# Exporting:  pixels per inch / cm?



## hp5rebec (May 13, 2009)

Hello,

Plebe here.

I shoot with a Nikon D-8' in RAW format.  When I export images, they default to 24' pixels per inch.  Is this sufficient?  I guess what I want to know is:

(1)  Does this default to 24' regardless of image size?  Is this a function of image size, or does it vary but is not related to image size at all?
(2)  When is it good to modify this?  I'm assuming that if I'm exporting to print a smaller image, I might not need that level of detail.
(3)  Does it ever make sense to increase this?

I never know what to do with this field.

Thanks!!


----------



## Denis Pagé (May 13, 2009)

Welcome to Lightroom Forums Plebe!

Until you go to paper, it is all meaningless and can take any value so, (1) is your closest answer and "not related to image size at all". This is no more than a declared value that can be changed later without altering file size or resolution. What is giving you the resolution is the number of pixels you can get. Screens know nothing about inches and just care about the number of pixels so for them, pixels _per inches_ make no sense.


----------



## hp5rebec (May 13, 2009)

If I'm exporting to a JPEG (from a RAW), however, can't I reduce the pixels per inch, even though I'm not printing it?  Seems to me it's just a way to modify the resolution.  This is similar to my scanner, which asks me what dpi (essentially pixels per inch) resolution I want.

Also, if it's meaningless at that point, why is this field editable?  LR should just grey the field out.

Basically, I want to export it with the most amount of detail as possible.  I'm guessing that I cannot increase the pixels per inch ever, but in some circumstances I may want to reduce the pixels per inch.  

Thanks for the response, BTW.


----------



## Replytoken (May 13, 2009)

hp5rebec;443'9 said:
			
		

> If I'm exporting to a JPEG (from a RAW), however, can't I reduce the pixels per inch, even though I'm not printing it? Seems to me it's just a way to modify the resolution. This is similar to my scanner, which asks me what dpi (essentially pixels per inch) resolution I want.
> 
> Also, if it's meaningless at that point, why is this field editable? LR should just grey the field out.
> 
> ...


 
To briefly answer your comments.

1 - The box does not modify the file's resolution.  It is only an "advisory instruction" (metadata) that some software might read.

2 - Many of us would love to see this field grayed out, or removed all together!  But, it is there for programs that will use the metadata when they read the exported file.

3 - You are correct on both accounts.

My advise would be to just ignore the field.

--Ken


----------



## Brad Snyder (May 14, 2009)

hp5rebec;443'9 said:
			
		

> Also, if it's meaningless at that point, why is this field editable?  LR should just grey the field out.



Perhaps it's an Lr urban legend, but we're told by old timers that this field is editable in order to allow photogs to please down stream users; clients, art directors, etc. whose only knowledge of resolution is that is should be some optimum number of pixels per whatever.  There was a clamor to make it 'settable', even though it has no meaning in this context.


----------



## Denis Pagé (May 14, 2009)

hp5rebec;443'9 said:
			
		

> If I'm exporting to a JPEG (from a RAW), however, can't I reduce the pixels per inch, even though I'm not printing it? Seems to me it's just a way to modify the resolution. This is similar to my scanner, which asks me what dpi (essentially pixels per inch) resolution I want.


No. It just tell to use that much of paper for that many available pixels. This value can be changed anytime without affecting resolution. Take an image of 2''' x 3''' pixels and make it 1ppi then print... :shock: really want to spend 64428 8½" x 11" sheets? Now make it 3''ppi and you need just one sheet (6.6" x 1'"). But in any case, you still have 3''' x 2''' pixels!

Scanning is a completely different context as the scanner does manipulate physical things having measurable dimensions. A paper having a mesurable width by a mesurable height, an object you can take with your hand to put on its surface, a film slide X_mm_ x Y_mm_ etc.

In this case, the question is this: "For each given length of the scanned medium, how many pixels do you want?".


----------



## Mark Sirota (May 15, 2009)

Brad Snyder said:


> Perhaps it's an Lr urban legend, but we're told by old timers that this field is editable in order to allow photogs to please down stream users; clients, art directors, etc. whose only knowledge of resolution is that is should be some optimum number of pixels per whatever.  There was a clamor to make it 'settable', even though it has no meaning in this context.



I think that's right.

I think it's also there because LR has to write _something_ in that metadata field, and rather than just make something up they're asking the user.


----------

