Export from Aperture at 300 dpi changes to 72 ppi in Photoshop

I have exactly this 72 ppi problem with my iPhone SE. And if I go to File > Export, I see no 'Export Preset'. What I see is this:

So how and where can I set the resolution to 300 ppi?

Thanks in anticipation of advice.

Thank you, too, léonie, for your explanation. I realize that I am posting in the wrong part of these discussions since I am not exporting from Aperture but from the Mac's Photo app, but as I am at the present at the stage of trying to find out what is going on before I try to modify the behaviour of the Photo app, the principles are the same. Perhaps I ought to confess that I am not a total ignoramus, though very much an inexperienced amateur as far as printing digital photos is concerned, since I was an electronic engineer once, and then a lecturer in maths and physics, before abandoning all that for a career in music.

I downloaded photos from my iPhone to Photos on the Mac, then exported them as JPEGs and, later, as TIFFs. I then opened one of the TIFFs in Photoshop CS6, and I attach what is shown under 'Image Size'.

If I multiply 3024 and 4032, I obtain approximately 12.2 Mp as the total number of pixels, which corresponds very satisfyingly with the specifications of my phone's camera. ('Pixel Dimensions 69.8 M' presumably refers to the actual size of the pixels.) But if I multiply 42" x 56" x 72 ppi, which, as far as I can see, should yield the same answer, I obtain a mere 169,344 pixels.

At this stage I have two questions.

Firstly, why this discrepancy between 12.2 Mp and 169,344 p?

And secondly, will I get sharper prints if I type 250 or 300 in place of 72 into the 'Resolution' box?

Thank you in anticipation for answers from you or from anyone else.

This is the forum for Aperture, that's the export dialogue for Photos.app, an entirely different application. As it is a freebie and a consumer app, it does not have the same options.

Then... are you sure it matters? DPI means absolutely nothing unless you're printing.

There are no "inches" to have "dots per..." Size is measured in pixels. That's the same on your camera. It doesn't take 10 x 8 or 6 x 4 shots. It takes shots measured in megapixels. For instance 4,000 x 3,000 is a 12 megapixel camera.

Using that example, that shot from that camera has 12 million pixels. So that's how many "Dots" there are. To decide the ratio of dots per inch, you now need to decide the "inches" part. And that's printing. Print at 10 x 8 and the dpi will be 4,000/10 or about 400 dpi. At 6 x 4 then it's 4,000/6 or 660 dpi. Work the other way: Print at 300 dpi and the resulting image will be about 13 inches on the longer side.

So, your photo as a fixed number of pixels. Changing the dimensions of the print will vary the dpi, changing the dpi will vary the dimensions of the print.

For more see http://www.rideau-info.com/photos/mythdpi.html

Regards

TD

Thank you, Terence Devlin; and I understand your arithmetical exposition. Moreover, the link in your answer leads to a very useful article. The fact is, though, that if I visually compare the definition of an image on my phone to that of the same image when exported to my Mac, the latter is worse. Have you any idea why this might be so?

I also observe that when I open an image exported from my phone in Photoshop, Image Size shows the resolution as 72 ppi, whereas if I open an image made with my Canon camera in Photoshop, resolution is shown as 300 ppi. Does this not mean that the latter image is sharper when viewed or printed at the same size as the former?

I also observe that when I open an image exported from my phone in Photoshop, Image Size shows the resolution as 72 ppi, whereas if I open an image made with my Canon camera in Photoshop, resolution is shown as 300 ppi. Does this not mean that the latter image is sharper when viewed or printed at the same size as the former?

The 72 DPI or 300 ppi are just a hint when printing. it depends on the application you are using, if this recommendation can be overridden. Printing at 72dpi will be less sharp than printing 300 dpi, but your photos will not have lost any resolution , if the pixel size is still the same. My Canon photos are still exported with the correct dpi settings.

If 'Printing at 72dpi will be less sharp than printing 300 dpi' and 'your photos will not have lost any resolution' are not mutually contradictory, Léonie, then photos will have ceased to be pictures to delight the eye and have become nothing but electronic configurations of I-s and O-s, describable in arithmetical terms by means of a reassignment of meaning to the old, once visually-meaningful word 'resolution'. I am concerned with how photos look.

I am concerned with how photos look

As are we all. The point is that there are many variables that may account for the difference between what you see on your phone screen and what you see on your Mac or when you print.

In the case of the phone and the Mac, the obvious one is the quality of the screen and backlighting thereon. Pixel density on a phone is up to twice that on a Mac. (Models very but see this: https://www.tekrevue.com/retina-display-comparison/ for example.) Photos that look great on my iMac look lifeless and flat on my HD TV. Again, screen quality is the issue - the combination of image, pixel density and backlighting. And let's not even get into the thorny issue of colour matching and the different profiles. My MacBookPro has about 25 different colour profiles I can choose, but which one does my camera use? Did it get converted when I open it in Photoshop or some other app? Photoshop is a very powerful and complex app with many different settings that are opaque to the unwary consumer user.

When it comes to printing the old rule-of-thumb was to not go below 300dpi for best quality. However, printing technology has changed and improved, and 150dpi from an inkjet printer is a lot different from 150dpi on a laser printer, so direct comparisons are impossible. Then add in issues of paper quality, clean v dirty print heads, and again, colour matching, and you realise that the screen stuff was easy!

What does this tell you? This is all perceptual, all about how the photo looks. Everything said here is only about the device(s), we've not even mentioned the quality of the image...

So, the specific reason why an image on your phone may look better than on your Mac? Better screen, and by luck, better colour management. But that's a guess...

If 'Printing at 72dpi will be less sharp than printing 300 dpi' and 'your photos will not have lost any resolution' are not mutually contradictory, Léonie, then photos will have ceased to be pictures to delight the eye and have become nothing but electronic configurations of I-s and O-s, describable in arithmetical terms by means of a reassignment of meaning to the old, once visually-meaningful word 'resolution'. I am concerned with how photos look.

Agreed.

But is not contradictory.

The (possible) geometric resolution of a digital photo is as good as the pixel size of the image - how many pixels are there in width and height. While in Aperture a digital photo is in limbo, waiting to returned into a printed hard copy or viewed on a display. Only when we create a photo on paper or a display it will have physical dimensions in inches or cm, and it is up to the app that is creating the physical copy to ensure the dots per in that are needed for our purpose. When I export a photo from Aperture as a digital image file, I am only worrying about the pixel size, not about the dpi our ppi. I want to ensure that the exported files is saving all pixels. When dpi are added to the exported image file, they are a hint, how the photo should be displayed or printed. If the photo is to be shown on a display, 72dpi may suffice, if it is to be printed, I would use 250 dpi. But is up to the app importing the photo, if it will respect these hints or discard them. A digital image we export from Aperture may be used for many purposes - printing, displaying. Embedding dpi at export, makes only sense, if we are exporting for a specific web site that expects this specification or for printing right away.

BTW, when I export my Canon photos using JPEG original size (300dpi, Metadata included), the 300dpi are shown in Photoshop CS6 and preview.

I tested with

Thanks very much, Terence Devlin. I absolutely take your point about the physical variables, and I withdraw what I said about the visual sharpness of images, though I do take care that the same colour profile (Adobe RGB) is in use throughout. But I am concerned both with understanding the situation and with printing to a good standard. Please see my reply to léonie below.

Léonie, in my browser my reply appears further down in the string, I am afraid. But please let me know if you still can't see it and I will post it again.

It contains two questions — and, embarrassingly, as soon as I posted it, I realized what the answer to the first one was myself. So much for my past as a maths teacher! The answer, of course, is that I should have multiplied by 72 squared, not just by 72. But my second question, the practical one, remains, and I should be most grateful for an answer.

Now I am seeing your reply. 🙂

But if I multiply 42" x 56" x 72 ppi, which, as far as I can see, should yield the same answer, I obtain a mere 169,344 pixels.

You need to multiply (42" x 72 ppi) for the height by ( 56" x 72 ppi ) for the width to multiply the width in pixel by the height in pixel.

That will give you 42" x 72 ppi x 56" x 72 ppi = 12 192 768 pixels, equal to 12.2 Mp, the same size as the iPhone pictures.

And secondly, will I get sharper prints if I type 250 or 300 in place of 72 into the 'Resolution' box?

Glad you guys worked the math out 😉

As for this question the answer is... yes, in theory. But it's here that all the other issues - quality of printer, colour matching, paper quality and so on - come into play. Frankly, I've printed images at home on a good quality Canon inkjet that looked flat and lifeless, then brought the same images to a professional photo printer and the difference was immense. So much so that I no longer print photos at home.

So the only way to know for sure is... trial and error.

I have obtained the answer to my concerns about 72 ppi — from a kind, knowledgeable and clear respondent to my post, similar to my first one here, in the Adobe Photoshop forum. What started my concern was that if, in Photoshop, I reduced the image size to a more practical small size, the ppi figure remained at 72. And the answer is: to turn off 'Resample Image'. If that is done, the ppi figure shown goes up as one reduces the image size, showing what will be the true (dpi) value of the resolution on the printed paper.