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Pixels per inch and not Dots per inch


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1 minute ago, MikeW said:

As regards an image, and only an image, if I were helping a user modify an image, what would I call these 4 things outlined in red?

Screen pixels? Image pixels? Artifacts created by lossy compression? Perhaps something created by a resampling algorithm? Without a clearly defined context, how would anybody know which of those things they are?

Saying something is "an image, and only an image" is not enough to do that. Image itself is a generic term that means different things in different contexts.

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21 minutes ago, R C-R said:

Screen pixels? Image pixels? Artifacts created by lossy compression? Perhaps something created by a resampling algorithm? Without a clearly defined context, how would anybody know which of those things they are?

Saying something is "an image, and only an image" is not enough to do that. Image itself is a generic term that means different things in different contexts.

No one here is talking about computer screens (except possibly only in your own mind).
No one is talking about artifacts, though that doesn't change the discussion (except possibly only in your own mind).
No one here is talking about compression, or resampling algorithms (except possibly only in your own mind).

What is being talked about (lately in the thread, anyway) are bitmap images. Which you certainly are smart enough to figure out in every context. That you conflate terms and the discussion itself with other issues is, well, dumb. You are certainly smart enough to follow the plot. You just prefer to conflate things for your own end.

So re-read my post and insert the term bitmap image.

But as I sincerely doubt you will stick to the plot, I'll answer for you.

A bitmap image is comprised of pixels, not dots. The 4 pixels I outlined in a screen shot are just that, pixels. No matter the shape of a pixel, there are X number of pixels per unit of measure (typically expressed as an inch). The proper term for that is pixels per inch (or abbreviated as PPI).

But hey, go ahead and conflate things so you can continue to be "smart."

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The "plot," if you want to call it that, is about how to specify image files sent to a printing service in "Pixels per inch and not in Dots per inch." That is literally the title of the topic.

The rest of it is about if or how it would make sense to do that. If you consider that conflating the plot, so be it.

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This conversation is going nowhere …

The explanation by >I< at the top of this thread more than adequately describes what is generally excepted as the correct use of the terms PPI and DPI. There are endless books, web tutorials etc which explain the terms in pretty much the same way. To argue any other way is wrong and misleading to those who perhaps do not have the benefit of prior knowledge of the subject.

We need to put an end to the current misuse of the terms and I really think the developers need to step in and address this issue.

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58 minutes ago, >|< said:

What is this thing that might require a dozen or more different terms to make "right"?

The "thing" is context. I have already mentioned some of them, but each of the various things that in one context or another is considered a picture element would need to have its own term that unambiguously makes that context clear; otherwise, those obsessed with accurate terminology will consider anything defined with generic terms like pixel or dot as "wrong."

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28 minutes ago, >|< said:

The context was unambiguous in the opening post.

It was originally, but that changed when @Ron Shutlar said this:

Quote

I my opinion the DPI reference needs to be removed and PPI inserted instead. I  agree with some of the users of Affinity Photo, it has no place within  the software package. The sooner it is removed the better. No other photo editing software that I have used contains DPI.

When people post opinions, is it really a surprise when that triggers a debate?

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4 minutes ago, >|< said:

PPI is pixels per inch and the word pixel has only one meaning in Affinity software; therefore, there is no ambiguity with PPI.

"Pixel" does not have only one meaning, in Affinity or anywhere else. See for example https://www.merriam-webster.com/dictionary/pixelhttps://whatis.techtarget.com/definition/pixel or https://www.techopedia.com/definition/24012/pixel.

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2 minutes ago, >|< said:

Lol, so tell us more than one meaning for the word pixel in Affinity software.

Are you suggesting that the difference between an image pixel & a screen pixel somehow does not apply to Affinity software?

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11 minutes ago, >|< said:

Pixel has the same meaning in both of these contexts!

Nope. The term "screen pixel" generally refers to the physical pixels of displays, like the fixed size pixels in the arrays of LCD, OLED, plasma, & similar display panels. They are what we mean when we talk about 'native' screen resolutions or the 1280x768 pixel minimum display size system requirement for Affinity products.

Image pixels are displayed using different numbers of screen pixels (like at 'actual size' or at various zoom levels) on display panels but screen pixels & image pixels are not the same thing.

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3 hours ago, >|< said:

Your word game is silly. The word pixel has the same meaning in your example of "screen pixel" versus "image pixel". The actual pixels are in different places, but the word pixel has a consistent meaning.

This is not a word game. These two types of pixels are not just in different places, nor does the word always refer to the same consistent & unchanging thing. For example, the display panel on my iMac actually has 3,686,400 usable screen pixels arranged in a 2560 x 1440 pixel array. Each of the pixels in this array is always & forever in exactly the same place on the panel. Neither their position nor their size can be changed by software or by any other means. They are invariant & immutable.

Clearly, this not true for image pixels. Their placement on the display can be changed using scroll bars, the View Tool, the Transform panel, etc. They can be displayed at different sizes using the Zoom Tool & their actual sizes can be changed using the Transform panel, the Photo Liquify Persona or the equivalent in other software apps, & so on. They are neither invariant nor immutable. If nothing else, that they can be manipulated using the Transform panel should make this totally obvious.

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On 1/3/2019 Guest said:

You can call them ‘sardines’ and ‘rainbows’, it doesn’t matter. It’s about communication and ensuring everyone understands the language. NASA’s Mars Climate Orbiter failed because the wrong units were used - give a printing lab the wrong info and they don’t pick up the error you’ll crash and burn-up.

PPI refers to the pixel resolution of a digital image, DPI refers to the density of ink dots on paper. The nuances of the terminology can be discussed ad infinitum but the bottom line is this is the industry standard. To suggest the terms are ‘interchangeable’ is incorrect and lazy.

The developers should set a good example and use the correct terminology.

But why is Pixels Per Inch the correct terminology ?

Most of the world uses millimetres, all of Europe, China, Japan etc. They don't use the out-of-date imperial inches. Why should they be forced to ?

I would say that far more people use digital images for display on a screen or some sort, rather than for printing and certainly not for for printing using inches. Inches are irrelevant for screens.

Lines Per Inch or Dots Per Inch were being used in printing for hundreds of years before pixels existed. So who decided Pixels Per Inch was the standard and should take over the "per-inch" bit, which is unsuitable for measuring pixels.

I'm betting it was a printer in America ;)

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On 1/4/2019 Guest said:

For those who haven’t come across this already here’s an article that maybe helpful

 https://photographylife.com/dpi-vs-ppi

If you are going to quote articles to try and prove your case, try and make sure they are technically correct, or at least explain things properly rather than glossing over them.

"Let’s start with some definitions. DPI stands for dots per inch and refers to the resolution of a printer. It describes the density of ink dots placed on a sheet of paper (or another photographic medium) by a printer to create a physical print."

That is a poor description. 

Dots Per Inch refers to the the number of dots the printer can apply (the resolution), but when it comes to halftone images (which we are talking about) , they are made by varying the quantity of 'printer' dots. A typical imagesetter has a resolution of 2540 DPI (mine did) so the dots in a typical 150 LPI are made up of many smaller dots.

 

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4 hours ago, toltec said:

But why is Pixels Per Inch the correct terminology ?

Most of the world uses millimetres, all of Europe, China, Japan etc. They don't use the out-of-date imperial inches. Why should they be forced to ?...

I'm betting it was a printer in America ;)

Because it is?

No. It was an ISO committee that decided it.

But if it makes you feel any better, when PING* (PNG) format came around to the ISO to standardize, they decided centimeters (well, expressed as meters) was to be the standard. And it is. It is impossible to actually record pixels per inch in a PNG file. The units will be converted from PPI. But good luck finding software that will present that information to you in a GUI application. So perhaps it is a conspiracy...

*PING stands for P(NG) Is Not Gif.

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3 minutes ago, MikeW said:

But if it makes you feel any better, when PING* (PNG) format came around to the ISO to standardize, they decided centimeters (well, expressed as meters) was to be the standard. And it is. It is impossible to actually record pixels per inch in a PNG file. The units will be converted from PPI. But good luck finding software that will present that information to you in a GUI application.

FWIW, the Inspector window in the Mac Preview app will do that in the 'More Info' > PNG section:

1190166459_moreinfo.jpg.62caffa8942b2269ed59734aac68a174.jpg

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41 minutes ago, MikeW said:

Because it is?

No. It was an ISO committee that decided it.

Where did they decided this to be so? - There is no ISO standard for that AFAIK (even if the usage of the term PPI in this raster image/screen context is the correct usage).

On the net there are historical references for the term pixel (picture element) and it's usage, but no ISO standardization informations AFAI can see.

  • Richard Lyon: A Brief History of ‘Pixel’. In Digital Photography II, S. 1–15. SPIE, Bellingham 2006, ISBN 0-8194-6109-1 (PDF, 1,4 MB)
  • Alvy Ray Smith: A Pixel Is Not A Little Square, A Pixel Is Not A Little Square, A Pixel Is Not A Little Square! (And a Voxel is Not a Little Cube). Microsoft Technical Memo 6, 1995 (PDF, 80 KB)

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1 hour ago, v_kyr said:

On the net there are historical references for the term pixel (picture element) and it's usage, but no ISO standardization informations AFAI can see.

It's complicated but basically, there are different standards for different file types. Making it even more complicated, there are different standards developed over the years by different standards organizations, which may differ in some (usually minor) ways. So for example, this page contains info about the PNG image format &  the "PNG specification, Joint ISO/IEC International Standard and W3C Recommendation." 

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