Why can't I export greater than 72 dpi?

Are you sure the preset you are using when you export the version is the preset you created with the 300dpi setting?

if you go into the preset setup window and create a new preset or modify an existing one that preset isn't automatically selected when you return to the export dialog. You need to select the preset you changed.

If your image is 10.4 MB and 5184 x 3456 in size, why would you need to change anything? That seems to be large enough to be able to print at just about any size and get a good clean image print. How large of a print are you looking for?

Also, can someone on this thread shed some light on the difference between the exported image DPI and the print DPI? I'm a bit confused as to what the exported image DPI is and what affect it has on the exported image.

Thanks,

Mac

DPI means nothing on a computer. There are no "inches" to have a "dots per..." Apple apps tend to work at 72 dpi as that's what most screens are. However, an image at 1 dpi is identical on screen as one as 300 dpi.

DPI only comes into play when you go to print. At that point what matters is the total number of pixels you have. So, in the case you describe

5184 x 3456 you have a total of 17915904 pixels.

DPI decides how densely you spread them on the paper:

At 300 dpi you'll get an image that's 5194/300 = 17.31 inches.

At 150 dpi you'll get an image that's 5194/150 = 34.62 inches

And at 600 dpi - well you can do the math yourself 😉

So, whether you export at 300 dpi or 72 dpi or 1 dpi doesn't matter. It's only when you print and desire the dimensions you want to print at.


Regards

TD

TD,

Why does Aperture include the ability to change the DPI in the export settings at all? I completely understand the part about the overall pixel dimensions and how DPI plays a roll on the print side of things, but what is the DPI on the export side of things all about? As you mentioned, it means nothing on a computer.

Your explanation doesn't really answer the question. Is there any point in changing the DPI in the export settings? It sounds like you are saying no, but then why is the ability to do so included? What purpose does it serve?

As for setting the DPI on the print side of things, I am assuming this only comes into play if you are printing from home, or using Photoshop? I send my images to a print lab, so setting the DPI never comes into play. The only time I seem to be able to interact with DPI is in the export settings in Aperture, but from what it sounds like, that isn't really doing much.

Can you be a little more specific?

Thanks,

Mac

TD,

Any thoughts on why the DPI is included in the export settings? If it has not affect on anything useful, why is it there? I'm curious because before I start exporting images for upload to other sites where I might purchase prints, I'd like to know what this DPI is and what it should be set at.

Thanks for your time and help.

Mac

It's about the quality of the output file. Obviously, a 300 dpi file will have a lot more pixels than a 72 dpi one - and that brings us back to the post above. So the question is, "What's this file for?" . If it's for screen use you can keep the files size small and export at a low dpi. If it's for printing, then you increase the dpi and have a larger file.

It's broadly analogous to the export dialogue in iPhoto where you can choose the export quality as small/medium/large

Regards

TD

Terence Devlin wrote:
DPI means nothing on a computer. There are no "inches" to have a "dots per..." Apple apps tend to work at 72 dpi as that's what most screens are.

It's been many years since Apple sold a 72dpi monitor. They're all well above that now, especially the Retina Display. Windows advanced past 72dpi before the Mac did, assuming 96dpi.

The dpi doesn't matter for screen display, but it does matter if you import it into a print layout app that needs to assume a size for print. If a 2400x3000 JPEG has 300dpi encoded into it, it will drop in on the layout at 8x10 inches. If it had 72dpi encoded into it, it would drop in at many times larger than the page. This print scenario is the only one where dpi really matters. If the original poster is going for print, this is problem worth solving. If the image is only for the screen, it should be exported at the proper pixel height and width (e.g. 400x600px) and the dpi doesn't matter.

Terence Devlin wrote:
It's about the quality of the output file. Obviously, a 300 dpi file will have a lot more pixels than a 72 dpi one - and that brings us back to the post above. So the question is, "What's this file for?" . If it's for screen use you can keep the files size small and export at a low dpi. If it's for printing, then you increase the dpi and have a larger file.

You also wrote:
"DPI decides how densely you spread them on the paper:

At 300 dpi you'll get an image that's 5194/300 = 17.31 inches.

At 150 dpi you'll get an image that's 5194/150 = 34.62 inches"

Isn't your comment above saying just the opposite though? At 300 dpi in your example you are getting a smaller (in inches) image.

Anyway, isn't setting this dpi just artificially changing the pixels? I mean, it really shouldn't have any effect on the print quality of the final product.

It's broadly analogous to the export dialogue in iPhoto where you can choose the export quality as small/medium/large

TD, again forgive me for possibly misunderstanding you, but wouldn't your above statement relate more to the image size rather than the DPI number you choose? You can export images at JPEG Original size, so why would the export DPI have any affect on the exported JPEG at original size. The size is the size. Any DPI manipulation at this point would (and should) be artificial. This is why I am still confused as to why Aperture includes this option. The export options in Aperture (and I am assuming iPhoto to a lesser degree) are pretty clear when it comes to exporting and size. you can export at original, half, a percentage of your choosing, a different pixel dimension, small, medium, large, etc, etc. In none of those cases do I undersand why DPI would need to be altered. Altering it does nothing to the image size, at least so far as I can tell.


Mac

Message was edited by: macorin

Message was edited by: macorin

macorin wrote:
Anyway, isn't setting this dpi just artificially changing the pixels? I mean, it really shouldn't have any effect on the print quality of the final product.

The answer is "yes" or "no" depending on whether resampling has been done. If no resampling, then there is no artificial change, only a change in density with change in size as a side effect. If it is resampled, then yes the image has been changed.

Most discussions of this completely bypass the resampling issue and that's why people argue so much. They are both telling the truth but the incomplete context makes them think they're arguing.

I'm not even sure what resampling is. Can you even do resampling with Aperture without using an external image editor like Photoshop? I don't typically do that, so I doubt changing the DPI would have any effect on my exported images. Still, I'm trying to learn what all this stuff means.

What is resampling and how does it relate to all of this?

Mac

Resampling means adding pixels to the photo. Again, as I said above, what matters is the total number of pixels in the photo. Resampling is an attempt to interpolate or add pixels above that amount. While it adds pixels unless you're very lucky it ill degrade the quality of the actual image.

Regards

TD

TD,

Thanks for continuing the discussion. I don't plan to add any pixels, so I am just going to leave the dpi alone. That said, is 72 somehow the baseline number that won't add pixels? It seems rather odd and kind of random.

Mac

Mac and those of you unsure of DPI and how it relates to the screen and print, have a look through of this great visual explanation of DPI and Resolution. This "article" by JOHN HENSHALL has to be one of the best, lots of pics for us visually oriented people.

http://www.epi-centre.com/basics/index.html

Let us know if this helps.

Tony

Tony,

Thanks for the link. I certainly did find it interesting and it is extremely well described by the author. Still, as you mentioned, it does mainly relate to screen size and still leaves me a bit confused as to whether or not to play around with the dpi upon export of versions. To this point, I have basically just left it alone and for the most part this has been okay. Every image I've ever exported and uploaded to shutterfly, kodak, snapfish, etc has been okay to print at sizes up to 20x30. I rarely print at that size, so if I am okay at that size, I am obviously fine with less than that.

I still like to understand all facets of what I am doing though, so it bothers me that I don't understand what changing that dpi value would do. To the best of my understanding, by exporting at 72 dpi, I am at least guaranteeing that it will look good on any computer screen at its original size. As for printing purposes, the overall size of the image in pixels seems to be large enough to be able to print at my desired sizes without degradation or "pixelation" so it seems that I really needn't worry myself with it all too much. I suppose it I wanted to print one of my images in a giant billboard size, I could adjust the dpi, which in turn would add more pixels, which in turn would allow me to blow up the image even more.

Again, this is my best guess as to what is going on and how to handle it.

Mac

Message was edited by: macorin

Message was edited by: macorin

What version of Aperture and OSX are you using?

Ernie