, the pickheads mix up P and D.

wiltw · Oct 23, 2017

markbarendt said:
This is where it gets tough because screen resolution dpi doesn’t match paper print resolution dpi normally. On screen in order to see what’s really happening the image needs to be out 100% magnification, no larger no smaller, otherwise the pixel count won’t match the real dots on the screen and that means the computer has to fudge (guess a bit) to make the image on the screen. 100% is the only place that you can come close to saying what the paper is going to look like.

NO, that (blue text) is not correct. If I view an image at 100% on my monitor, my 2560 x 1440 27" monitor spreads 2560 pixels across 23.5" horizontal, so my 5472 pixel horizontal images from my 7DII would be spread across a 50" wide print when I view an image 'at 100%' on my monitor!!! ONLY if I want to make a 50" print and view it from about 2' away would my view on the monitor reflect reality.

Prof_Pixel · Oct 23, 2017

wiltw said:
It certain does not help that the INDUSTRY adds to the confusion rather than clear it up! ...
Companies like Adobe mix up 'dpi' and 'ppi' in the user interface and you find references to 'dpi' when they clear should be talking about PIXELS, the pickheads mix up P and D.

The confusion goes back to the earliest days of digital imaging. I suspect the problem is that many of the early researchers and developers came out of the graphics art industry where dots ARE used.

jim10219 · Oct 23, 2017

A printer’s max effective DPI is usually around 300. Some are less, some are more. But you’ll often see printers advertised with numbers quite higher than that. They get those numbers by multiplying the max effective DPI by the number of ink cartridges, since each ink cartridge can put a dot there, one on top of another. So, the more ink cartridges your printer has, the higher the advertised DPI. This doesn’t mean it prints at a higher resolution though. Just that it can lay down more dots per inch by overlapping them. So raw DPI numbers aren’t a good way of determining a printer’s resolution. However, if you understand them, they can still be helpful.

The advantage to printing with a resolution the same as your printer’s natural resolution is you can let software like Photoshop manage the pixel to dot conversion instead of relying on your printer’s driver. It’s really more theory than good practice though. In reality, it usually won’t make a noticeable difference either way. However, you should always let a graphic editing program like Photoshop scale the photo, and not rely on your printers drivers to do this, unless you are using a RIP software to control your printer.

markbarendt · Oct 24, 2017

wiltw said:
NO, that (blue text) is not correct. If I view an image at 100% on my monitor, my 2560 x 1440 27" monitor spreads 2560 pixels across 23.5" horizontal, so my 5472 pixel horizontal images from my 7DII would be spread across a 50" wide print when I view an image 'at 100%' on my monitor!!! ONLY if I want to make a 50" print and view it from about 2' away would my view on the monitor reflect reality.

Newer monitors with higher dpi’s fix that problem, well they get closer to fixing it.

It’s problematic definitely, but 100% is the only place where there is a 1 pixel to 1 dot relationship, all other magnifications require interpolation so things like sharpening are skewed.

With experience those skewed looks can be good enough but they are typically not a match to paper size.

markbarendt · Oct 24, 2017

wiltw said:
NO, that (blue text) is not correct. If I view an image at 100% on my monitor, my 2560 x 1440 27" monitor spreads 2560 pixels across 23.5" horizontal, so my 5472 pixel horizontal images from my 7DII would be spread across a 50" wide print when I view an image 'at 100%' on my monitor!!! ONLY if I want to make a 50" print and view it from about 2' away would my view on the monitor reflect reality.

Had another thought re this post.

5472/300=18.24

Unless you are printing 18.24 inches on that 5472 pixel side the printer will interpolate when it downsizes/upsizes to fit the paper, again messing with the sharpening.

image resolution before printing

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