Lightroom export ppi

Cocohoney

Cocohoney

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Name
Alexandra
Edit My Images
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Hi, I have Lightroom 3 and I am confused about exporting the files once I have edited them.

When I export them it wants me to specify a ppi. I understand 300 is the standard, but as I don't really understand how ppi adjustment (?) works I don't know if this is right for all my files.

When I crop an image in photoshop if I specify 300ppi and then zoom right in (ok, I am going big here) I can see pixels. If I crop the same picture to the same size without specifying a ppi and zoom in to the same level, the image is still as smooth as it was pre crop.

So this worries me with specifying a ppi in Lightroom.

Please feel free to state the obvious to me- technology is a steeeeep learning curve for me!
 
ppi is just a hint to the print process on how big to print something. If you have an image 3000 pixels on the longest side and print at 300ppi, it will be 10" long. If you print at 150ppi, it will be 20" long.

What you should be concentrating on is what you are outputting the image for. If it's for display on the web, ppi doesn't matter.
 
Ok, thanks. So if I crop to 5x7 and state 300 ppi does it mean that if I then print it at 15x21 the ppi will be 100?
 
No. When you crop to 5x7 in LR, you are cropping to a 5x7 RATIO. That could be 5x7 pixels or it could be 5000x7000 pixels (or any 5x7 multiple in between). The time it matters is when you EXPORT the images. It depends what you set the resize option to if it is measured in inches or pixels and then how many ppi it stores in the file.
 
Ok, I haven't been resizing when I export, does that matter? Is 300 ppi "full resolution" then?
Why am I getting the comparative pixelation when I look at it zoomed right in photoshop?

I have read those threads now thanks- I'm afraid I still don't really understand...I guess so long as 300ppi is the right resolution to put in the box when I export then I just have to accept it, I don't think I can get my head around it.
So if my pictures are usually 5x7 and I want to print bigger but the same ratio, should I be resizing or just leaving it? And would it cope with being printed big, or do I need to do something else for that?
Thanks for the help
 
OK I can understand why you are getting confused over this PPI thing.

Putting a number into the PPI field simply fills in a data entry into the files data set. This can then be read by other software in order to extrapolate the dimensions of the file using that setting. Designers find it useful to ascertain if a image file will produce a image of the appropriate size for the project they are working on. It has no effect on the final size of the file.

Try exporting a file at 300 PPI and another at 600PPI the file size stays the same no more pixels are added or taken away. Photoshop will report one as being smaller than another, but that's simply because it's being told to divide one set of dimensions by 300 and the other set by 600.

What is concerning is what you are seeing when zoomed in. This pixalation effect could be a number of things and without seeing it it's difficult to determine. They could be JPEG artifacts, caused by excessive compression. Try exporting as TIFF's with no compression or anything done to them. Are you still seeing pixalation. It could also be over sharpening. Import an image into Lightroom and apart for any small adjustments to exposure, export it right out again using the default setting. Do you still see pixalation?
 
Thanks Chappers, that actually makes sense to my inadequate brain.

I will try what you suggest, but the image I noticed this with was RAW and edited entirely in Photoshop, not exported there from Lightroom. I cropped a picture using the photoshop tool and didn't realise 300 was entered in the box to specify ppi. When I zoomed back in (very close, was looking at tiny skin differences) I thought it was odd as there was pixelation.
So, I undid my crop as that was the only thing that had changed and checked again- no pixelation. I went through the crop procedure and noticed the value in the ppi box, so tried deleting this and cropping and zooming again- this time it was ok, no difference to the pre crop. I tested another image and the same thing happened, and that was before any editing at all apart from the usual 20 sharpen when you open the RAW file.
This is why I got all het up about specifying a ppi! Can you think of anything that could explain it?
 
Try exporting a file at 300 PPI and another at 600PPI the file size stays the same no more pixels are added or taken away. Photoshop will report one as being smaller than another, but that's simply because it's being told to divide one set of dimensions by 300 and the other set by 600.
Click to expand...

WRONG the 600ppi will be 4 times as big

Mike
 
Hi Mike- what ppi should I export my files from Lightroom at then?
Is there a way of converting the RAW images I have edited in Lightroom into jpegs without specifying ppi?
 
mike weeks said:
WRONG the 600ppi will be 4 times as big
Click to expand...
That depends if you're exporting in PIXELS and setting the PPI or exporting in INCHES and setting the PPI. Two totally different results.

Think of the physics involved and it's all plain sailing ;)
 
If all else is equal and you change the ppi there will be a file size difference and the question was asked for print size setting in inches.

Alexandra as long as you dont select the resize to fit you will have no resizing. I normally export at full size if using for an album and then resize as required.

Mike
 
:runaway: nope, you've all lost me

I never did like physics ;)

So, if I'm not specifying a size, and am only putting the pixels/inch in the export box, it's fine at 300 ppi?
 
Ok, cross post, I get that then I think- you don't just crop for sizing then?
 
Setting the 'ppi' when saving an image merely puts a number in a file, which may tell a printer what size to print the image. It has no bearing on the stored image as such.

When you want to print a copy of the image the printer needs to know how big to print it. There are several ways of doing this, one being to tell it directly "I want this print to be 6x4". If 6x4 isn't the same aspect ratio (shape) as your image the print will be tall and thin or short and fat to some degree. Another way of telling the printer how big to print your image is to tell it how many pixels of the image to make one inch on the print. You can either enter the number directly in the printer's control panel at printout time, or the printer driver might look for the number in the image file. If it can't find one, or the printer driver doesn't have that feature, it will probably use a default number, often 300 pixels per inch (ppi).

Many commercial online printers use the same range of printers, which will only print at 300 ppi. It doesn't matter what number you may have specified when you saved the file, the printer will ignore it and print at 300 ppi. So my Nikon D70, which produces pictures at 3000x2000 (give or take a few) pixels will yield prints of 3000/300 = 10" on the long side and 2000/300 = 6.7" on the short side.

The short answer is the ppi setting saved with the image will have no effect on the stored image, nor how it appears on the screen. It might affect the size of any prints made from the image.
 
Stratman said:
Setting the 'ppi' when saving an image merely puts a number in a file, which may tell a printer what size to print the image. It has no bearing on the stored image as such.
Click to expand...
This isn't quite true....

In Lightroom, when you export, you have the option of resizing the output image. In the dimensions tab, you can choose to resize to pixels or inches or centimetres. If you resize to pixels, Lightroom stores the ppi/ppcm value in the file as a hint to the print process as to how big to print the reultant image.

If you specify inches or centimetres for the resize, LR will use the ppi/ppcm to work out how many pixels to make the image. It will also store the ppi/ppcm value in the file, which can be overridden at any point in the future, but the file will have been sized directly from the ppi/ppcm value.
 
Stratman said:
The short answer is the ppi setting saved with the image will have no effect on the stored image, nor how it appears on the screen. It might affect the size of any prints made from the image.
Click to expand...

Export a photo from Lightroom at 640px longest side, 300 ppi. Now export the same image except at 72ppi.

Embed both in the same word doc, PDF or email (if using http mail). Spot the difference?

PPI can make a difference, just not always in the way that you think it might!
 
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:bonk:

Guys...you are not helping :D

I think you are saying that the actual amount of pixels in the picture cannot be changed unless I resize simultaneously?

As in- if I say 6x4 and 300ppi, then the image will contain 7200 pixels.
If I print at 12x8 then it will contain errr, ummm, well, more pixels than 7200.

What do you lot do if you have images you may want to print to a decent size to put on the wall. They have been uploaded to Lightroom as RAW files, and edited in there. What do you do next...?
 
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Cocohoney said:
:bonk:

Guys...you are not helping :D

I think you are saying that the actual amount of pixels in the picture cannot be changed unless I resize simultaneously?

As in- if I say 6x4 and 300ppi, then the image will contain 7200 pixels.
Click to expand...
Nope, it will be an image that is 1800x1200 or 2.16Million pixels.

Cocohoney said:
What do you lot do if you have images you may want to print to a decent size to put on the wall. They have been uploaded to Lightroom as RAW files, and edited in there. What do you do next...?
Click to expand...
I would crop to the right aspect ratio, find out what dpi my print lab uses (I use DSCL which is 300ppi) and then I would export so that the long size is the right number of pixels. So, for example, say I'm printing an 18"x12" print at 300ppi, I want the longest side to be 18 x 300 = 5400 pixels. In the LR export, I will make the image 5400 pixels on the longest side and then upload that to DSCL.

You can also convert the longest side to be 18 inches at 300ppi in the export. That should give you an image which is 5400 pixels on the long side.
 
Cocohoney said:
:bonk:

Guys...you are not helping :D

I think you are saying that the actual amount of pixels in the picture cannot be changed unless I resize simultaneously?

As in- if I say 6x4 and 300ppi, then the image will contain 7200 pixels.
If I print at 12x8 then it will contain errr, ummm, well, more pixels than 7200.
Click to expand...

No, you will have the same amount of pixels. You could go back to lightroom and do another export at the new size.
What do you lot do if you have images you may want to print to a decent size to put on the wall. They have been uploaded to Lightroom as RAW files, and edited in there. What do you do next...?
Click to expand...

The beauty of Lightroom is that you can go back as often as you want and create new sized versions as required.

Mike
 
Cocohoney said:
What do you lot do if you have images you may want to print to a decent size to put on the wall. They have been uploaded to Lightroom as RAW files, and edited in there. What do you do next...?
Click to expand...

Whenever I export any files from Lightroom I go through the following steps:
Check aspect ratio of output media, crop if needed and create a snapshot of that crop in the develop module.
Find out required file type (usually jpeg)
Find out how big the image needs to be, for screen viewing this is usually expressed in pixels, which is easy. If the image is going to get printed you need to know the size it will be printed at and the printers ppi (mostly 300) and then input these into the export dialogue. From the size and resolution (ppi) Lightroom will know how many pixels are needed.
I then choose a sharpening setting relevant to the output media and apply a colour profile if requested by the printer (if not sRGB is fine).

This way every picture I export has been resized with the exact number of pixels that are needed and I am able to check the image at 100% outside of Lightroom before I send it on. If I'm sending an image to be printed I know exactly what is going into the printer, so can get consistent results.
 
Thanks all of you.

Do any of you put photos on discs for other people, so you wouldn't know what size they would want to print at?
I have some pictures for a friend, I know she will want to print at various sizes.

Is it ok not to put a size when I export them and just put 300ppi?

They are all 6x4 at the moment.
 
I used to, but don't these days as I prefer to handle my own prints to keep quality known.

With Lightroom export presets it's easy to have a folder for 6x4, 12x8, 24x16 and the all important watermarked Facebook ones.
 
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