DPI vs PPI

[Garnick]

This is not a question, it is in essence a statement.  A statement that may be judged as a rant and never see the light of day in this forum, but I sincerely hope that will not be the case.  However, I will now pose a question - DPI or PPI, what are you talking about?  Well, at the risk of offending someone I will attempt to explain the difference.  Yes, I do realize that those two acronyms are in many cases interchanged, but in a forum of this nature I think it becomes rather confusing for those who are trying to learn Affinity Photo as their first image manipulation app.  DPI of course stands for Dots Per Inch, as we aware.  If we are not aware, we should be!  PPI stands for Pixels Per Inch and bears no relationship to DPI, absolutely none.  In an image file you are dealing with PPI(pixels per inch), or, image resolution.  When printing that image you are dealing with DPI(dots per inch), or, printing resolution.  In essence, you could send a high resolution image file(ppi) to the printer, expecting to get a high quality print.  However, if you mistakenly set your printer at a low printing resolution(dpi) you would be very disappointed with the results.  There's an old saying, "garbage in, garbage out".  However, in the scenario I have just described, that saying would be something like this - "quality in, garbage out".  So to package all of this into a form that would hopefully have everyone speaking the same language, here's the simple breakdown - PPI/pixels per inch refer to an image file, whereas DPI/dots per inch refers to the number of dots that the printer lays down to build that image.  The only time you would actually see pixels in a print is in the case where an extremely low resolution file has been sent to the printer.  But keep in mind that those pixels you might see are made up of dots laid down by the printer.  To perhaps sum this up in a more succinct manner - PPI = Image file, DPI = Printer.  I realize that if anyone actually reads this it may appear to be simply a matter of semantics.  However, semantics are what language is based upon, and in this case misused semantics can be very disturbing to one trying to learn the difference between DPI and PPI, and most definitely there is a difference.

[anon1]

https://forum.affinity.serif.com/index.php?/topic/17803-resetting-the-dpi-of-export-images/?p=81800

"Well actually dpi and ppi is just the very same." - me

- actually I´d also agree on your explanation but in reality I´d argue that a printer should just read ppi input and use that for it´s dpi and I think that´s also how it works (but on the other hand the printer guys always seem a bit special to me  :blink:) 

 

R C-Rs final reference to the discussion linked above http://www.cambridgeincolour.com/tutorials/digital-camera-pixel.htm

 

Affinity - Understanding DPI Tutorial https://vimeo.com/152999247

 

IMO DPI PPI is not worth any rant so i appreciate your discretion.

[Garnick]

https://forum.affinity.serif.com/index.php?/topic/17803-resetting-the-dpi-of-export-images/?p=81800

"Well actually dpi and ppi is just the very same." - me

- actually I´d also agree on your explanation but in reality I´d argue that a printer should just read ppi input and use that for it´s dpi and I think that´s also how it works (but on the other hand the printer guys always seem a bit special to me  :blink:) 

 

R C-Rs final reference to the discussion linked above http://www.cambridgeincolour.com/tutorials/digital-camera-pixel.htm

 

Affinity - Understanding DPI Tutorial https://vimeo.com/152999247

 

IMO DPI PPI is not worth any rant so i appreciate your discretion.

 

Well actually you are wrong, dpi and ppi are not the same at all, and i find it rather disturbing that anyone still thinks they are.  I hope I don't come across as arrogant or insulting, I'm simply stating a fact.  And actually your opinion of what a printer "should" do is also wrong.  Well, I suppose I shouldn't refer to your opinion as being wrong, it's the conclusion that's wrong.  I generally print at 1440dpi and with some more demanding customers 2880dpi.  What that means is that the printer will lay down either 1440 or 2880 dots per inch depending on my setting.  It has absolutely nothing to do with the resolution of the image file.  Most, if not all Epson Pro Graphic printers/large format have a native file resolution of 360ppi that they prefer, but they will of course print whatever ppi is sent.  I believe Canon printers prefer 600ppi files and HP 300, but I may be mistaken on the Canon numbers.  However, the preferred file resolution has nothing to do with the printer resolution which is set by the operator.  And by the way, I do understand both ppi and dpi and their relation to each other, but thanks for the links regardless.  I shall check them out.  

[anon1]

I thought printers take your input size in cm calculated from the ppi and pixel count and then print with their max resolution, sampling the image at the necessary frequency... Well printers are strange.

[crabtrem]

I found this pretty interesting based upon the topic of this conversation.

http://www.fastcodesign.com/3039564/the-difference-between-ppi-vs-dpi-explained-by-a-google-designer

[R C-R]

 

... actually I´d also agree on your explanation but in reality I´d argue that a printer should just read ppi input and use that for it´s dpi and I think that´s also how it works...

Unfortunately, it isn't that simple, mostly because many printing methods don't actually print "dots." Consider for instance the common ink jet printer. It doesn't print discrete dots of colored inks, it prints a microscopically fine spray of up to 6 or more colors of ink droplets that mix & spread somewhat when they hit the page. The Cambridge in Colour article I linked to in the other topic refers to that when it says "multiple dots are often needed to create a single pixel" but it is a bit deceptive in that these "dots" are typically much, much smaller than an image pixel & are not laid out next to each other as would be the case with dithering on a monitor screen.

 

EDIT: The more I read about the different kinds of printing technologies in use, the more I realize that the only part of the above that is not a gross oversimplification is the first part of the first sentence -- there is nothing simple about printing, whatever the method. Even the basic idea of the printed "dot" is much more complicated than it at first seems, because (among other things) they can overlap, have different shapes & density variations within & around their circumference, or react with the substrate (which may or may not be paper) in different ways.

 

Not only are pixels & dots not the same thing, they aren't even the same kind of things. Image pixels are not physical objects -- they have no inherent size or dimensional properties of their own. They cannot be subdivided into smaller parts. Dots are physical objects that do have inherent size or dimensional properties, but they also have a fine structure that varies with the printing process used to create them.

Edited April 17, 2016 by R C-R

[Garnick]

Unfortunately, it isn't that simple, mostly because many printing methods don't actually print "dots." Consider for instance the common ink jet printer. It doesn't print discrete dots of colored inks, it prints a microscopically fine spray of up to 6 or more colors of ink droplets that mix & spread somewhat when they hit the page. The Cambridge in Colour article I linked to in the other topic refers to that when it says "multiple dots are often needed to create a single pixel" but it is a bit deceptive in that these "dots" are typically much, much smaller than an image pixel & are not laid out next to each other as would be the case with dithering on a monitor screen.

 

EDIT: The more I read about the different kinds of printing technologies in use, the more I realize that the only part of the above that is not a gross oversimplification is the first part of the first sentence -- there is nothing simple about printing, whatever the method. Even the basic idea of the printed "dot" is much more complicated than it at first seems, because (among other things) they can overlap, have different shapes & density variations within & around their circumference, or react with the substrate (which may or may not be paper) in different ways.

 

Not only are pixels & dots not the same thing, they aren't even the same kind of things. Image pixels are not physical objects -- they have no inherent size or dimensional properties of their own. They cannot be subdivided into smaller parts. Dots are physical objects that do have inherent size or dimensional properties, but they also have a fine structure that varies with the printing process used to create them.

 

Thank you for weighing in on this topic.  And yes, I sometimes describe the difference between pixels and dots in this manner - image forming pixels are related to and created by light, since without light there would be no image formation at all.  Dots however are related to and formed by physical pigments.  By "pigments" I am not referring strictly to "Pigment based inks", although they do indeed contain a much higher volume of pigments than do dye inks.  Another way of putting it would be the following - one can hold a pigment in one's hand, but not so for an image forming pixel.  The volume of pixels(picture elements) on the camera sensor are referred to numerically(Megapixels), meaning the total number of pixels that can be generated(recorded) on that size and density of sensor.  In that case the number of actual "photo sites" on the sensor will determine the maximum number of pixels recorded.  One can physically clean the camera sensor, but not so for an image file.  The only way of "cleaning" the pixels in an image file is in an app such as Photoshop or Affinity Photo, or other such programs. 

 

Indeed, image forming pixels are not at all the same as the "dots" that a printer uses to construct a physical print from that same computer based image file.  And yes, you are correct with this statement as well, "there is nothing simple about printing, whatever the method.  Even the basic idea of the printed "dot" is much more complicated than it at first seems, because (among other things) they can overlap, have different shapes & density variations within & around their circumference, or react with the substrate (which may or may not be paper) in different ways."  I have to plead ignorance in reference to both Canon and HP Printers, since all of my printers have been, and probably will continue to be Epson models/varieties.  I have owned and operated the Epson SP4000, SP7600(24")x2, SP9600(44") and now the SP9900(44") printers, and on all or most of those printers the "dots" are indeed somewhat elongated(eliptical) shaped, not perfectly round.  And yes they do often overlap to some extent as well.  

 

I imagine some readers of my original post would perhaps describe it as being nit-picky, or perhaps hair-splitting, or as I previously mentioned, a discussion based solely on semantics.  Well, I suppose it could fit quite nicely into all of those categories, for without picking nits, splitting hairs and paying attention to semantics, where would we be?  In my opinion we would be right where we are now, having a discussion about two totally different entities that have become housed under one common umbrella.  Again, the acronym "DPI" is still used as a catch phrase for both DPI and PPI, as if they are essentially the same thing.  Once I learned the difference between those two concepts many years ago, it always amazed me how many people used that same "umbrella" then, but I thought perhaps that had changed by now.  Unfortunately I was wrong.  To finalize my diatribe on "semantics" I will say that all of what I have written was to perhaps shed a bit of light on the incontrovertible fact that there is a very definite difference between "dots"(DPI) and "pixels(PPI).  I very much doubt this will have any effect on those who wish to follow the lazy path of grouping both concepts under that same old umbrella, but I have at least been able to offer my own 2¢ worth to the cause.

 

At this point I shall exit - stage left, and follow the discussion as/if it continues.

 

Thank you all for joining in, it's been a blast!¡!   :)                

[mshakeshaft]

I have to say that Affinity shoots itself in the foot as a serious editing tool by using DPI in the 'resize document' box rather than the correct PPI.

[NobleValerian]

This is not a question, it is in essence a statement.  A statement that may be judged as a rant and never see the light of day in this forum, but I sincerely hope that will not be the case.  However, I will now pose a question - DPI or PPI, what are you talking about?  Well, at the risk of offending someone I will attempt to explain the difference.  Yes, I do realize that those two acronyms are in many cases interchanged, but in a forum of this nature I think it becomes rather confusing for those who are trying to learn Affinity Photo as their first image manipulation app.  DPI of course stands for Dots Per Inch, as we aware.  If we are not aware, we should be!  PPI stands for Pixels Per Inch and bears no relationship to DPI, absolutely none.  In an image file you are dealing with PPI(pixels per inch), or, image resolution.  When printing that image you are dealing with DPI(dots per inch), or, printing resolution.  In essence, you could send a high resolution image file(ppi) to the printer, expecting to get a high quality print.  However, if you mistakenly set your printer at a low printing resolution(dpi) you would be very disappointed with the results.  There's an old saying, "garbage in, garbage out".  However, in the scenario I have just described, that saying would be something like this - "quality in, garbage out".  So to package all of this into a form that would hopefully have everyone speaking the same language, here's the simple breakdown - PPI/pixels per inch refer to an image file, whereas DPI/dots per inch refers to the number of dots that the printer lays down to build that image.  The only time you would actually see pixels in a print is in the case where an extremely low resolution file has been sent to the printer.  But keep in mind that those pixels you might see are made up of dots laid down by the printer.  To perhaps sum this up in a more succinct manner - PPI = Image file, DPI = Printer.  I realize that if anyone actually reads this it may appear to be simply a matter of semantics.  However, semantics are what language is based upon, and in this case misused semantics can be very disturbing to one trying to learn the difference between DPI and PPI, and most definitely there is a difference.

I don't believe it's simply a matter of semantics.  I'd like to see this issue corrected.

[NobleValerian]

Thank you for weighing in on this topic.  And yes, I sometimes describe the difference between pixels and dots in this manner - image forming pixels are related to and created by light, since without light there would be no image formation at all.  Dots however are related to and formed by physical pigments.  By "pigments" I am not referring strictly to "Pigment based inks", although they do indeed contain a much higher volume of pigments than do dye inks.  Another way of putting it would be the following - one can hold a pigment in one's hand, but not so for an image forming pixel.  The volume of pixels(picture elements) on the camera sensor are referred to numerically(Megapixels), meaning the total number of pixels that can be generated(recorded) on that size and density of sensor.  In that case the number of actual "photo sites" on the sensor will determine the maximum number of pixels recorded.  One can physically clean the camera sensor, but not so for an image file.  The only way of "cleaning" the pixels in an image file is in an app such as Photoshop or Affinity Photo, or other such programs. 

 

Indeed, image forming pixels are not at all the same as the "dots" that a printer uses to construct a physical print from that same computer based image file.  And yes, you are correct with this statement as well, "there is nothing simple about printing, whatever the method.  Even the basic idea of the printed "dot" is much more complicated than it at first seems, because (among other things) they can overlap, have different shapes & density variations within & around their circumference, or react with the substrate (which may or may not be paper) in different ways."  I have to plead ignorance in reference to both Canon and HP Printers, since all of my printers have been, and probably will continue to be Epson models/varieties.  I have owned and operated the Epson SP4000, SP7600(24")x2, SP9600(44") and now the SP9900(44") printers, and on all or most of those printers the "dots" are indeed somewhat elongated(eliptical) shaped, not perfectly round.  And yes they do often overlap to some extent as well.  

 

I imagine some readers of my original post would perhaps describe it as being nit-picky, or perhaps hair-splitting, or as I previously mentioned, a discussion based solely on semantics.  Well, I suppose it could fit quite nicely into all of those categories, for without picking nits, splitting hairs and paying attention to semantics, where would we be?  In my opinion we would be right where we are now, having a discussion about two totally different entities that have become housed under one common umbrella.  Again, the acronym "DPI" is still used as a catch phrase for both DPI and PPI, as if they are essentially the same thing.  Once I learned the difference between those two concepts many years ago, it always amazed me how many people used that same "umbrella" then, but I thought perhaps that had changed by now.  Unfortunately I was wrong.  To finalize my diatribe on "semantics" I will say that all of what I have written was to perhaps shed a bit of light on the incontrovertible fact that there is a very definite difference between "dots"(DPI) and "pixels(PPI).  I very much doubt this will have any effect on those who wish to follow the lazy path of grouping both concepts under that same old umbrella, but I have at least been able to offer my own 2¢ worth to the cause.

 

At this point I shall exit - stage left, and follow the discussion as/if it continues.

 

Thank you all for joining in, it's been a blast!¡!   :)                

Again, I think it's an important distinction.  And it's my only complaint with Affinity so far, so I'm going to whine loudly!