PPI is not DPI

[R C-R]

PPI relates to digital file size/quality/density.

If that is always true, then what is the PPI of a vector object file, & how does it relate to its size/quality/density? What about PPI as it relates to the physical pixel groups of a display?

 

DPI relates to the conversion of an image file into a print affected by an inkjet printer which produces hard copy images by squirting ink onto paper at so many Dots of Ink per Inch.

 

As Mike (among others) pointed out, that isn't actually true. It is just a convention used to describe a more complex process in a generic way.

 

So how "correct" do we really want to be about all this? If a digital image file consists only of vectors, should PPI or DPI never appear in any dialog? Should DPI never appear without an explanation or some other indication that these "dot" units are not actually directly related to the size, number, or shape of the minuscule drops of ink deposited on the substrate by an inkjet printer, or for that matter that this relationship varies depending on the type of printing process, the RIP, & any other software used to process the image data for printing or display?

[Stan Carmichael]

Keith,

 

I "Suggest" nothing at all, I explained how and why DPI has become a popular, if not always correctly used term.

 

It is an indication of language migrating to popular acceptance.

 

Remember:  "Energy Flows in the Path of Least Resistance". 

 

The next time someone asks you for a Kleenex, do they want a tissue or a certain brand of tissue?

 

You live in England so, you might 'Hoover' instead of vacuum. We all know Hoover is a proper-noun not a verb.

 

Both popular, both technically incorrect but now, accepted language.

 

The term DPI will flourish in our language, it rolls off the tongue well and sounds cooler than LPI or PPI. Not correct at all, but cool and commonly acceptable.

 

Stan

[NobleValerian]

Marj, you are right-on!

 

But don't hold your breath...

 

I have worked with electronic imaging solutions since 1981 and at the outset of "Desktop Publishing" in the late 80's the language migrated from 'technically correct' to 'marketing cool', it would be difficult to reverse the trend now. It was more important for copier companies to communicate with corporate types than to conform to technically correct terms. This pre-dates digital workflow in photography by over a decade.

 

Follow the money and you'll find the answer.

 

Selling laser and inkjet printers into the office market was, and still is, huge business. Additionally, most graphics software is also geared to a less sophisticated (non-professional) market. Thirty-years ago presentations were created by graphic artists not office-clerks and sales-people, and it shows...

 

So, as long as there is money to be made, we will favour 'cool' over 'correct' and 'common' over 'correct' because no-one chooses  'correct' over 'money and acceptance'.

 

For those who might be interested:

 

DPI = the pitch or frequency of a print head in a laser or inkjet printer. It is not a measurement of dimension. It tells us the number of laser beam exposures or inkjet droplets used to image per-inch of image.

 

PPI = the number of pixels-per-inch in a raster image (tiff, jpeg, png etc.). Metric uses the term 'res' for lines per mm. e.g. 'res12' which = 304ppi.

 

LPI = "Lines-per-Inch"  LPI referred to screen frequency for half tone images and graphics used to make printing plates and display resolution. For example, we print the photos in a magazine @ 175lpi which requires tiff files of 300ppi for ideal quality.

 

Enjoy, but don't waste time over this,

 

Stan

You're right about that.  The typical "4K" TV is a good example.  I'm glad people want to discuss it, but the only message that I want to send is straight to Affinity, and that's that I don't agree with using it, and I'd love to see it changed.  As I've mentioned before, they have great software, and thanks to them, I'll hopefully be dropping my Adobe subscription soon.

[NobleValerian]

If that is always true, then what is the PPI of a vector object file, & how does it relate to its size/quality/density? What about PPI as it relates to the physical pixel groups of a display?

 

As Mike (among others) pointed out, that isn't actually true. It is just a convention used to describe a more complex process in a generic way.

 

So how "correct" do we really want to be about all this? If a digital image file consists only of vectors, should PPI or DPI never appear in any dialog? Should DPI never appear without an explanation or some other indication that these "dot" units are not actually directly related to the size, number, or shape of the minuscule drops of ink deposited on the substrate by an inkjet printer, or for that matter that this relationship varies depending on the type of printing process, the RIP, & any other software used to process the image data for printing or display?

My understanding of how printers work is that vector and bitmap images are both processed as bitmap by the print software, so it's still just a question of resolution, which we all know vectors handle very efficiently.  And regardless, I don't create an infinite document in Designer, it still has pixel dimensions, and the pixel density of that document still has less of an impact on quality than the printer DPI, paper, and finish.

[NobleValerian]

None of that really answers the question I asked. What practical, real world benefit would there be to changing "DPI" to "PPI" in things like the new document or "Resize Document..." dialog boxes in the Affinity apps?

Yeah, it answers it very clearly.  And the main benefit is that it would be correct, instead of common.

[R C-R]

It is an indication of language migrating to popular acceptance.

It is also an indication of the practical, down to earth, real world need to refer to ever more complex technical processes in simple, concise terms.

 

It isn't just that PPI & DPI are not the same thing. It is also that neither "pixels" nor "dots" individually always refer to the same things, since each can refer to different kinds of things, depending on the context & how precisely that is defined or understood.

 

Just like if we always had to stop & explain exactly what we really meant by "Kleenex" or "Hoover," if we had to do the same thing for "pixel" or "dot" or any term involving either of those words, then what would we actually accomplish that made any difference to anyone?

[NobleValerian]

But even here there is confusion.

 

PPI is not a demarcation of quality. It is only dimensional.

 

Image PPI also does not directly relate to the physical dots per inch on a printed page, except when the image's physical dimensional PPI matches the physical capabilities of the output device. These days that is rare.

 

A physical printer, be it an inkjet or imagesetter, will generally have more printer dots per inch than the image being imaged has physically. That is, a typical inexpensive inkjet using extrapolated dpi may use 720 printer dots per inch to print say an image being sent to it having 300 ppi. And a typical output resolution is 2400 dots per inch regardless of the image being set to it.

 

While I would welcome Serif changing the label for DPI to PPI, it is after all, just a label and a mathematical unit for various operations and those operations are dimensionally agnostic. I still have found no "real life" person that is confused by which term is used.

 

But either way there requires a modicum of explanation as to the effect of PPI/DPI to someone that is new to image manipulation. But once one gets it, they easily interchange those two terms just like we all have done.

 

I have a feeling I should have stayed out of another near-pointless thread. Serif has made clear this is being reviewed. No amount of our banter will change that end decision.

 

Mike

Maybe some amount of banter.  Users have been asking for it to be changed for about 2 years.  It doesn't affect how I use the software, it's just irksome that it's wrong.

[Fixx]

I could say pixels that I have onscreen are kind of dots. Also, printer (or more often imagesetter) dots are frequently called device pixels.

Never mind, please continue the war  ^_^

[R C-R]

To settle this once & for all, I propose all Affinity apps should replace every occurrence of "DPI" with this: _•PI

(suitably sized & aligned, of course)  :D

[NobleValerian]

NobleValerian,

 

Stirring up this many old threads is not the right way to behave in a forum. I suggest that you link to these threads from one new post in one of the current threads. It's more work but means that the conversation is kept in one place. 

 

You are flooding, which is exactly what you said you didn't want to do.

And it's not.  You sent me to a locked topic linking these threads and told me this is where I should engage.  Which was great.  I had no idea users were asking for this to change for 2 years. 

[NobleValerian]

NobleValerian, on 23 Dec 2016 - 6:26 PM, said:

I feel this was a poor choice, and I'd very much like to see it changed.

I respect your thoughts, I hope you can respect ours too.

 

 

I respect that everyone has a perspective, but if Affinity is unwilling to change it, I think they should just state that, and state why.  "We believe DPI is less confusing to our users than PPI, even though it's not very accurate.  We understand many of our users would like it to be changed, but everyone who understands the difference is only affected by our lack of accuracy and professionalism, and it makes no difference to their workflow whatsoever, so it will never be a priority for us."  (Obviously you don't have to say you lack accuracy and professionalism, that's just the view some of your users have when they see DPI instead of PPI.)

I don't have to agree with that choice to respect it, but I can't tell from staff responses over the last 2 years whether this is truly the case, and I'm being patronized, or if there is a legitimate chance your company will consider correcting this in a future update.  I respect that your various staff have thoughts on this, but I have no idea where "Affinity" stands on this.  It's just not clear what the decision is.  One staff member says they agree that it should be changed, one says it's too much of a hassle to change because users are more likely to understand the wrong term, one says it's a perfectly acceptable term, and another says all suggestions are considered.

Which is why I reached out to Affinity, and not to the Affinity community.  Your users can't decide to change it, so I don't really have a case to make for them.  We can just "debate" among ourselves for 2 years without ever getting a real decision on it.

Edited December 25, 2016 by NobleValerian

[NobleValerian]

I could say pixels that I have onscreen are kind of dots. Also, printer (or more often imagesetter) dots are frequently called device pixels.

Never mind, please continue the war  ^_^

That's true, a loose definition of pixels could include the term dots, and a loose definition of dots could mean pixels.  However, the same way the pixels of an image file aren't related to printer DPI, they're also not closely related to physical screen pixels.

 

A physical pixel on your screen uses 3 components (RGB) to represent one piece of pixel information from your file, and depending on your monitor, those components could be all sorts of shapes (including circles and rectangles, whatever shape the diode is), but you could still use your entire monitor (millions of pixels) to display one pixel of file information on your screen.  And from my understanding, printers print bitmaps whether the source file is "vector" or "raster".  So, from my perspective, PPI is still the most appropriate/correct way to describe the pixel density of your digital file.  It's context based, and in the context of a digital file, I say pixel is correct, and dot is not.

[Alfred]

I respect that your various staff have thoughts on this, but I have no idea where "Affinity" stands on this.

 

"Affinity" isn't an entity that has a stance on anything: it's the name of a software suite (or a "brand", if you like). The name of the company producing the software is Serif (Europe) Ltd.

 

from my perspective, PPI is still the most appropriate/correct way to describe the pixel density of your digital file

 

A digital file doesn't have a pixel density, it only has pixel dimensions. Pixel density only comes into it when you're sending the contents of the file to an output device.

[NobleValerian]

"Affinity" isn't an entity that has a stance on anything: it's the name of a software suite (or a "brand", if you like). The name of the company producing the software is Serif (Europe) Ltd.

 

 

A digital file doesn't have a pixel density, it only has pixel dimensions. Pixel density only comes into it when you're sending the contents of the file to an output device.

Fine, then I have no idea where the Affinity team, or Serif stands on this.

 

A digital file *does* have a pixel density, and it *does* only come into it when you're sending the file for output, but the file still needs to tell the printer how many of it's pixels should fit into a set amount of space.  And that information is set and stored in the file.

[Alfred]

A digital file *does* have a pixel density

 

Here is a digital file which should be familiar to you. What is its pixel density? 

[NobleValerian]

Here is a digital file which should be familiar to you. What is its pixel density? 

96

[Alfred]

96

 

In that case, why does IrfanView report a print size of 1.39 inches square (based on an assumed value of 72, since the file apparently doesn't provide the information itself)? :huh:

[NobleValerian]

In that case, why does IrfanView report a print size of 1.39 inches square (based on an assumed value of 72, since the file apparently doesn't provide the information itself)? :huh:

I don't know much about obscure old image viewers, you can talk to IrfanView or Affinity about that.  I had little to do with the image you sent me, but it still has a pixel density, probably because my monitor has a pixel density.

 

http://orig14.deviantart.net/50fd/f/2016/360/d/1/untitled_by_noblevalerian-dasz1oq.png

 

The image *I* created and uploaded also has a pixel density (of 300), even though it's just a JPG, and that info is stored with the file.

 

http://orig04.deviantart.net/315f/f/2016/360/9/6/untitled_by_noblevalerian-dasz29t.png

 

And yes, it also annoys me that Windows is calling it DPI, especially since the program that created the file uses PPI.

 

Some file types don't store PPI or DPI, because it's just not relevant.  Even in the scenario where the PPI is not relevant to the typical display of the file type, you're still doing the same math if you want to print it.  It may not matter, or may not be prudent to specify PPI, because one monitor displays 72 pixels every inch, and one displays 96, and one 102, and one 288, or whatever.  The data is still measured in pixels.  If you want an image without pixel data to print well, and it doesn't have PPI (or DPI), then you still need to figure out how many pixels wide it should be to give enough information to print with good detail.  If the standard is 300, it doesn't matter that your document doesn't say 300 PPI (or DPI), because you still told it that you want to to be 1800 px by 1200px, so that it prints well at 6 in by 4 in.  If you don't understand that, and all you know is that you need it to be 6 in by 4 in, then you need to understand how much pixel data is suppose to fit into that space.  A 6in by 4in document at 1 DPI is not a lot of information.  And I feel that if you don't understand that your document is going out as pixels whether you set it in points, inches, feet, yards, mm, cm, or meters... you probably should.

 

I heard what Affinity is saying, so I've asked popular printers why they say DPI, and asked for them to correct it, too.  I'm guessing not much comes of that either.  If you're going through the trouble of telling me my print quality is a combination of my print DPI, and print LPI, then it's confusing to tell me that you need my document to be at a DPI that doesn't match your print DPI, because now we're talking about two different DPI numbers in the same context.

 

Which is why you have a help section explaining what DPI is, then a help section explaining what your document should include to print properly, then a help section describing the minimum document dimensions in multiple units, then a help section with templates to make sure customers don't screw it up, but then *STILL* getting print issues from improperly sized files from confused customers!

 

Why doesn't the whole world just work in pixels?  Keep it simple.  "If your document isn't exactly these pixel dimensions for this final print size, we're not going to print it.  Your PPI, or DPI, is totally irrelevant.  These exact pixel dimensions or you get nothing.  The end."

[Alfred]

Some file types don't store PPI or DPI, because it's just not relevant.

 

Exactly! I guess you've changed your mind in the three hours that have elapsed since you wrote this:

 

A digital file *does* have a pixel density, and it *does* only come into it when you're sending the file for output, but the file still needs to tell the printer how many of it's pixels should fit into a set amount of space.  And that information is set and stored in the file.

 

If and when a digital file includes pixel density information, it's only a recommendation which software (e.g. an image editor or a printer driver) can either respect or ignore. It isn't an inherent property of the image.

[NobleValerian]

Exactly! I guess you've changed your mind in the three hours that have elapsed since you wrote this:

 

 

If and when a digital file includes pixel density information, it's only a recommendation which software (e.g. an image editor or a printer driver) can either respect or ignore. It isn't an inherent property of the image.

Exactly what?  You said:

 

A digital file doesn't have a pixel density, it only has pixel dimensions.

That's wrong.  A digital file does have pixel density.  I just showed you an image of a JPG with pixel density as an inherent property of the image.  Not *every* digital file is an image file, and not *every* digital file has an inherent need for pixel density.  A JPG has inherent pixel density, TIFF has it, GIF doesn't seem to store/remember one that you assign (but will always have my display resolution assigned when I open it), and a PNG won't show it when I right click and look at properties - However, if I open a PNG I saved at 300 PPI, it will still be 300 PPI, and the exact same image saved at 72 PPI will still be 72 PPI.  That's even true if I export it from Photo and open it in Photoshop, so where does that info come from?  A PNG still seems to know if it should be 72 or 300 PPI, and I assume that's inherent to the file and not the software magically guessing which number I want to see.

 

Since Photo or Photoshop will always display a value in this field, and a printer would have no idea what to do if that information wasn't provided in some way (say for like a vector, which just says, "the highest possible bitmap resolution you can muster in this predefined amount of space" (and my knowledge on that process isn't exceptional), or a GIF which seems to be variable based on your display resolution), I think it's safe to consider pixel density an inherent property of a digital file.  And it's not a recommendation  >.>  The printer driver doesn't say, "Oh, I see here your Affinity Photo file is 150 DPI, but all machines know 350 DPI is better so I'm going to go ahead and use that instead.  You don't mind if I extrapolate from your file to create some data that doesn't exist there, do ya?  Greaaat."  -.-

[MikeW]

The field that holds the DPI information is not a representation of pixel density. It is only a two-byte informational field that as can be demonstrated may not even hold information. Where an image file has this DPI information, it is/can be used for initial sizing and if it is not present, both the OS and applications make an assumption based upon a default OS figure.

 

Images have no pixel density per se. They simply have pixels. All that really matters when it comes to print is what is called the effective resolution.

 

Mike

[NobleValerian]

The field that holds the DPI information is not a representation of pixel density. It is only a two-byte informational field that as can be demonstrated may not even hold information. Where an image file has this DPI information, it is/can be used for initial sizing and if it is not present, both the OS and applications make an assumption based upon a default OS figure.

 

Images have no pixel density per se. They simply have pixels. All that really matters when it comes to print is what is called the effective resolution.

 

Mike

The effective resolution is related to scale, dependent on the actual resolution, and it's far from the only thing that matters when it comes to print.  For those that don't know, effective resolution basically just means that printing a 300 PPI image at 200% would give it an effective resolution of 150 PPI, and it wouldn't look great, but printing a 600 PPI image at 200% would give it an effective resolution of 300 PPI, so it would still look pretty good.  Important to consider, but based on a default, inherent value.  It just means you need to think about scaling when printing because you CAN print a great quality image larger and get good results, but you need to print a low resolution image smaller to change it's effective resolution, and get good results.

 

If it's just a two-byte field that doesn't mean anything, why include it?

[NobleValerian]

I'm not feeling like this has been super productive.  I never wanted a debate about the merits of using PPI.  I doubt I come off very friendly in my posts, anyway.  I know where I stand, where some of the staff stand, and I would just like it to say PPI.  Users for two years have discussed this.  I've considered all the ways this could play out, and I've decided to make an official feature request and be done with it.  Hopefully this, and previous, discussions have a positive impact on that request, but I don't think I have much more to say about the topic.  It's *AWESOME* software, and feeling like DPI isn't the most appropriate term, for the tiny annoying amount of time I have to look at it every day, doesn't change that for me.

https://forum.affinity.serif.com/index.php?/topic/32620-a-checkbox-in-interface-preferences-to-show-ppi-instead-of-dpi/?p=158710

[GDPR-365024]

I was curious when I read the term 'pixel density' as I've not heard/read that before.

 

Here's Wikipedia's take   https://en.wikipedia.org/wiki/Pixel_density

[MikeW]

One cannot have an image in an application without effective resolution. It is impossible.

 

And one can have an image with a high effective resolution and have a poor print if the effective resolution exceeds the ability of the output device. Pixels will be tossed out in that case.