How to export edited photo using DPI sizing?

[Stumped]

Lightroom Version

Version 6

Operating System

1. macOS 12 Monterey

I use an online program that requires .jpg scans to be uploaded at 762 dpi.



Here is an example of the Test scan at 762 dpi

I use Canon Scan utility to scan the image at 762 dpi. here are the settings on export.

I have exaggerated the image tilt for illustrative purposes. The E gauge program also requires the image to be squared up in order to get a proper measurement. I can do that in LR, but, Question:

How do I export the edited and squared up image while also keeping it at 762 dpi? I dont see that option as a choice for resolution?

 

[Johan Elzenga]

Change pixels to inches or cm. That will give you the option to specify the PPI (not DPI, images do not have dots).

 

[Stumped]

So do I then need to convert to DPI ?

 

[Stumped]

Change pixels to inches or cm. That will give you the option to specify the PPI (not DPI, images do not have dots).

So is PPI and DPI the same Resolution ?

 

[Replytoken]

So is PPI and DPI the same Resolution ?

They are not. That is why Johan suggested converting to inches or cm. Once you set this and set the DPI, LR will do the calculations for you based on the resolution of the original image and the quality of output you select. It is generally not a 1:1 correlation.

--Ken

 

[Stumped]

They are not. That is why Johan suggested converting to inches or cm. Once you set this and set the DPI, LR will do the calculations for you based on the resolution of the original image and the quality of output you select. It is generally not a 1:1 correlation.

--Ken

I guess thats what im trying to figure out - I dont see DPI in the LR settings?? So do I convert some how 762 to in/cm outside of LR??

 

[Johan Elzenga]

DPI is simply the wrong term when talking about digital images. DPI stands for ‘dots per inch’, but digital images do not have dots. They consist of pixels, so the correct term for digital image resolution is ‘pixels per inch’ (PPI). You can consider them the same in this case. By the way, if you read the instructions carefully, you will see that you need to scan at 762 dpi. That is only to get the correct size in pixels. The PPI setting is irrelevant and there is no requirement to keep that at 762.

 

[Stumped]

ok, tks. so do I want in, cm or pixels?? I guess if Canon and the e gauge are both using DPI terminology, I keep it in inches? I did see online a conversion chart that read DPI = PPI. I guess its confusing that both Canon and the e gauge are using inappropriate terms. So when I changed the LR settings to inches, I got this:



Which I hope is 762 "DPI"

 

[Replytoken]

ok, tks. so do I want in, cm or pixels?? I guess if Canon and the e gauge are both using DPI terminology, I keep it in inches? I did see online a conversion chart that read DPI = PPI. I guess its confusing that both Canon and the e gauge are using inappropriate terms. So when I changed the LR settings to inches, I got this:

View attachment 20361

Which I hope is 762 "DPI"

You can consider them the same in this case.

For the sake of simplicity, you can follow Johan's advice that I have quoted above.

And if you printed the file above at 762 DPI, you would get a print that is 1.02x1.11 inches. If that suffices, then you are good to go.

--Ken

 

[Stumped]

By the way, if you read the instructions carefully, you will see that you need to scan at 762 dpi. That is only to get the correct size in pixels. The PPI setting is irrelevant and there is no requirement to keep that at 762.

So if I have scanned at 762DPI, make my adjustments, I still need the export from LR to be at 762 dpi to then be able to upload to the eguage. So what is the process to keep the image at 762DPI?

I still done understand what to make the LR setting to accomplish this on export?

 

[Conrad Chavez]

I guess thats what im trying to figure out - I dont see DPI in the LR settings?? So do I convert some how 762 to in/cm outside of LR??

No, what the others are telling you is that if you change units to Inches, a PPI field appears, and you set 762 in that. You will then get 762 PPI…as long as the Inches value is correct. Both values have to be correct because if you want “pixels per inch” than the number of pixels and number of inches both have to be entered correctly.

ok, tks. so do I want in, cm or pixels?? I guess if Canon and the e gauge are both using DPI terminology, I keep it in inches? I did see online a conversion chart that read DPI = PPI. I guess its confusing that both Canon and the e gauge are using inappropriate terms.

For the purposes of this discussion, PPI and DPI are the same thing. So if you entered both a correct Inches value and a correct PPI value, you are done.

However…

If you want the “inside baseball” explanation, technically PPI and DPI are different, as part of standard professional printing terminology:

• PPI. Pixels per inch, or the number of image pixels per inch of physical dimensions as printed.
• DPI. Dots per inch, or the number of hardware dots that the printer can lay down per inch.
• LPI. Lines per inch, or the number of lines of halftone screen dots per inch (not all printers use a halftone screen though).

So you could, in the same job, print one image at 300 PPI at a 150 LPI screen on a 2400 DPI prepress platesetter. On screen, every day millions of people view images saved at 72 PPI on their smartphone screens that are well over 300 DPI.

But again, in general use, people and companies interchange PPI and DPI all the time, just because most people don’t know that there’s a difference.

 

[Stumped]

For the sake of simplicity, you can follow Johan's advice that I have quoted above.

And if you printed the file above at 762 DPI, you would get a print that is 1.02x1.11 inches. If that suffices, then you are good to go.

--Ken

Ok, I guess that answers it. Change to inches and dpi=ppi. Just keep at 762. Tks.

 

[Conrad Chavez]

So if I have scanned at 762DPI, make my adjustments, I still need the export from LR to be at 762 dpi to then be able to upload to the eguage. So what is the process to keep the image at 762DPI?

What is confusing about this is that if an image comes in with a ppi value embedded in it, Lightroom doesn’t pay attention to the ppi value, and doesn’t preserve it like Photoshop does. (This is a side effect of Lightroom having a different philosophy than Photoshop, again related to Lightroom not being set up for printing at all.) So if the scanning software embedded “762 dpi” into the image, that value is not reported in Lightroom even if it’s present in the original file, so when you export, you have to enter ppi and inches again as you did in the scanning software. Which would be a problem if you did not know the original physical dimensions of the object.

In this specific case, you do know. The way to get it right is to look at what you posted in your Canon Scan screen shot:
1.11 inches wide at 762 dpi

So that is what you want to enter when exporting from Lightroom:
Long side 1.11 inches at 762 ppi

As long as the original object is actually 1.11 inches wide, that should export as you expect.

 

[Stumped]

Ok, I guess in that light , it opens a whole nother can o worms…. The image including the black outline or just the stamp part that the e guage reads when uploaded? I’m guessing LR won’t differentiate between the 2? In that case I’ll have to physically measure each stamp before scanning? Or at least know the size of an actual stamp before it’s cut or used? Ie, as new….

 

[Conrad Chavez]

Reading the e-gauge requirements in the first post, the whole point is definitely to allow them to know the precise physical size of a stamp. If they define that as the stamp paper, edge to edge, no background included, then you want to measure that with a real ruler and write it down before scanning. After that, you can crop and rotate it without having to think about the numbers (there is no need yet), and then when exporting, you specify the inches you measured with the real ruler, and also you specify 762 ppi.

Note that the image crop must exactly equal what was measured with the ruler because it’s the only reference for physical measurement. (Unlike Photoshop, Lightroom has no on-screen rulers for physical measurement calibration.) For example, if you measure the stamp edge to edge but the final export includes a little background, then the exported file width will not be the same as the measured stamp and the resolution will be incorrect. So it should work, as long as you’re consistent.

 

[Stumped]

Got this back from Adobe where they say LR retains the value.

“ Lightroom retains the DPI of the image. DPI refers to the number of printed dots contained within one inch of an image printed by a printer. PPI refers to the number of pixels contained within one inch of an image displayed on a computer monitor. DPI is used by Printer and PPI is used by Lightroom. DPI and PPI are equivalent so 762 DPI is equivalent to 762 PPI. “

 

[tspear]

Got this back from Adobe where they say LR retains the value.

“ Lightroom retains the DPI of the image. DPI refers to the number of printed dots contained within one inch of an image printed by a printer. PPI refers to the number of pixels contained within one inch of an image displayed on a computer monitor. DPI is used by Printer and PPI is used by Lightroom. DPI and PPI are equivalent so 762 DPI is equivalent to 762 PPI. “

Umm, maybe. Here is the problem with that statement.
I have a 4K monitor at home which is 30in diagnal.
I also have a 4K monitor on my laptop which is 17in diagnal.

Somehow, I do not think the PPI is the same on the two monitors.

Tim

 

[Stumped]

So as mentioned I believe I figured out my original question. But the reply from adobe is what makes all this confusing. As well as canon using dpi in their software and then ppi on others. Anyhow, all good. I thought it’d be a good fyi for here.

 

[Conrad Chavez]

The Adobe tech’s answer was confusing, but can probably be explained.

Lightroom Classic does retain the resolution; it won’t change the PPI value in the original file’s metadata. If the metadata in the file says 762 ppi, it still says that after Lightroom Classic catalogs it. But the reason that’s not useful is that there is no way to get at that ppi value in Lightroom Classic. The PPI resolution of the file metadata is not shown (unlike Adobe Bridge and Photoshop which do), and it is not available to be selected on export. So in practical usage, you still have to go in there and tell it what ppi value to use at export because it is not going to get it out of the file.

When the Adobe support person (probably a lower level tech) says PPI and DPI are the same, they probably mean that most people do use them interchangeably because the difference isn’t generally recognized (mostly just by technically precise industry specialists), and for your purposes they do mean the same thing. But in its software Adobe goes by the book, so if you look through Adobe applications such as Lightroom Classic, Photoshop, Bridge, Camera Raw, etc. they correctly label it PPI, not DPI.

 

[Johan Elzenga]

This thread is about Lightroom desktop, not Lightroom Classic. Of course that does not change what DPI or PPI mean, and I don’t think Lightroom desktop shows PPI either, but the export dialogs are different in this respect.