Size and DPI when exporting JPEG

[TanGU]

Hi there,

It's a nice idea to have a forum about Lightroom!

I don't know if i have a problem or if it is normal but here it is... Let say that i shoot 2' pictures (jpegs), and import them in Lightroom, on some of them i will make minor modification, on some no modification and i add some tag, then i filter them by tag, selected them all then export them with the following setting:

• Jpeg
• Quality 1''%
• sRGB
• Resolution: 3'' dpi
• no check on :maximum size, no check on Metadata, no keyword.

Before the export, the file size was 2.9 megs @ 72 dpi, after the export: 4 megs @ 3'' dpi.

I even tried to keep the same DPI as the original picture, and the size is bigger!! even WITHOUT any sort of modification!? Is my picture altered ? why the size change so much even without any modification? i really don't understand that part...

I am so unsure that i've keeped all the original picture + the exported one to be safe because i don't know if it's normal :roll:

Anyone else noticed this?

thanks!

TanGU.

 

[Kiwigeoff]

Are the pixel dimensions on both files still the same?

 

[Clicio Barroso]

Before the export, the file size was 2.9 megs @ 72 dpi, after the export: 4 megs @ 3'' dpi.

There has been quite a bit of talk about this topic in other forums, Tangu.
It seems the JPG encoding in LR is more "conservative" than other apps, and the files are a little bigger.
Do not ask me why, but that's the way it is.
Regards,

 

[Mark Sirota]

The reason why is that Lightroom's JPEG algorithms are less efficient, space-wise, than some others. Also, the metadata may take some space, and it's possible that the original did not include a full color space and the LR output does. (On the other hand, the LR output doesn't include a thumbnail, but the original may have.)

Also, the PPI (not DPI) setting is irrelevant. Completely. If we put together an FAQ (hello, Victoria?) this really needs to be on there.

 

[TanGU]

Are the pixel dimensions on both files still the same?

Hi,

The answer is yes: 3'''x2'''

 

[Clicio Barroso]

Hi,
The answer is yes: 3'''x2'''

That's why the PPI seting is irrelevant...
Regards,

 

[Kiwigeoff]

Hi,

The answer is yes: 3'''x2'''

Then Marks answer is it.

 

[TanGU]

The reason why is that Lightroom's JPEG algorithms are less efficient, space-wise, than some others. Also, the metadata may take some space, and it's possible that the original did not include a full color space and the LR output does. (On the other hand, the LR output doesn't include a thumbnail, but the original may have.)

Also, the PPI (not DPI) setting is irrelevant. Completely. If we put together an FAQ (hello, Victoria?) this really needs to be on there.

Hi Mark,

It isn't clear for me...

So you are saying that LR modify the jpg too much? is it bad ?

I mean , my jpg are originally 72 dpi, if i go and print a picture at...let's say 3'' dpi, then the printer will print it, reducing the picture size. Or will it extrapolate the dpi to go from 72 to 3'' dpi.

Like Lightroom?

this is all unclear for me, and i just want to export my jpg to the better possible quality.

thanks!

 

[Mark Sirota]

So you are saying that LR modify the jpg too much? is it bad ?

No, I'm not saying that at all. There are many JPEG compression algorithms. The one(s) that Lightroom uses are not as space-efficient as some others, but that doesn't mean they're worse. They might look better, for example. It's always a tradeoff.

... i just want to export my jpg to the better possible quality.

Then slide the Quality slider all the way to the right in the Export dialog, and don't constrain the dimensions. PPI has nothing to do with it. Nothing at all. Really.

 

[Replytoken]

I realize that I am reviving a slightly older thread, but I wanted to follow up on the theme of PPI settings. Most of the other browsing and editing programs that I am familiar with automatically derive a PPI figure, for example when printing and a paper size is given. What is LR's purpose of wanting to add this information to the file? And, what happens if I change the default from 24' to another number? I fully understand PPI and how it relates to printing, but I do not understand why LR wants to embed a specific number into the file? Any information would be greatly appreciated.

Thanks,

--Ken

 

[Victoria Bampton]

Lightroom would actually prefer not to add a ppi figure as it is fairly irrelevant unless you're running certain size related actions in PS, but not having it there would confuse even more people who don't understand it, and it does come into its own when you specify file size in inches or cm rather than pixels when outputting.

 

[Mark Sirota]

The file format provides a space for PPI metadata (that's all it is -- just metadata to possibly be interpreted by some program downstream). LR has to put something in there. There is no logical default value, so it asks the user.

The problem is that in the vast majority of situations the PPI value is irrelevant, because there is no downstream program that cares. So the user doesn't know what to put in there either...

 

[Bruce J]

I would take exception to Mark's reply. Actually, there are many downstream programs that use the PPI value. In combination with the pixel dimensions of the image, it is used to determine the default size (in inches or cm.) of the image. Many programs, including Photoshop, use that as the default size to display or print the image. If you open the Image Size dialog in Photoshop, that's the value used to calculate the image size.

I'm also concerned by a comment made by TanGu:
"i just want to export my jpg to the better possible quality". Importing a jpeg image into LR and then exporting it again as a jpeg is NOT going to give you a higher quality image than the original, no matter where you place the quality slider. At best it may equal the quality of the original, but I'm not even convinced that is true.

 

[Kiwigeoff]

I would take exception to Mark's reply. Actually, there are many downstream programs that use the PPI value. In combination with the pixel dimensions of the image, it is used to determine the default size (in inches or cm.) of the image. Many programs, including Photoshop, use that as the default size to display or print the image. If you open the Image Size dialog in Photoshop, that's the value used to calculate the image size.

I'm also concerned by a comment made by TanGu:
"i just want to export my jpg to the better possible quality". Importing a jpeg image into LR and then exporting it again as a jpeg is NOT going to give you a higher quality image than the original, no matter where you place the quality slider. At best it may equal the quality of the original, but I'm not even convinced that is true.

Bruce, the pint you make regarding Mark's reply has merit, of course the ppi in combination with the number of pixels determines the display/print area, however I believe that Mark was intending to mean that the ppi is not a rigid thing. I don't know for instance how many pppi the sensor in my camera is from whence it all flows, after which it is all calculations by software.
TanGu is not an English as first language person and I understand the meaning of "the better quality" to simply mean the best quality possible. Opening and resaving any jpeg image will lower the quality.
Thanks for your input and welcome to the forum.

 

[Mark Sirota]

I would take exception to Mark's reply. Actually, there are many downstream programs that use the PPI value. In combination with the pixel dimensions of the image, it is used to determine the default size (in inches or cm.) of the image. Many programs, including Photoshop, use that as the default size to display or print the image. If you open the Image Size dialog in Photoshop, that's the value used to calculate the image size.

I understand and agree with that, but I still maintain that the vast majority of images that are exported from Lightroom worldwide don't then go to Photoshop, nor do they go to anything else that cares what the PPI metadata field is set to. (And even if they do go into Photoshop, not everything you might do there cares.)

There will be exceptions, of course. But I still think that most people have no need to concern themselves with the PPI value.

 

[Bruce J]

Mark,

I think it's important for photographers to understand the relationships between PPI, image pixel size, and final image size. The reason I reacted to your statement is that I had just a few days earlier received a Christmas card from a relative w/ images that were clearly pixelated. I had seen some of the originals, which were fine and knew that they had been taken w/ an 8MP camera and not excessively cropped. In an effort to help and try to understand what had gone wrong, I asked how she had processed the images for her card. She showed me how she had printed the card (from Irfan View). The images came into Irfan w/ PPI set to 72. Because she did not know what that meant, she did not realize that when doing a minor cropping and resizing to a small image size for the card, the PPI would remain set to 72. OK for screen viewing, but completely inadequate for printing. This person has very little understanding of digital imaging; just wanted to make her own cards from some nice pictures she took. But, she got bit by an inappropriate (for her use) PPI setting.

 

[Replytoken]

The file format provides a space for PPI metadata (that's all it is -- just metadata to possibly be interpreted by some program downstream). LR has to put something in there. There is no logical default value, so it asks the user.

The problem is that in the vast majority of situations the PPI value is irrelevant, because there is no downstream program that cares. So the user doesn't know what to put in there either...

I agree with all of your posts, Mark, but for the life of me, I cannot understand why LR has to have PPI metadata at all, other than that is how the programmers wrote it up. We agree that it is not necessary for many programs (esp. non-Adobe programs). I wonder why we cannot just leave it blank? For example, an image file without the PPI metadata embedded can be read by Adobe programs, why can't LR export files without this data?

--Ken