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Exporting A Specific Size Without Forced DPI

When adjusting the exporting dimmensions of a photo, Aperature 3 allows you to also adjust the DPI.


But when adjusting the exporting size, say to 30 inches by 30 inches, will Aperture tell you what the DPI has gone down too? If you force the DPI this will lower the quality of the image. I don't want to force the DPI, but know what the DPI decreases too as I enlarge the photo. Does Aperature do this?


If not, how do I know what the DPI is as I increase the size and resample the image?


Thanks for your time.

Aperture 3, OS X Mavericks (10.9.2)

Posted on Apr 9, 2014 9:58 AM

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14 replies

Apr 9, 2014 10:20 AM in response to Blarespace

DPI is just a number that Aperture puts in the appropriate box when it creates a file when you export an Image. It is not calculated from any inputs (such as image pixel size), and it has no bearing at all on the Image being exported. It is sometimes used when rendering an image-format file, either to screen or to paper (i.e.: printing), but nowadays even then the user can almost always ignore it. (For printing it is useful to know the PPI (pixels per inch), but that can't be known until both the pixel dimensions of the file, and the target paper dimensions of the print, are known.)


Do you have a program/workflow that relies on the number in this data field? My recommendation is to simply ignore this data field (leave it set at something you can easily ignore, such as 75, or 300).

Apr 9, 2014 10:52 AM in response to Kirby Krieger

I don't think you understand what I'm asking. Let me explain.


The dpi greatly affects the quality of the image. 300 dpi is standard if you're taking your photo to a printer or print lab, so you can get a print, frame it and put it in a gallery. As the dpi decreases when you adjust the image, the quality of your print goes down.


Let's use the example above, and work with what Pixelmator tells me. The original photo right out of my camera is: 11 x 17 inches at 300 dpi. This is the image at it's maximum and optimal printing quality. Pixelmator also tells me that if I crop the image to a square and want to print/enlarge/increase the image to 30 x 30 inches, the dpi goes down too 115.5 dpi. I'm loosing pixels and data as I increase the printing size and the quality of the final print goes down. On the reverse, if I decrease the image size to say, 8 x 8 inches, the quality of the final print and the dpi goes up to 433 dpi. The average print lab only needs 300 dpi, but more the better.


I bought Aperature because I don't want to have to export an image from iPhoto, and then resize and resample it in Pixelmator, or any other third party program like Photoshop - I want to do all image editing and resizing in Aperture 3.


Does Aperature 3 resample the image dpi as I adjust the size like I'm talking about above? I need to know what the printing quality/dpi will be as I adjust the size. It must, becuase it's a professional image editing app. I'm just not sure of the setting or how to do this in Aperture 3.


Thanks for any help anyone can offer.

Apr 9, 2014 11:06 AM in response to Blarespace

Kirby's answer is perfect, but you have been talking at cross purposes.


The original photo right out of my camera is: 11 x 17 inches at 300 dpi.

It is very unusual to be thinking of physical dmensions when discussing digital images. A digital image has no physical dimensions, i.e. when coming right out of a camera. Then it just has a pixel size and can be rendered and displayed or printed with any size in inches on paper or on the display.


When you export from Aperture, you have the option to specify a destination size in inches plus dpi. And it will be up to you, to pick the combination you want. If you request "11 x 17 inches at 300 dpi", the pixelsize will remain the same, but any combination you want, will be possible. You can downsample the image or blow it up artificially. If you export by specifying a pixel size, you will have a much better control about the sampling, and that is preferable. And for this way of exporting Kirby's answer holds. When exporting by specifying a pixel size the dpi will just be a hint on how to display the image, but will have no effect on the pixel size of the exported image.

Apr 9, 2014 11:14 AM in response to Blarespace

The dpi greatly affects the quality of the image. 300 dpi is standard if you're taking your photo to a printer or print lab, so you can get a print, frame it and put it in a gallery. As the dpi decreases when you adjust the image, the quality of your print goes down.


For the benefit of other who may read this thread: none of this is true.


300dpi is not a "standard". It was never a standard, it was just a handy rule of thumb from 15 years ago based on the quality of the inkjet printers of the day. Both cameras and printing technology have improved massively since then. You can get excellent quality images at much lower dpi these days. AFAIK, Apple print products are rendered at 150 dpi, for instance. So, the quality of you print does not necessarily go down at lower dpi, it depends on the quality of the image.

Apr 9, 2014 11:34 AM in response to Blarespace

Pixelmator does its users a enormous disservice by conflating DPI -- a printer measurement that has virtually no use to anyone except printer engineers -- and PPI. Promulgating ignorance is inherently wrong.


They are very much not the same. A dot is not a pixel. Please note that many of the explanations turned up in that Google search themselves contain addition errors.


Nevertheless, read up on the difference, and then re-read my initial response.


Keep in mind that pixels contain no information about size, and that image-format files contain no useful information about size. Size of an image-format file is determined at the time of rendering the file. When rendered to a computer screen, the size is set by the OS. It can be controlled by the user, who typically does it once per display device, indirectly, and forgets about it.


When rendering images on paper (a/k/a "printing"), the size is set by the user. Until the size is set by the user, there can be no PPI because there are no inches. Importantly, you _are not_ printing fewer pixels or data ("I'm loosing pixels and data as I increase the printing size") when you print larger. You are spreading the same amount of information, and the same number of pixels, over a larger area. The information density decreases, and the resolution of the print decreases, but the number of pixels, and the amount of information they contain, stays the same. Resolution is a measurement of information density: information per unit area. You need to know the number of information units (pixels) and the area in which they will be rendered (inches, for example), in order to know the resolution of a print. Weirdly, perhaps, your image-format file actually has no resolution. The term cannot have meaning in that context. ("Megapixel" is a measurement of the amount of information, not its density.)


(NB: "Aperture", not "Aperature")

Apr 9, 2014 11:29 AM in response to Yer_Man

leonie, thanks for clarifing what Kirby was getting at. I guess I'm stuck on thinking in inches, since I'm an artist that displays sometimes in galleries, when I need to change my thinking from inches to pixels. I'll try some tests thinking in pixels and get back to you.


Terence Devlin, but as the dpi goes down so does the quality, no? If my orginal image is 11 x 17 inches at 300 dpi, and I increase the size to 48 x 72 inches the dpi goes down to 72 dpi. If I push the image further to 66 x 100 inches the dpi goes down to 55 dpi. This image will be very pixelated and look awful, no matter how sharp and clear your original image was. There's only so far you can push an image.


I recenly printed some images that started out as 11 x 17 inches at 300 dpi, and croped them and resized them to 30 x 30 inches, which brought the dpi to around 90 - 115 dpi, and the quality was not a good as if the dpi had stayed at 300 dpi. Isn't 72 dpi internet quality after all? You don't want to push a photo to go much under 100 dpi for printing, right? So staying as close to the 300 dpi I have still found is a good rule, which is what the commercial printers in my area tell me, whether it be a photo lab or a commercial paper printer that prints magazines.


But I guess all of my thinking is still in inches and dpi, when I should be thinking in pixels. But still, there's only so far you can push/enlarge an image.

Apr 9, 2014 11:48 AM in response to Blarespace

Ok, I need to change my language and terminology from DPI to PPI. And thanks Kirby for pointing out that I'm not loosing pixels as I increase the image, "

You are spreading the same amount of information, and the same number of pixels, over a larger area. The information density decreases, and the resolution of the print decreases, but the number of pixels, and the amount of information they contain, stays the same."


Eitherway though, if I make a preset in Apertur 3, to make my 30 x 30 inch photo to 300 dpi, when it's suppost to be at 115 dpi, it will look aweful if I force this new dpi on the image? I did a test and it looked awful. If you force the dpi, aren't you messing with the pixels?


Maybe this is a better question: Why does Aperture even give the user the adility to change the dpi from what it should be instead of resampling it? If you force the dpi or ppi to be higher than it should be, aren't you going to end up with a pixelated image that looks blurry, pushing the pixels further then they should go?

Apr 9, 2014 11:51 AM in response to Yer_Man

It is important -- crucial, in this thread -- to distinguish between Dots-per-inch and Pixels-per-inch.


300 dpi was standard many many many many moons ago. Then 1200, then, at 2400, ink-jet printers we able to produce high-quality prints.


Those are all dot-per-inch measurements. They refer to the actual dots of ink an ink-jet printer expels through any one of its nozzles. (Cleverly, engineers programmed the printers to overlap the dots. From then on, you could have a higher DPI than the number of "dot-diameters" that fit edge-to-edge in an inch.)


The current rule of thumb for image quality is Pixels-per-inch. 300 PPI will, on almost all printers seen by almost all people, produce images with imperceptible transitions between tones, and edges perceived as sharp. Someone skilled at printing can often get the same results from an image that starts at 150 PPI.


That's it for the rule of thumb. Actual results depend on the quality of the pixels, the handling of the file, the program(s) used, the quality of the printer, the quality of the paper, the weather, and the acuity of the viewer, among other variables.

Apr 9, 2014 12:03 PM in response to Kirby Krieger

Thanks Kirby for all the info.


So to wrap up my specific question about printing, dpi, ppi and resolution, when exporting an image . . . When I export an image from Aperture 3, I simply export my final edited image using the Export>Original or Export>Version>Jpeg - Original Size. This will give me my edited photo at the maximum pixels???


For my cropped square image, the above preset gave me an image of 3277 x 3277 pixels, with the default resolution of 72 pixel/inch, which in inches is 45.514 x 45.514 inches at 72 pixel/inch.


So all I need to do for printing, is to send this 3277 x 3277 pixel file to the printer, and then specify with the printer that I want it printed at 30 x 30 inches, not concerning myself with resampling it or adjusting the resolution?


Does that sound about right?

Apr 9, 2014 12:11 PM in response to Blarespace

Now we're getting somewhere 🙂 .

Blarespace wrote:


Maybe this is a better question: Why does Aperture even give the user the adility to change the dpi

There was a time when some programs used this when they rendered images on-screen. Afaik, this is no longer needed. Imho, Apple should remove it from Aperture. The cost of being incompatible with deprecated programs does not out-weigh the cost of confusing current users.

if I make a preset in Apertur 3, to make my 30 x 30 inch photo to 300 dpi

Suggestion: specify pixels in your Image Export Presets. (Don't use either "Fit within (Inches)" or "Fit within (Centimeters)".) Export at original size (that's all the pixels in the Image) unless you have a need for a smaller file (e.g.: post on the Web). For printing, you never want to through away any information. Worry about the size of the image only when you print. Then, do the arithmetic to determine if your image size (in pixels) can be satisfactorily printed at the size you want (inches) by dividing the number of pixels in one orthogonal direction (e.g. "length") by the number of proposed print inches in the same direction. The result is your print resolution. You can use the rule-of-thumb mentioned elsewhere in this thread to guide your decision on whether this might produce satisfactory prints, or not.

Apr 9, 2014 12:35 PM in response to Kirby Krieger

It is important -- crucial, in this thread -- to distinguish between Dots-per-inch and Pixels-per-inch.

and lines-per-inch, when speaking of the visual resolution of a photo. 😉


I agree with your summary Kirby, and that is how I am accustomed to using these terms in my image processing lectures. Only, when referring to the "Export" settings of Aperture, we are having the problem, that the export setting parameter is called "dpi". Aperture's export setting parameter "dpi" is used for all purposes like pixels-per-inch.


When referring to the export settings, I'll continue to call it "dpi" - that is the parameter to be set, when exporting, and that are the metadata tags added to the exported image file.

User uploaded file

Apr 9, 2014 1:22 PM in response to Blarespace

Terence Devlin, but as the dpi goes down so does the quality, no? If my orginal image is 11 x 17 inches at 300 dpi, and I increase the size to 48 x 72 inches the dpi goes down to 72 dpi. If I push the image further to 66 x 100 inches the dpi goes down to 55 dpi. This image will be very pixelated and look awful, no matter how sharp and clear your original image was. There's only so far you can push an image.


Again, not necessarily. The quality of the image as you reduce the dpi will depend on the sharpeness of the image and the quality of the printer. 72 dpi from an Inkjet will be a very different thing from 72 dpi on a more sophisticated devices.


The point I'm making is that there is no "standard" and that the rule of thumb you quoted is from another time. It may still work, but there are other possibilities...

Exporting A Specific Size Without Forced DPI

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