Lightroom Classic: Pixels per inch not possible

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LR Classic CC has (when you export a file) the option "Resolution - ___Pixels per inch". But why? A digital file does NOT have a size in inches.
I would remove that option because it does not make any sense.
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Dolf van Stijgeren

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Posted 11 months ago

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Ruurd van Dijk

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It is indeed only a property of the output-device (printer, screen), NOT of the digital image. Everywhere I see this strange discussion emerging...
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Dolf van Stijgeren

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I am not quite sure what you mean. You can export the file to 1) email 2) Harddrive and 3) CD, but not to a printer. The "Resolution" option is underneath "Image sizing", but it what ever one fills out, it does not influence the size of the image.
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Robert Somrak, Champion

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I don't know why people get hung up on digital files not having inch dimensions so by extrapolation then get rid of the dpi/ppi setting.   There are at least a couple uses for that option and I am sure several more..

1) The digital file may be printed at a lab.   If you want a file at 300dpi and 8x10 inches you can enter those numbers and Lightroom will do the calculations for you.

2) When you use digital files in some other programs the dpi/ppi value is used to size the file in the other program.


(Edited)
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Dolf van Stijgeren

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1) A file is composed of pixels - NOTHING else. The thing is LR does not change anything when you change the pixels/inch setting.2) A file does not have any dot.
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Robert Somrak, Champion

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I think you missed the whole point of the uses for ppi/dpi in the export dialog.

1) actually a file contains a LOT more info than pixels and one of them can be PPI or whatever the "official" metatag is that other programs use to initially handle the file on import.
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Andrew Rodney

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Exactly, like printing (out of Photoshop among many other applications). 
Or the OP can assume everything is 72"DPI" as we've seen in the past and isn't at all useful or accurate. 
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richardplondon

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This setting does indeed have a meaning even if it does not (directly) change the pixel content of the file.

Firstly, this may simply be another way to set the properties of the digital image which is output - but it may also an indication of the INTENT behind a particular outputting of the digital image - of its usage and purpose.

If you type in 1600 pixels wide (and 400ppi, or 4ppi), this is effectively the same thing so far as the pixel dimensions alone, as typing in 16 inches wide and 100 pixels per inch - or someother combination.

However setting 400ppi denotes an image which is envisaged (intentionally, or incidentally) to be printed to a smallish size range, and 4ppi denotes billboard size. 

How does this envisaged sizing matter?

It matters to Lightroom itself, for one: if you set output sharpening, this will happen differently (different picture content resulting in those two cases) even if the pixel dimensions remain the same. In Photoshop also, if you zoom the image to "print size" on screen; or if you use a physical size related means of cropping/converting or printing.

Another difference comes, with the placement of the digital image into other page layout software, or a similar technical / prepress workflow. Here physical scale is often intrinsic to the working method. For example: commonly a screen-resolution preview is made internally @ say 72ppi. If this image starts @ 4ppi, a 72ppi preview version will turn out much larger than the image itself; affecting file size etc for the working document. If it starts @ 400ppi, the 72ppi preview's a more useful and sensible version of that.

Hence a certain PPI is often asked for as well as a certain pixel dimension; and this is a good idea to deliver, EVEN IF the means one is actually using to determine these pixel dimensions in the first place, is by typing them in directly. 
(Edited)
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Dolf van Stijgeren

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As I said before in other comments, a digital file is composed of pixels. - nothing else. When you change the setting "Pixels per inch" it does not change anything in LR (in PS yes, but then it is called upsampling). That is why I posed the question.Of course I realize the effect of number of pixels in relation to the size of a print, but LR does not know - so to speak - the size of my print.
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richardplondon

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BTW changing PPI in Photoshop does not need to involve any upsampling (or downsampling) of the pixels. One can just change Resolution: the notional print size duly alters - when Resample is unchecked.

Even though it's not pixel data per se, PPI metadata IS a required property for a digital image, even more so than its colourspace metadata is. A digital file composed solely of pixels and truly "nothing else", could only be opened in PS by guessing at this missing metadata. For example, PS has got a raw file import utility (nothing to do with camera Raw).

Lightroom DOES know presumed sizing for your output, so far as that has been expressed in the PPI figure given during export. It is not possible to put no PPI whatever (it is only possible to not care what this figure is). LR can't know whether you agree with this notional sizing, but that's not really the software's fault: it is only following the available clues in a logical manner.

And this sizing then affects the output sharpening (if used). That's because it declares the particular (physical scaled) target circumstances which this sharpening should address. And this in turn changes, slightly, the actual pixels included in the output file.
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Andrew Rodney

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The setting absolutely has a meaning and is necessary. You could argue that the metric (inches) should be something else like millimeters or centimeters or even the old Rez (rez 12 etc). The file is made up of pixels so pixels per whatever makes total sense. Using 'dots' wouldn't be technically correct. We need to know the pixel density we desire so pixels per inch tells us this critical information. Again, you might wish pixels per mm but none the less, Adobe absolutely shouldn't take your suggestion to remove this. 
You seem to need a primer on resolution:
http://www.digitaldog.net/files/Resolution.pdf
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Dolf van Stijgeren

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Ryan: do you agree a digital file is composed of pixels? I said "nothing else" in the context of "pixels per inch".
(Edited)
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Andrew Rodney

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Are you really serious? "Once you print you can check the number of pixels per inch"? You'd do that how and why on earth would you do that AFTER making a print. Look, this is getting to be rather silly (CWOBaT (colossal waste of bandwidth and time). You again seem confused by what and why LR tells us about pixels per inch and have asked Adobe to remove it. That's not going to happen for all the reasons, and more, expressed here. I again suggest you educate yourself on what LR is telling us, examine the multitude of other software products that deal with image data that report the same metric as LR does. FOR GOOD REASON. Once you actually understand what and why these products do what they do, maybe you'll see why virtually no one here is taking your ideas seriously. 
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Robert Somrak, Champion

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Andrew, I like the CWOBaT.  Haven't seen that one before.
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Dolf van Stijgeren

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I don't take your advice but would like to the opportunity to explain what I meant with "Once you print you can check the number of pixels per inch". I mean once you make the DECISION  to print, you decide on the size of the print and THEN you know the actual number of pixels per inch.But can you please explain WHAT LR exactly does when you set the pixels per inch and how it would change the digital file? 
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Andrew Rodney

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Explained multiple times. If you refuse to read and learn what multiple people report, we can't help you.
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Ryan Smith

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You do realize digital files can be printed correct? 
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Andrew Rodney

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It changed the Metadata tag!
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Ryan Smith

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The answer is in the question! If you aren't printing don't worry about this option it won't do anything, it won't hurt you either so just ignore it.  You can Google all this stuff by the way. I do agree though that Adobe should make this option a little more clear.
(Edited)
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Robert Somrak, Champion

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I test it every time I open a file in Photoshop because Photoshop uses the PPI setting used in the Lightroom Export Dialog.  I think this thread has exceeded it useful lifetime.  
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Robert Somrak, Champion

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Ryan
This setting is also useful for files used in other programs such as Photoshop that read the Metadata tag.
(Edited)
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Dolf van Stijgeren

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Why would one set the PPI to change the meta data? My point is that it is useless to change the PPI in LR, but if you think it affects the number of pixels and enhances the print quality, be my guest..
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Koro

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It's all been said above and there's probably no need to stir the pot but the option does make sense and it shouldn't be removed. I use it frequently. Indeed, I have constructed a collection of presets that are built around its use and I'd be a little miffed if the option were removed.
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Ruurd van Dijk

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Test for yourself. Save a file with just 1 PPI, and save the same file with 100000 PPI. Compare the results. There is no difference!! So this is a useless option!
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Andrew Rodney

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Exactly Robert. And here's a perfect visual example for Ruurd and Dolf. This image was exported from LR at 300 pixels along the long axis. They have the identical pixel DENSITY along the long axis. One was tagged at 300PPI, the other at 72PPI. My display happens to be 109PPI (no Ruurd and Dolf, all displays don't output 72PPI and it's easy for anyone to figure out the exact resolution IF you want to know how). You see a screen capture where Photoshop uses the PPI tag to show us the 'print size' on screen but this would take place in many, many other applications that SIZE the output on a screen (or print) based on this very important metadata tag:



Ruurd and Dolf; see a difference above? Both documents are IDENTICAL expect for the tag you guys don't seem to think is important but clearly it is. I hope this puts this silly debate to rest. The tag plays a role. It's there for a reason. YOU two may not yet understand when or why it's there but none the less, it's there for a purpose that absolutely is used and does affect how that same 300 pixel image is handled. 
(Edited)
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Andrew Rodney

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>>Test for yourself. Save a file with just 1 PPI, and save the same file with 100000 PPI. Compare the results. There is no difference!! So this is a useless option!<<

As you can see above, your testing methodology is faulty. Try again. 
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Ryan Smith

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I've lost interest in this, if someone wants to think Adobe just has a pointless dialog box for years in their software and he was the first to figure it out, I really don't care.  
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Dolf van Stijgeren

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We can all agree a digital document is composed of pixels: 3000x2000, 6000x4000, 5472x3648, etc, etc, etc. When you want to print, the number of pixels is important and usually 300 ppi is required. 
I have exported two identical files in LR and changed the "resolution" (the number of pixels per inch): 72 and 300. As you can see in the EXIF the actual size (5472x3648) is exactly the same. Strangely enough Apple says DPI..

Please take you time and read this (as Ruurd mentioned before): http://www.dpiphoto.eu/dpi.htm




(Edited)
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Andrew Rodney

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No! It’s not the same!!!
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Koro

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People, people, people. This is not Facebook... Please don't behave as if it is. Those of you who have an interest in continuing to lob thought grenades at each other, exchange email addresses and do it somewhere else.  Thanks 
(Edited)
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Victoria Bampton - Lightroom Queen, Champion

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Would it be possible to manage without being able to set it in the Export dialog? Yes, because it's just descriptive metadata.

But would that be advantageous? No. Because apart from anything else, when deciding to output a file for print, most people would need to get a calculator out, and the dialog saves you doing that. 

There's a bunch more technical reasons why that metadata tag is useful/important, but even at a simple level it's useful.
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Todd Shaner, Champion

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Victoria has hit the proverbial "nail on the head" and I'll help to drive it home!

While it's true camera files have no real PPI definition this is not the case for scanner image files and perhaps exported files edited for a specific printer and paper size. More at the below link:

https://feedback.photoshop.com/photoshop_family/topics/gw73zjy55amnv

Executive Summary
Scanner image files contain the actual physical dimensions of the captured negative, transparency, photograph, or other 2D document. This file metadata information allows accurate display and print of photograph and other paper document scan image files at a specific target ppi in their actual life-size dimensions. For film scan images it provides a record of the original negative or transparency dimensions enabling identification of the camera format size (i.e. 35mm, 2 1/4, 4x5, 8x10, etc.). This information is required for archival purposes and allows creating and applying Lightroom Develop presets designed for specific film types.

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