Print size vs resolution

[metallion58]

Dear moderators...
I know this belongs in another section but there are so many questions about this that I think it should be shown to the most people.
There's a great video explaining the link between resolution and maximum printing size and how to optimize that in Lightroom or Photoshop.
Here's the link
There's also a link for an interactive spreadsheet in the comments just under the video that you can download and use on your computer.
Thought I'd share.

[ravncat]

That's pretty useful, and good information.

You can go larger for a few other reasons he doesn't mention that is dependent upon ink, paper and sharpening settings. Some papers bleed more for example, so the dots on paper end up larger when they are absorbed into the paper. Guidelines for that are alot more complex and I don't fully understand them, so the chart provided is a good reference starting point.

It's also worth noting that you should upsample (or even downsample depending on print size) to 360ppi or 720ppi for most epson inkjet printers, instead of 240 or 300, the reasons for this have to do with the way the printer pipeline and datastream works, the number 360 is native to the printer and results are noticeably better (at least to the trained eye)

[OsmosisStudios]

I actually found that to be more confusing than anything. He only really gets into it once he starts playing in PS, but everything before that is just a mess.

Printing isnt as complicated as it seems, but its also a lot more complicated than it seems: he says you can refer to another episode to discover the other elements, but they also have a significant impact on print quality.

This also doesnt address personal differences (can YOU tell what 100DPI is compared to 200DPI?) or different printing systems.

[ravncat]

I missed part of the beginning, the number blocks made some sense, i think in trying to explain the difference between overall dimensions and print resolution.

The visual reference for print viewing distance got the point across but there wasn't really any information about what kind of guidelines you should be looking at for printing distance. I wish he would've explained what "viewing distance" the numbers he stated were really optimized for.

The difference between 100 and 200 ppi is also really dependant upon the print size and the file size and way that it was compressed. I agree with you osmosis, there's alot more depth to the subject, but I think for most people, that chart given will give them a good starting point for a high quality large print.

[metallion58]

It is, of course, incomplete but I thought it was a lot of good info for a 15 minutes video.
And BTW, if you click on plus just under the video, you'll have a link to actually download the Excel interactive table that he use. playing around with that gives you an even better idea of what he talks about.
As for the block thing, it is to show what the software does when you resample which is basically calculating what should be between pixels when you go over your original resolution or throwing away information and smoothing things out when you go under. At least, that's what I understood from his explanations.
Did I get that correctly?

[SwissJon]

So where did he get this magic 135dpi toward the end??

Thanks Ravncat.. So you're saying that the printer has a native resolution, just like a monitor.. I guess that makes sense. I've an Epson, I'll stick to those resolutions.

[SwissJon]

I think one crucial point he missed was the relationship between viewing distance and DPI.

I'm going to have a stab at this, someone correct me if I've got it wrong.

Ok. Let's take a random starting point. I'll hazard a guess that printing between 240 and 300 dpi is designed to be viewed between 1 and 2 feet from your eyes (the distance you hold a magazine). I'm going to say 256 dpi and 2 feet because it makes the maths easier, and that's roughly how far I hold a magazine when reading it. Having said that, let's say your image is 4096 pixels by 2048 pixels giving a print size of 16 inches by 8 inches..a completely random size for easy maths..

Ok, so if you move something twice the distance from your eyes, it appears to be half the vertical and horizontal size. I've no proof of this, it could just be my eyes, but that's what I saw when I moved an object and measured it relative to a distant ruler.

Now we come to the math. If you decide that your 256dpi picture ought to be seen from 4ft not 2 ft, let's say you're going to glue it to the ground.. A bit of pavement art.. You can print it at 128dpi and still get the same "apparent" resolution. But now the print is 32 inches by 16 inches. Double the distance again. 8 feet gives you 64dpi, and a print size of 64inches by 32inches. Keep going.. At 16 feet you have 32dpi, and a print size of 128x64 inches.. Keep this going 32 feet, 16dpi gives 256x128, 64feet, 8dpi, 512x256 inches, 128feet, 4dpi, 1024x512 inches, 2dpi 256 feet, 2048x1024 inches, 1dpi gives a viewing distance of 512feet and a print size of 4096x2048inches.. 340 feet long by 170 feet high..

There's no reason you can't carry on and print at 0.5 pixels per inch, but I'm going to stop, before I run out of ink.

Now, this looks rather fun, we know how big to print this image so it can be seen by an astronaut in the Space Station 200 miles above the earth. Going by my maths, the picture would need to be 1600 miles by 800 miles, and every pixel would be about 170 feet square.

However people don't spend as much time examining a billboard as they do a magazine page, so I'm pretty sure you can drop the dpi down from those figures as distance goes, I've just done a bit of a thought experiment for the heck of it.

[ravncat]

Originally Posted by SwissJon

Thanks Ravncat.. So you're saying that the printer has a native resolution, just like a monitor.. I guess that makes sense. I've an Epson, I'll stick to those resolutions.

Ink jet printers use "microdots" to of color to create more than two tones and that's usually the resolution that you see stated on a printer box that says something like "1440 dots per inch." So in order to represent more than two tones, the dots themselves have to be arranged into "cells". Larger cells grant more tones, but smaller cells grant more resolution - so there's a tradeoff. (Books are written about this) So, in general, the cell size must be an integer - This is where that native "resolution" for the printer comes from. (The relevant wiki link Dots per inch - Wikipedia, the free encyclopedia )

This illustration by Rags Gardener shows how the Rastering process (done by the software) converts pixels into cells.


As you can somewhat imagine, by feeding the native cell resolution directly to the printer, there's a 1:1 correlation between pixels and dots, which means no math for scaling, and you don't end up with printer scaling artifacts (nearest neighbor scaling occurs) The cell sizes are usually also "optimized' for the ink spreading that occurs when the ink hits some standard reference paper (So because we don't know what that is and use many papers - that's a pain in the but to take into account) The native "cell resolution" will give the cleanest fine details.

Hopefully this gives a clear idea as to why you end up with better results using the native number - Although, Mathematically, printing at double that resolution should work fine as well if you need to upscale for really large prints - but there's not going to be much benefit over the native resolution itself. Halving the resolution (ie 180 on epson) should give good results as well, except that you may likely throw away data (or printers with an odd number of cells) , and you'll find that up sampling with photoshop that's not too extreme produces results that are incredibly similar.

I've seen several sources that state epson (at least the r2880 and my old 1280 (and some of the other "photo" printers have come up in searches on this topic) have a native 360 dpi.) For a non Epson printer, you'll have to google search. I first ran into this phenomenon in "Fine art printing for photographers by UweSteinmueller and Juergen Gulbins

[Biomech]

So you're saying that the printer has a native resolution, just like a monitor.

I don't see how, as the print jet has a single nosel and just fires the ink out in the "resolution" specified

[sk66]

Originally Posted by Biomech

I don't see how, as the print jet has a single nosel and just fires the ink out in the "resolution" specified

It would be more accurate to say it has a "maximum resolution" just like your monitor.

Jon,
I like that the article says nothing about changing the image size (pixels) in order to reduce print size; because you shouldn't in most cases. Don't confuse the "printer resolution" with what you "should use"...it's the minimum resolution you should use to get the best image quality from the printer.