Lightroom Image size

[MikeMcMahan]

Just started working with Lightroom 3 and RAW files, but the question applies to all file types. Basic question is "What is the native resolution of an imported file in PPI?" or asked another way. "What is the physical dimension of my imported image, since I know the pixel deminsions?" I had a light version of Photoshop many years ago that came with my first digital camera and it gave me the phyical size of the image and an easy option to resize the image, based on PPI. I could even put rulers on the image. But in Lightroom the only place to resize the photo is during export or print. I understand pixels per inch and dots per inch determines resolution, but I don't know what the PPI is on my image to begin with. Also, I can expand the image to 1:1 on the screen, but what is the real physical size? Very confused here.
Mike

[corvus2606]

you dont change the size of the image in lightroom, It only gives you that info on export because that is where it should be done.

LR is non-destructive, meaning that nothing permanent is done to the original file. the ppi settings on a straight out of camera jpeg will be whatever the camera outputs at, but RAW isnt a format that uses PPI, that is done when you export.

[MikeMcMahan]

Thanks, did not understand tha RAW does not use PPI. Basic reason for my question is that my daughter wants me shot an image for my grandson's room that will be 36" x 54". I have a 10 megapixal camera and I realize that this is on the edge of or below the resolution required for that size of an image. I appears that I can only tell if the resolution is good enough by eye ball when expanding it to say 4:1. I have tried to find the native PPI of my camera for JPEG but cannot determine it in the users guide. Might have to go to Sony directly and ask the question.
Mike

[vsa]

If my tests are correct then from a 10mp (3648x2736) image printed at that size would be around 67ppi.. which isn't all that great. Might want to print at a smaller size as the 54" x 36" is pretty massive.

Where would you put the picture?

[MikeMcMahan]

Thanks for that response. How did you calculate that DPI? The poster is for a bedroom for a 3 year old boy. I agree, it is a tad large and I had doubts about my camera being able to handle it, but wanted to try. Just going through the exercise has been beneficial to me.
Thanks, Mike

[MikeMcMahan]

Hey, never mind that last post. I know how to calculate PPI, but I was thinking DPI when I read it. Which leads to the question: What is the relationship between PPI and DPI? They both have the same principles, but one applies to the computer image, and the other applies to the printer. We have to judge the final printed image based on the computer image we are processing and I guess it is a learned judgement that only comes with experience.
Let me know what you think.
Mike

[vsa]

Why don't you enlarge the picture to desired dimensions, then crop it to fit normal size paper that you can print out and see how it looks?

[MikeMcMahan]

I did think of that and will probably try that route once I get the final image that I really want to expand. I was trying to figure it out on the computer before spending money on experiments, but you only learn by trying things.
Thanks, Mike

[MikeMcMahan]

Originally Posted by corvus2606

you dont change the size of the image in lightroom, It only gives you that info on export because that is where it should be done.

LR is non-destructive, meaning that nothing permanent is done to the original file. the ppi settings on a straight out of camera jpeg will be whatever the camera outputs at, but RAW isnt a format that uses PPI, that is done when you export.

I understand this, but to help me grasp what happens in RAW to the pixels, let me ask you a follow-up question: In Loupe view, I assume that Lightroom picks the number of PPI that fits my monitor for the Fit or Fill viewing option. But what is Lightroom doing when I go to 1:1 or any of the zoom ratios? I assume 1:1 is actual image size, but what is that size if Lightroom does not use PPI in RAW? On the preview in the Navigator panel to the left, the 1:1 image box only covers 1/9th of the image in the center of the image. The image is 3872 x 2592 pixels. Lightroom must be using some sort of algorithim to determine what to display when selecting the viewing zooms.
I hope you understand my confusion.
Mike

[kevnsmth]

I'm certainly no expert on these matters, but it seems to me there is a lot of confusion around this topic. Here's an interesting test. Select any image in your library and note the resolution. Now export the image at full resolution at a number of different PPIs. Notice that every exported JPG has the same resolution and file size. Embedding PPI information is simply a way to tell applications the approximate size in inches of the image. This embedded PPI doesn't actually affect the resolution or quality of the JPGs however. After you've printed a JPG, you can then state the actual PPI of that print based on the physical dimensions of the print, but the PPI embedded in the JPG file doesn't affect the quality of the print (unless the lab's printing software is looking at this embedded PPI and doing some scaling to make the print, and I wouldn't expect this).

To the OP's last question, when viewing an image at 1:1, Lightroom is simply displaying the image at full resolution. PPI is not being considered in this case, nor is it involved when displaying at Fit or Fill.

If anyone has more knowledge, please feel free to correct me.