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export files DPI means nothing

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president of the Pendants Club

 

In which role you would presumably expect us to be hanging on your every word! :P


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Well, R, a pixel has an exact meaning.

Then what is it? Try doing a web search on "definition of pixel." What you will get (among many others) are things like this from Merriam-Webster, this from The Free Dictionary, or this from Webopedia, & more extensive ones like the Wikipedia entry.

 

Basically, it isn't that pixel has any one exact meaning; it is that it has several different ones, depending on the context.


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In which role you would presumably expect us to be hanging on your every word! :P

More likely, you would be busy organizing a mob to hang me shortly after my acceptance speech.  :o

 

We pendants are a vindictive lot.


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@R,

 

I'll leave you to the fruitless Internet search. 

 

This thread was/is about the pixel and how it relates to resolution and DPI as regards a bitmap image. In that regard, there is only one meaning. If you wish to conflate all the possible meanings into that/this discussion, so be it.

 

Good luck.

 

Mike

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I hesitated before joining this discussion as it seems to be getting a little heated which is not helpful to anyone. 

 

What the majority of people wish to know, in simple terms, is whether there is a difference between PPI and DPI.

 

I'm not a pendant, nor brilliant at maths, but I have been involved in digital photography for over thirty years and taught by some expert digital photographers. Yes, there is a practical difference although I agree that unfortunately the terms seem to be used indiscriminately in daily use. As another contributor wrote above you need to consider the context they are used in. 

 

The best way I can explain it is that PPI relates to the file size. If you have a file 6 inches by 4inches at 300 PPI and then change it to 6 inches by 4 inches at 100 PPI, then that file size is considerably smaller that the original file. The follow on from that is each of the pixels in the smaller file covers a greater area so you will lose detail [sharpness] more quickly if you zoom in on an area than you would in the larger file. This applies also to when you come to print the file. The larger file with more PPI will print show more detail [be sharper] than the smaller file.

 

DPI really should inly be used when discussing printing and refers to the number of drops per inch the ink is applied at. Print the same  file at a lower number of DPI and then print it again at a higher number and compare the two. The greater number of DPI the more detail [sharper] the print will be. 

 

At the risk of confusing readers the type of paper you print on can also affect the apparent sharpness of the print. The same file printed on a glossy type surface can appear sharper than when printed on a 'art type matt' paper.

 

I may not have explained the above as precisely as I would wish but before any come back at me please read the book Adobe Photoshop for Photographers version CS5 by Martin Evening [Focal Press ISBN 978-0-240-52200-5]. Read Chapter 5 "Image Editing Essentials"  pages 289 to which covers this debate comprehensively and clearly. Martin Evening has been an acknowledged Photoshop guru for many years.

 

I cannot recommend it strongly enough, not only for this subject but anything to do with digital photography.

 

Hope this helps.

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MikeW's posts are facts. Period!

 

I entered pro photography and pro photographic printing in the late 70's. In the mid(ish) 80's I took time out for a couple of years and worked in prepress to um, figure out why my images that took me many hours to create were 'smashed' by the offset printing process (part of my work at that time was technical / medical therefore calling for precise reproductions).

 

So, I started looking at the world in terms of dots! (so to speak) ...and learned a truck load - all the way to our current digital stuff... 

 

The YouTube link I posted above nails it. Please take the time to look, listen and understand it.

 

Oh: A really good book (although maybe only in libraries now) is 'Real World Scanning And Halftones'  2nd Ed  ISBN 9780201696837  (1999)

 

 

 

Edit: There is a 3rd version of Real World... 


https://www.peterdinnan.com/     photography with elements of mood, abstraction, pareidolia, gestalt and the morphics

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The YouTube link I posted above nails it. Please take the time to look, listen and understand it.

The YouTube video is long (almost ½ hour) but in my opinion definitely worth watching from beginning to end. At about the 8 minute mark it makes an important distinction between halftone dots & what he calls halftone "spots." This makes it very obvious why DPI is meaningless other than for printed output -- a dot is just an abstraction that the printing process converts into spots we can see.

 

At the risk of further annoying the non-pendants, a similar distinction exists between image pixels & display pixels: image pixels are just abstract picture elements that the digital display process converts into display pixels we can see. This distinction is important because of its relevance to "actual size," "pixel size," "zoom to fit" & all the other view options that Affinity offers, & how that relates to dots, spots, & DPI.


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Wouldn't it be better if it said PPI then?

 

Yes.  Every time.  I don't know why they're fighting it so hard if they're "basically interchangeable".  Just use the correct term then!

 

I hesitated before joining this discussion as it seems to be getting a little heated which is not helpful to anyone. 

 

What the majority of people wish to know, in simple terms, is whether there is a difference between PPI and DPI.

 

I'm not .........

 

........I cannot recommend it strongly enough, not only for this subject but anything to do with digital photography.

 

Hope this helps.

 

Yes.  In summary, for all practical purposes, the program should be describing resolution in PPI.

 

Then what is it? Try doing a web search on "definition of pixel." What you will get (among many others) are things like this from Merriam-Webster, this from The Free Dictionary, or this from Webopedia, & more extensive ones like the Wikipedia entry.

 

Basically, it isn't that pixel has any one exact meaning; it is that it has several different ones, depending on the context.

 

Those loose definitions of pixel also depend on a loose definition of "dot", making them far less than ideal, while not directly related to the intent and purpose commonly associated with them in digital art and printing.

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Yes.  In summary, for all practical purposes, the program should be describing resolution in PPI.

 

Resolution means nothing except as an output term. PPI is dimensional.

 

Aside from the fact that I think PPI is more accurate as regards the dimensional properties of an image--whether that image is destined for screen or print--I don't believe there are many people that do not understand the usage as found in whatever application, or at least cannot come to understanding its usage.

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We use DPI because we don't know if you're going to print the document or export it as an image. If you print, then DPI = DPI, if you export, then DPI = PPI. Hence why we said the terms are used interchangeably across most software packages.

 

But this is not correct.  It doesn't matter whether you print or not.  Your exported PNG will have pixel dimensions and the PPI won't be relevant at all, so it's not correct to say it would be equal to PPI.  Furthermore, a 300 PPI image could be printed at 300 DPI, 600 DPI, 1200 DPI, or maybe 2400 DPI, so again, PPI is not relevant or appropriate to use in place of DPI.

 

It's one thing to say that so many people don't understand the difference, or that printers foolishly ask for DPI when they mean PPI, that you believe it would create a lot of confusion to change it.  I don't agree with that stance, but I understand it.  It's not understandable to say that they are interchangeable, or that DPI is ever equal to PPI.

 

While technically correct, this strict definition of DPI is only relevant to the internal mechanics of the printer; it's not a term you'd generally find in software.

I think it's safe to assume that whenever software does mention DPI, it means PPI.

So, DPI is *not* a term you'd generally find in software, but you guys decided to use it anyway?  And whenever someone mistakenly uses DPI it's safe to assume they mean PPI, but you still chose to use DPI?

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