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Pixels per inch and not Dots per inch


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5 hours ago, v_kyr said:

I don't meant the PNG file format, file format standardizations are nothing new to me. - I meant the terminology for Pixels Per Inch (PPI) here, where ISO has decided this at all.

To the extent it is defined at all, it is defined in the file format specifications. For example, in the previously mentioned joint PNG specification refer to the Physical pixel dimensions section, & to clause 3.1.33, where a pixel is defined in much the same way as in the 1995 Alvy Ray Smith article, as:

Quote

information stored for a single grid point in an image. A pixel consists of (or points to) a sequence of samples from all channels. The complete image is a rectangular array of pixels.

So for instance, in a PNG file if the Unit specifier has a value of 1, the two 'pixels per unit' values represent pixels per meter; otherwise they represent the dimensionless aspect ratio of the rectangular pixel array.

Standards like the joint PNG specification typically include both requirements & recommendations for encoders & for decoders & readers (thus the "Recommendation" in the title). As long as the requirements are met, the 'reader' software can display these values however it sees fit, including not at all.

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8 hours ago, v_kyr said:

I don't meant the PNG file format, file format standardizations are nothing new to me. - I meant the terminology for Pixels Per Inch (PPI) here, where ISO has decided this at all.

Exactly ! And why would an International Standards Organisation choose a standard that only applies to 10% of the international community who will need to use it?

 

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38 minutes ago, toltec said:

And why would an International Standards Organisation choose a standard that only applies to 10% of the international community who will need to use it?

They did not do that. As with the joint PNG spec I discussed in the post just before yours, the 'internal' dimensional unit (if specified) is metric, but the decoding, viewing, or editing software can display it in other units & still meet the requirements of the specification.

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2 hours ago, toltec said:

Exactly ! And why would an International Standards Organisation choose a standard that only applies to 10% of the international community who will need to use it?

 

I've looked and scanned over their documents, there isn't nothing like that. ISO hasn't defined something like that, they just use the term the same mixed up way as the rest of the world ...

iso_blabla.jpg.fa26c8d962a6fec18a0f7abea6d2827b.jpg

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1 minute ago, v_kyr said:

... they just use the term the same mixed up way as the rest of the world ...

Not exactly. That reference just says ppi is analogous to dpi. The usual definition of "analogous" is "Comparable in certain respects, typically in a way which makes clearer the nature of the things compared." 

It is certainly true that ppi & dpi are comparable in some respects, but of course whether that makes anything clearer about their nature to most people is open to debate ... & there certainly is no shortage of that all over the web, not just in these forums. xD

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Well it depends if it is used in the right context (which is mainly device dependent here) and if that is somewhere clearly (unequivocally) defined. - The prepress, printing and media sector usually has the right explanations for these terms (PPI vs DPI) and their usage.

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18 minutes ago, v_kyr said:

Well it depends if it is used in the right context (which is mainly device dependent here) and if that is somewhere clearly (unequivocally) defined.

True, but the context is not always (or even usually) unambiguously defined, nor does it always have to be. Other than to fuel debates like this one, all end users really need is enough clarity to use the software to get the results they want. That is why the terminology is so often "wrong" -- most of it is just what people have used for decades, even when they know it is not as well defined as it could be.

After all, do you really need to know that in the context of an image file, a pixel is really just a point sample (or a pointer to one), or that dpi & ppi are just different ways of specifying sample density, to know how to use the software?

BTW, those references you mentioned, or at least the English translations, don't get everything right either. No surprise there -- there is no way to distill everything relevant to the topic into a single short article or two.

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  • 10 months later...

I've gotta rant:

I am REALLY hoping that Serif makes it possible to SAVE one's choice of measurement units with the Publisher document, and that it will NOT be overridden by points EVERY time I save and reopen the document, or export to PDF and open that! This is happening in Publisher 1.7.3.481 (Sorry, I'm an American, and I've grown up thinking in inches. I understand DPI, or PPI, but not points or picas. I often produce PDF files, and those measurement units aren't what I need.

Please.

​Sharon

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I set the Document Units in a New Document and it sticks for all subsequent New Documents I make. I am using Mac OS 10.14.6 (Mojave). If you have a document which is set to points go to the Document Setup from the File > Document Setup... and set it there then save the file and it will open in inches. Now I have to go back and reset mine to picas.

829817292_ScreenShot2019-11-09at3_46_27PM.png.ed8f4589f6cad8665a52722ad21dd22d.png

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2 hours ago, Old Bruce said:

I set the Document Units in a New Document and it sticks for all subsequent New Documents I make. I am using Mac OS 10.14.6 (Mojave). If you have a document which is set to points go to the Document Setup from the File > Document Setup... and set it there then save the file and it will open in inches. Now I have to go back and reset mine to picas.

829817292_ScreenShot2019-11-09at3_46_27PM.png.ed8f4589f6cad8665a52722ad21dd22d.png

Thanks much, Bruce, but I'm in Windows 10 x64, and that doesn't seem to work for me. I've had to re-configure it as "inches" SO many times tonight, when it's the same document I already saved with "inches"!

​Sharon

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  • 1 year later...
On 1/2/2019 at 5:22 PM, Ron Shutlar said:

Hello Affinity Photo

Would you please inform me how I can change the document size from Dots per inch to Pixels per inch, as there does not appear to be a drop down box to change this setting. I do not print from my own printer, but send my photographs to a professional printing company, so it is imperative that I change this setting to PPI.

Thank you in anticipation

 

Happy New Year 

 

Ron

Hi, Scaling a picture down is usually not an issue, however growing its dimensions utilizing software program reminiscent of Photoshop will possible produce poor outcomes, it is very easy to convert dots per inch to pixels per inch by click here

Regards,

Daniel Smith

 

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