PPI settings don't really mean anything in Lightroom. It doesn't matter what the PPI setting is, the image still has the same number of pixels.
It most certainly does matter, when it comes to printing. My printer (Epson 4900) has a "native resolution" (kinda fuzzy for inkjets) of 360ppi. So when I place my image on a print page, it by golly ought to come up as 4"x4". I see no way to tell LR5 to use the data in the file header to determine how big the image is. To arbitrarily choose 480ppi is just wrong. It also tells me that LR5 is going to do an on-the-fly image resize, which, depending on the algorithm used, can introduce artifacts. I made the image at 360ppi SO IT WOULDN'T DO THAT! I have two other printers, "native resolution" of 720ppi and 600ppi. Doesn't matter. LR5 places my image on the output paper as 3"x3". Wrong, wrong, just wrong.
Now, I can manually resize the image to the size I know it's supposed to be, but how do I know LR5 isn't still taking it through an intermediate step of converting it to 480ppi, then sending it to the printer driver, which then has to resize it AGAIN to get it to its native resolution?
Funny. PE11 does it right, but unfortunately, you cannot give it a custom package layout that's bigger than 8-1/2 x 11. My paper is 17x5. So as far as I can tell, neither Adobe product will print my image[s] the way I made it/them.
You are confusing image resolution with printer resolution, and they are different. It doesn't matter what the PPI setting is in the image. It still has the same number of pixels. You just need to make sure you have enough pixels to print at the resolution that you want to print. Changing the resolution setting the image file will have no impact whatsoever.
Yes, agreed, it has the same number of pixels, regardless of the resolution specified in the file header. At the very least, LR5 should use that info to set the scaling it's going to do, so that it sets down on the paper as the size specified. That's just common sense, to me.
But the printer driver wants to send the image to the printer at its native resolution--360 for Epson 4900, 600 for HP 3740, 720 for Epson R3000. LR5 seems to be using 480. So the printer driver has to mathematically scale the image to the proper resolution. This can introduce artifacts, at least when scaling up.
So I give it an image which I know is 5"x5" at 720ppi. LR5 ignores the ppi, sees that it's 3600x3600 pixels, decides that it's 7.5"x7.5". I place it on paper for my R3000, it's too big. I have to scale it down to 5"x5" (possible artifacts). Click Print. Now LR5 sends my scaled image, 480ppi, to the printer driver, which has to scale it UP to 720ppi, still 5"x5" (more possible artifacts). (It's possible that LR5 keeps the original image at 720 behind the scenes; but why does it place it on paper as though it's 480?)
If LR5 recognized the image as 720ppi, it would place it on the paper as 5"x5", no scaling necessary. It would send it to the printer driver, no scaling necessary. This is what Elements does.
Now, I know "native resolution" is fuzzy; the printer still has to take that data coming in at 720ppi and convert it to actual droplets and nozzles at 5760x1440 dots per inch, but it's designed to do that with an input stream of 720ppi. That's optimal. Scaling down and scaling back up is not. Scaling down to 480 is going to lose information. Scaling back up to 720 won't bring that information back.
having trouble...does this get through?
for some reason it won't take my closing argument...still trying...
Huh. Never saw that Print Job menu. My screen is itself kind of wide format, kind of short. I didn't see the scroll bar.
Ok. So presumably LR5 keeps everything device independent until you click Print, and then it renders everything at the chosen print resolution. That's good.
Any idea why it chose 3"x3" as the size to place the image? Just a default, and the result 480ppi just a consequence of that, or is 480ppi built in somewhere? I'll have to try it with images of different sizes and resolutions....
I created 4 identical .psd images 640x360, but tagged at 200ppi, 360, 600, and 720. Imported and placed them on a print page. LR5 showed all 4 as 3"x1.687". Then I created 4 images at 600dpi, but at 640x360, 2X (1280x720), 3X, and 4X. Imported and placed them on a print page. LR5 again showed all 4 as 3"x1.687". Didn't matter if the printer was a 360 or a 600.
So it looks like, at least in my short test, LR5 defaults by placing your image at no larger than 3" in either dimension. So if you want an optimal print, you must both set the Print Resolution to match your printer, AND resize your image on the paper to the size you know it ought to be.
Would be nice if there were an option in LR5 to turn that off (at least for images that have size information built in, like .psd) so that an image that's supposed to be 5"x5" would place that way. Obviously, if the image is too big for the paper chosen, it should scale down to fit or crop, or issue warnings, or both. But, it is what it is.
Thanks, Geoff. I'm going to mark your response as Correct Answer if only because it got me to be confused at a higher level.
I think the key to effective printing in Lightroom is simply knowing that you have enough pixels in the image to justify the resolution at which you want to print. Lightroom gives you complete control over the printing process, enabling you to customize it to meet your exact needs. But you need to be able to do the math to make sure the pixel count is sufficient.
Lightroom is going to fill whatever cell size with the image, regardless of its pixel count if you have selected "zoom to fill" in the image settings. So you have a lot of control in Lightroom when printing. You just need to be aware of how large your image is and confident that you have enough pixels for the size you want to print.