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 Author Topic: Need help with a statement in the Understanding Resolution tutorial  (Read 893 times)
geezer
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 « on: January 03, 2013, 07:12:28 PM » Reply

At the very beginning of the tutorial is a description of the properties of an image.

I understand how an image 2160 pixels wide would yield an image 9" wide at a resolution of 240 pixels/inch.

I understand how that same 2160 pixel wide image could yield an image 6" wide at a resolution of 360 ppi.

Now I fall off the path of understanding. The tutorial states:

"Now, let's say you want to make a larger print — say one that was 14 inches wide. You would then end up with an image that was about 9.3 inches wide but more importantly one that would only have a resolution of 155 pixels / inch. This is not enough output resolution for a high quality print, as we'll see below."

Ok, I understand how spreading that 2160 pixel-wide image over a width of 14" would mean the resolution would have to drop to about 155 ppi. (2160/14=154.2 ppi).

But what does "You would then end up with an image that was about 9.3 inches wide " mean? The image is 2160 pixels wide. At 155 ppi, the document's width is 14". What does "an image that was about 9.3 inches wide" have to do with anything?

Maybe I'm just incredibly thick (my wife sometimes thinks so), but I can't follow this.

Tom

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digitaldog
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Quote
This is not enough output resolution for a high quality print, as we'll see below."

Basically, the threshold of minimum resolution (and this depends on the printer) is somewhere between say 180ppi and 200ppi. Of course you can use less pixels per inch but quality suffers. In the very, very old days (1992 or so) the very first contone printer I used was a Kodak XL-7700 dye sub. It had an output rez of 203dpi (you sent it 203ppi). Back then, that was still a big file for a 10x10 print. Why 203? Well Kodak found that was close to the minimum data needed to make a good print. Today, with a decent ink jet like an Epson, you can get away with 180ppi and at viewing distance, it will look fine.

Quote
At 155 ppi, the document's width is 14".

I get 13.9 so our math is damn close. Typo?
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Andrew Rodney
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hugowolf
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Yes, Would presume it is a typo. I think it should read "and that was about 9.3 inches high". I think he/she is assuming a 3:2 aspect ratio with an image that is 2160 x 1440 pixels.

Brian A
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geezer
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Aha! 9.3 inches high! Yes, that's it.

Making a 2160 pixel image 14" wide would make the 1440 pixel image height 9.3" high.

Thanks a lot.

Tom
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PeterAit
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You're not thick - the statement is garbage, it makes no sense at all. Ignore it. Other aspect of the tutorial may be useful, but this part is not. It's a result of people who think they are smarter than they are publishing stuff without peer review or copy editing.
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Peter
"Photographic technique is a means to an end, never the end itself."
View my photos at http://www.peteraitken.com
michael
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You're not thick - the statement is garbage, it makes no sense at all. Ignore it. Other aspect of the tutorial may be useful, but this part is not. It's a result of people who think they are smarter than they are publishing stuff without peer review or copy editing.

Is there something in the water today that is making people bitchy, turning a typo into a rude attack?

This is the third posting today of this sort.

Is civility going to be dead in 2013? If so then I'll shut this whole fuck'n place down.

Michael
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Alan Goldhammer
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Is civility going to be dead in 2013? If so then I'll shut this whole fuck'n place down.

Michael

If they are US citizens they have been watching too much of our Federal legislators in action.  The Canadians are a much more civil lot!
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Johnny_Johnson
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If they are US citizens they have been watching too much of our Federal legislators in action.  The Canadians are a much more civil lot!

Not based on Michael's comment!

Later,
Johnny
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Johnny Johnson
Cleveland, GA
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