Lightroom Classic 9.1: Export jpg to jpg; cannot change resolution (Windows 10)

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I scanned jpg images in full res of the scanner (4800 ppi), worked on the images and exported with the setting to max resolution 1920 pix per longer side. No matter what I tried, all exports were done with the original resolution. Is this a bug or am I missing something in the settings?
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Timo Ihamaki

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Posted 2 months ago

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Andrew Rodney

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Original resolution isn't the same as original number of pixels. Did you get 1920 pixels as requested?
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John R. Ellis, Champion

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Please post a screenshot of you Export settings window.
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Apologies for being inconsistent with the terms, resolution / dpi, they are interconnected anyways. Originals were standard 24x36mm slides, scanned with max resolution, resulting in roughly 6400x4300 pix files. As output I wanted to have images with max 1920 pix per longer edge. Here are the settings of the part of the export dialog that handles resolution/dpi. 

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Carlos Cardona

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What I remember hearing in a photo podcast is that the resolution setting in the image sizing section is completely useless, changing those numbers does nothing, means nothing.
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I would quit listening to that podcast as it is a false statement that the resolution does and means nothing. 
A couple reasons:

1) The resolution setting gets written into the export file metadata and this info is used in other programs such as Photoshop for automatic sizing purposes.

2) Resolution in the Lr export dialog is used when you use the "INCH" and "CM" criteria so Lr can automatically calculate the pixel dimensions of the export.
(Edited)
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Well Robert, I just tried exporting the same photo with different resolution settings and, guess what? The exported jpg size is EXACTLY THE SAME regardless of what resolution settings you use, whether 1 PPI or 4800 PPI! Go ahead, try it!

This proves what the podcast said, the field isn't used, LR decides the best PPI for itself. Go Podcasters!
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Try this.   Guess what, the file sizes are different DEPENDING on the Resolution Setting.   Your Podcasters are misleading you.

Export #1 dialog settings with resolution 300

File info




Export #2 dialog settings with resolution 100

file info
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You might wish to try this again. When I export a document with a FIXED pixel dimension but with 240 vs. 2 PPI in LR, the export is IDENTICAL except for the resolution tag (240vs2). As I expected, the value for pixels IS honored in LR's export, both exported images have identical number of pixels, they are the same size, the only difference is the resolution tag. As I expect, this tag has absolutely no bearing on the data other than this tag. An export at 1000 pixels at 240PPI is identical as an export at 1000 pixels at 2PPI. And as you can clearly see, the screen captures above show a different pixel dimension so yes, those two documents are radically different as expected.
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I agree 100% in your scenario Andrew but if you would have read closer I was exporting with "Resize" using "Inches" and "Long Edge" in the "Image Sizing" section and in that scenario the "Resolution" serves a useful purpose and is NOT useless a Carlos suggests.

The "Resolution" setting is also, as in your scenario, stored in the exported file and is useful when using the file in other programs such as Photoshop that honor this resolution when importing and can be automatically resized the the canvas psi settings.

I find the "Resolution" setting in Lightroom to be useful in special occasions and so do many others.
(Edited)
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But if resize is or isn't selected, the podcast is correct that PPI settings have no effect on the exported size; it's only the pixel dimensions that matter. And the resolution tag isn't very useful anywhere if you simply work in pixels.

You wrote: "Guess what, the file sizes are different DEPENDING on the Resolution Setting".

NO, that's not so; the difference is based on the number of pixels exported, not the resolution tag as I illustrated. The response would make much more sense if you wrote: "Guess what, the file sizes are different DEPENDING on the Setting for pixels which change if you select a size (in inches)". The resolution field you show above as 100 vs. 300 have zero bearing on the exported size in pixels per se. When you change the pixels, and you indeed did, it does have an effect of course (PPI and output size in inches).
(Edited)
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Andrew,  do the export with the EXACT export dialog settings I have shown and you will see you are wrong.  The file size/pixel dimensions are dependent on the resolution settings in the dialog and do change!  Unfortunately you have not bothered to look closely at my original post and are on a completely different export scenario.  
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"What I remember hearing in a photo podcast is that the resolution setting in the image sizing section is completely useless, changing those numbers does nothing, means nothing."

It doesn't per se, it depends on if the software is looking at that value AND using interpolation to size up or down that data into a set of pixels. The tag alone does nothing. It's used to provide a 'size' on a print, or display or if the software is asked to resample, it can be used to achieve a 'size' or a number of pixels HxW (8x10 at 300PPI vs. 8x10 at 100PPI) but if you simply work in pixels, the tag has no real meaning or use. IOW, 2400x3000 vs.1600 by 2000 pixels is what the document contains in pixels no matter the tag. That 'size' will differ if you alter the division of the pixels you have (lay out 1000 pixels per inch using either 2400x3000 you get 2.4x3 inches).

You have 2400x3000 pixels. That's all that's important. It doesn't matter if the tag shows 72 or 300 or 1000, it's still 2400x3000 pixels. You can divide them up any way you desire to calculate a possible size. You can resample (add or remove pixels) and of course, now you have more or less pixels to deal with no matter the tag. So yes, if you have 2400x3000 pixels, changing those numbers does nothing alone but allow the software to tell you a potential size using that tag as the source of division of said pixels. 
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Andrew,  do the export with the EXACT export dialog settings I have shown and you will see you are wrong. 

We're talking across each other and not helping Carlos. The tag alone does nothing. That part of the podcast is correct as is Carlos understanding. The tag used with a value for producing MORE or LESS pixels does something. Carlos was told something about the resolution tag that is actually true; unless you go out of your way to add or remove pixels, the tag doesn't change the data whatsoever in terms of pixels. YES, you can tell LR or Photoshop that you have a 100PPI tag inside a 1000 pixel document and to make more pixels (or less pixels) and yes that changes the size and of course pixels. But the tag alone doesn't when you don't resample and simply alter the value of the tag. 1000x1000 pixels at 2 PPI isn't any different than 1000x1000 pixels at 1000PPI. It's still 1000x1000 pixels. 
IF people work solely with pixels as I think they should, the tag is absolutely meaningless. You want more or less pixels, just specify the number you want. Done. 
(Edited)
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Yeah, what he said! ;-)

I don't remember which podcast, Marquadt, The Northrups, Komarechka, Sharky, B&H, Master Photography, Brazill, those are the good ones!
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Yeah, what he said! ;-)

I don't remember which podcast, Marquadt, The Northrups, Komarechka, Sharky, B&H, Master Photography, Brazill, those are the good ones!
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"resolution setting in the image sizing section is completely useless, changing those numbers does nothing, means nothing."

But I have shown that they do something (export using inches/long side in the export dialog) and mean something (the tag to others programs like photoshop).  I use the "inches/long side/resolution"  combo a lot and let Lr calculate the final pixel dimensions of the export.  If you and the podcast person don't understand the usefulness then don't use the resolution setting.
(Edited)
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But I have shown that they do something
No, you showed that you've interpolated the data; as the size in pixels between the two differ. As your screen shots clearly show. Just as if you worked solely in pixels and made or subtracted more or less pixels. 

Again, IF you work in pixels, there's zero need to be concerned with the tag. It ONLY provides a 'size' based on it's current value where as working with pixels (and understanding simple math) allows you to figure out ANY size with the current number of pixels or pixels you add or subtract. And the facts are again, as Carlos understands. There is NO DIFFERENCE between a 1000x1000 2PPI document and a 1000x1000 300PPI document. The tag is meaningless, the number of pixels are not at all meaningless. 
(Edited)
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I didn't interpolate the data, Lightroom did, by using the resolution value in the export dialog.  If you try the setting I have shown yourself you will see you are wrong that the resolution setting in export does nothing.  DONE
(Edited)
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I didn't interpolate the data, Lightroom did,

OF course it did interpolate as you allowed it to do so. 

Do you own Photoshop? It would be simple to illustrate how this all actually works if you do and understand it's Image Size dialog. 
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I have always understood and therefore taught (see "Lightroom Myth Buster: When Resolution Matters and When It Doesn't") that changing resolution when sizing in pixels doesn't affect anything (other than changing the tag), but I have recently heard that because PPI is part of the output sharpening algorithm, there will be a difference in sharpening levels. That said, I haven't seen any difference in the comparisons I have done. Andrew, do you know anything about this?
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Here's a year-old thread where Richard Plondon stated that PPI affects output sharpening:
https://community.adobe.com/t5/lightroom-classic/export-ppi-and-file-size/m-p/10119861#M123826


I just did an experiment, confirming that PPI does indeed affect the output sharpening.  I started with this image:



I exported it with Sharpen For: Matte Paper, at PPI 100 and PPI 600. I then opened the two exported images as layers in Photoshop, taking the difference between the layers and changing the white point of Levels to visually highlight the differences:



The differences are all at the high-contrast edges, which is what you'd expect if PPI changes the sharpening.

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The Lightroom Classic Help says:

"The amount of print sharpening that is automatically applied is based on the file’s output resolution and the output media."
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 Andrew, do you know anything about this?

I wrote my first article for a magazine on Resolution way back in 1998 and I see it's still a topic of confusion today. FWIW, the article is archived here:
http://digitaldog.net/files/Resolution.pdf

Let's start here with some caveats and why I suggest always working in pixels. 

1. Digital images don't have any size other than the space they take up on some storage media. This size varies by many attributes even if the document has the same number of pixels: bit depth, layers, file type and possible compression, color space. It's not worth even considering this size due to so many differences. Digital images therefore should be considered in pixel density. And for this discussion I'm going to limit this to one axis (let's say the long axix) and the image is 1000 pixels. 

2. An analogy is necessary to discuss the resolution tag in digital images. If I'm 6 feet tall and every stride I take is 3 feet, and my friend is 5 feet tall and every stride he takes is 2 feet, when we both walk exactly 1 mile, we walked exactly a mile. That I walked with less strides (resolution) doesn't change that I walked exactly 1 mile (pixels). 

3. The resolution tag places no role in the 1000 pixel document in this respect: 1000 pixels at 100PPI and 1000 pixels at 100PPI are the same: 1000 pixels. In fact you can take a document that has 1000 pixles with a resolution tag of 100PPI, duplicate it and change the resolution to 1000PPI and the two are identical other than for metadata such as this resolution tag. And of course metadata like date/time the document was created and so forth. The two documents are 1000 pixels and the tag has no role and does nothing at this time. Set it for anything you want, as often as you want, it's the same digital image at this point. 

For all intent and purposes, the resolution tag plays no role. The number of pixels does. But wait you say, "I want to output the 1000 pixel image". To a print or on screen. OK, now we have a new size to consider! Let's work with a print. Computers are not too smart, they have no idea what you wish for a print size until you tell it. They do know you have 1000 pixels to use to make the print. What size print do you want? The answer comes about when you divide up the pixels you currently have (more about what you might have later) for this print. Now size can be inches, feet, meters, miles, CM, MM you get the point. Let's stick with inches for this story. You have 1000 pixels and the resolution tag is set to 100PPI. You simply need to understand simple math (division) or have a calculator once you accept you have 1000 pixels. At 100PPI (the tag), a print could (repeat could be), 10 inches. If the tag is 1000PPI, you're going to end up with 1 inch if you allow the computer to provide that division of your pixels. If the resolution tag is 23PPI, the size would be 43.4783 inches (here's where a calculator is useful). It's not if the tag is in MM or CM, or you alter the tag value. But in every case, the data is 1000 pixels. That is the critical number to know about first. The other number can always be changed so software can at this point understand a potential size for output. 

OK, so now Lightroom (or Photoshop or anything else) comes into play. And you ask for that 1000 pixel document to be output to 10 inches at 200DPI. What's a computer and software to do? You don't have 2000 pixels. So the software will interpolate and add more pixels out of thin air so to speak. Or you could reduce the number of pixels with interpolation. This is where Robert got a big flummoxed. He said "I didn't interpolate, LR did". Of course it did! If you ask for output that requires 2000 pixels and you only have 1000 pixels, AND you give the software permission to make more pixels, it will. It will interpolate. It interpolates because you told it to interpolate and make more pixels due to the size relationship with the current tag. 

Now to the deal with sharpening. Until you print the image, it's still 1000 pixels. The PPI tag is moot. But you asked in the print module for a print at a specific size. And guess what, LR sharpens based on what it knows about the number of pixels (current or what you might, repeat might interpolate) and the size you asked for. Output sharpening is output resolution and size specific. So that tag is NOW used. But you still have and have always had a 1000 pixel document san's permission to interpolate adding or removing pixels. 

Work in pixels. Have a calculator nearby if necessary. Pretty much ignore the resolution tag until, if, you need to output that data and you require a specific output size or sharpening in the case of LR. Understand you can allow software to interpolate BASED on the resolution tag. If the tag is 100PPI and you tell LR you want 10 inches, the results are quite different than if the tag is 1000PPI and you tell LR you want 10 inches. You are in control. The software only looks at the tag if and when you tell it to look and use that tag to produce some size with the pixels you have.  
(Edited)
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WHY would anyone want to get a calculator out when there are tools in the Lightroom export dialog, the resolution and inches/cm settings, that will do the calculations for you.  
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Because Robert, not everyone is using LR, not everyone understands when and where interpolation will take place as we've heard, and most importantly, nowhere in that export dialog with any of the options does LR tell you the native (actual) number of pixels of the selected image let alone if you select multiple images of differing pixel dimensions. 

Here's the export dialog, I've selected one raw: what's is its actual pixel dimensions? 


What's kind of important that someone might have missed is the "Don't Enlarge" check box which gives LR permission to interpolate. 
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Lightroom export dialog, the resolution and inches/cm settings, that will do the calculations for you.  
Can you therefore explain the calculations below and based on the number of pixels in the original?


Width is 10.5 at 72PPI but....

Width is STILL 10.5. 

Seems a calculator might still be useful for some who would like to know the resulting number of pixels but it's not going to help decide how many we have to work with. 
Note too, that WxH is NOT the original aspect ratio of the raw selected. It's sticky from the last setting and doesn't honor the actual image itself. 
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I agree Andrew.  If for instance I have photo cropped in LR that is 3000X2000 and tell Lightroom to export with a Long Side of 20 inches and 300ppi with the Don't Enlarge checked LR will happily export the file at 3000 on the long edge and not tell me it did not meet the 300dpi criteria.  It should bring up an error dialog on export telling you it doesn't meet my needed criteria.  I always use the inches/resolution settings when exporting for a print lab but always check to see if I have enough pixels for my intended purpose after the export with a quick mental calculation as Lr doesn't tell you this.
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This seems like a bug. If I ask for a 12000x12000 pixel export and Don't Enlarge IS Checked to be on, I still get a 12Kx12K export from an original that clearly isn't that size in pixels. Kind of begs the question; what's the use that check box if it's not going to warn you and it's going to go ahead and interpolate the original upon export. 

CORRECTION: The exported file isn't 12Kx12K, it's full resolution of the original. But LR doesn't pop a dialog telling you this. So it's not really a bug, but poor design. 
(Edited)
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Andrew,
I am not seeing that bug.  If I export using the following the resulting exported file is the original dimensions of the smaller file.  Lr 9.1 and macOS 10.14.6

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Sorry I didn't see your corrected post before I posted
(Edited)
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IMHO, with the setup above, LR should pop a warning and tell you:
1. You're not going to get 12Kx12K. If you want that, turn OFF "Don't Enlarge". 
2. You ARE going to get WxH of the original and show you this number of pixels in the dialog. 
So it's not a bug. It's poor design. 
I just placed a feature request for this. 
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Thanks.  That would be a welcome feature!!
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So, photo podcasts are a good thing! ;-)
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So, photo podcasts are a good thing! ;-)
Yes.
No.
Yes.
She's my mother, she's my sister, she's my mother, she's my sister...
You get the idea Jake <g>. 

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Took me a few seconds to realize you were a Chinatown fan. : )
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What is the correct way to export a photo to a smaller size?
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I just tested exporting with Resize To Fit: Long Edge, 1920 pixels, and it worked correctly in my LR 9.1 / Windows 10.  

Try resetting LR's preferences: https://www.lightroomqueen.com/articles-page/how-do-i-reset-lightrooms-preferences/

LR not infrequently soils its preferences file, and resetting it can fix all sorts of wonky behavior, including Long Edge not working:
https://feedback.photoshop.com/photoshop_family/topics/-broken-lightroom-export-resize-to-fit-long-edge
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Thank you for the advice! Resetting LR settings was the solution. Also another issue was solved where importing images with "copy as DNG" didn't convert files into DNG. And as additional information, at least I didn't have to re-apply any deeper settings in the LR, only something like turning the solo-mode on. 
(Edited)
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Glad you got it resolved.