Exported JPG resizing artefacts when set to 300dpi but not 72dpi

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Level 2

150 points

Exported JPG resizing artefacts when set to 300dpi but not 72dpi

When I create a JPG Export Preset that Sizes to Fit within for example 1200 x 1200 pixels, I have found that the resulting file has square artefacts if I set the preset to 300dpi rather than 72dpi.

I have 2 otherwise identical Export Presets (one 72 and other 300 dpi) and they give different results. At first I thought it was JPG artefacts, but the same thing happens with PNG exports if I change the dpi setting. I am starting with an original RAW file that is 6048 x 4032 pixels.

I checked the exported file in Safari, Preview and GraphicConverter and the same artefacts are there at 100% view.

I always thought that dpi was only a label and didn't affect the file, but clearly somehow it does.

Has anyone else noticed this odd effect?

24" iMac 3.06GHz 4GB RAM, Mac OS X (10.5.7)

Posted on May 19, 2009 11:31 AM

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Answer 1

D Anderson Author

Level 2

150 points

May 20, 2009 1:46 AM in response to D Anderson

Example of PNG at 300dpi showing square patterns in the detail
image: !http://homepage.mac.com/braeside/stuff/300.png!

Same file but at 72dpi is OK
image: !http://homepage.mac.com/braeside/stuff/72.png!

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Answer 2

markhead

Level 1

5 points

Jun 14, 2009 11:45 AM in response to D Anderson

the images appear the same on screen to me, i suspect that you are exporting the 300dpi pic with the same physical dimensions as the 72dpi and so aperture is uprezing to 300dpi and so creating pixelation in the process.

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Answer 3

Anatoli

Level 1

9 points

Jun 27, 2009 12:14 PM in response to D Anderson

Hello!

I have the same problem regarding these square artifacts, which are clearly visible on your demo-pics. Especially when I publish the photos from Aperture to mobileme. The quality is VERY bad and worse than when I'm uploading exported JPEGs from iPhoto.

JPEG exported from Aperture and published through iPhoto:
!http://gallery.me.com/afedynitch/100288/Berg-Land-207/web.jpg?ver=1246114068000 1!

And here is the same image published directly from Aperture, clearly showing these square artifacts:
!http://gallery.me.com/afedynitch/100280/_STA4314/web.jpg?ver=12461110810002!

I saw also some threads trying to solve this issue, but all of them suddenly stop or are referencing to other publishing sites. This seems to be the point when the fooled mobileme customers simply give up. And btw. the quality of both published images is absolutely poor, even on iPhone 🙂 ... anything else than PRO...

Cheers,
Anatoli

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Answer 4

D Anderson Author

Level 2

150 points

Jun 28, 2009 6:04 AM in response to Anatoli

Yes, I can see the same effect on your photo. Especially evident in the area of the tree.

I agree the quality is far from what we should expect from a Pro Photo product.

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Answer 5

Jun 28, 2009 9:50 AM in response to D Anderson

Could either of you highlight or mark-up the "bad image" to point to the artifacts? Nothing is apparent on my screen.

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Answer 6

D Anderson Author

Level 2

150 points

Jun 28, 2009 9:56 AM in response to D Anderson

I don't know how you cannot see the effect? - look at the tree in the foreground above. There are "squares" all over it. Maybe this is some artefact with my display? But odd it only affects one of the two photos. On my monitor the squares are about 6mm wide if that helps you spot them.

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Answer 7

Jun 28, 2009 10:03 AM in response to D Anderson

AH... yes. Now I see what you mean. There is like a barbwire grid overlay.... hmmm very strange.

I considered this export after I logged off. WHY would you do that anyway?

Your camera shoots at 72dpi. Why not just figure the size you REALLY need and do the export accordingly? 5000x5000.

JT

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Answer 8

D Anderson Author

Level 2

150 points

Jun 28, 2009 10:31 AM in response to D Anderson

Glad you can see it - I was about to do a subtraction between the images in PhotoShop to show the pattern.

The reason I was exporting at that size was for the web, I just wanted a 1200 pixel wide image for the web and was surprised at the poor result. Changing the dpi figure in the export preset, which shouldn't change anything to do with screen display of the image, (1200 wide in both cases) , radically altered the image's quality. In one case I got the pattern in the other I didn't.

I know how to get around this now (by using 72dpi) but I do not understand why it has to be so.

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Answer 9

D Anderson Author

Level 2

150 points

Jun 28, 2009 10:40 AM in response to John Thawley

The myth of DPI http://www.rideau-info.com/genealogy/digital/dpi.html

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Answer 10

Jun 28, 2009 10:41 AM in response to D Anderson

You're not getting "around" anything.

EVERYTHING is 72dpi unless you're outputting for print (offset or lab photo).

There is absolutely no reason to change the PPI setting. It's all the same. You are merely putting the program through a step it doesn't understand. The result is an anomaly.

The file is 72ppi right from the camera. You are NOT gaining any quality for the web or a monitor by changing the res to 300ppi. The web can't display it, your screen can't display it either. It should remain 72ppi.

Offset presses use 244ppi to 300ppi. Photo labs can use as low as 144ppi.

Again, raising the res to 300ppi is pretzel logic. It doesn't exist on the web or on your monitor.

JT

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Answer 11

Jun 28, 2009 10:42 AM in response to D Anderson

This supports my explanation.

JT

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Answer 12

D Anderson Author

Level 2

150 points

Jun 28, 2009 10:45 AM in response to D Anderson

I understand precisely what you are saying and I was not trying to use the DPI figure to do anything. It was just that for some reason an export preset I had was at 300dpi and I got this effect. Plainly changing the dpi figure should have no effect at all on the output file, but it has.

You also see that the other guy who was using Apple's mobileme export is having the same problem, they must be related problems as the effect is the same.

In the MobileMe case i don't think the user can change anything within Aperture to work around this.

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Answer 13

D Anderson Author

Level 2

150 points

Jun 28, 2009 10:51 AM in response to John Thawley

We are on the same wavelength John, I think . Just possibly slightly at cross purposes. 🙂

We both know that dpi means nothing for the screen, but Apple put a dpi box in there and you can change it, it does affect the output and shouldn't. I discovered this by chance, I wasn't trying to achieve some special end and know how to workaround it, but I still feel it is a bug in Aperture and reported it to Apple when I started this thread.

Hopefully this may alert others to check their settings in their export presets.

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Answer 14

Jun 28, 2009 10:51 AM in response to D Anderson

True... but there can be mathematical quirks. Notice how an image in Photoshop displays on your screen... if you're at 37% or something random, the image looks like crap. Magnify to increments like 25% or 50% and it'll smooth right out.

Aperture doesn't ship with any 300ppi presets, though.

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Answer 15

D Anderson Author

Level 2

150 points

Jun 28, 2009 10:54 AM in response to John Thawley

John, I'm not sure how I ended up with a 300 dpi export preset either, maybe I edited some preset that had been intended for print, I really don't know. But you can be sure if I can do it, so can some other fool 😉

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