22 Replies Latest reply: Jul 14, 2014 11:08 AM by Doug.S RSS

    How can I set DPI for a document in illustrator?

    alexstk Community Member

      I'm designing a user interface for iPad (Resolution: 1024x768, DPI:132). Setting the resolution is a piece of cake but when I change the ruler unit to Centimeters, it shows the screen about 36x27cm which is not right (iPad screen is 24.3x19cm).

       

      Illustrator calculates these lengths based on the DPI. But when creating a new document the only available DPI's are: 72, 150, 300 (File > New > Raster Effect). I searched for the answer on this forum and googled it and looked into the help but couldn't find a satisfying answer. I know that Illustrator is a vector design program but there must be a way to set the DPI to an arbitrary value.

       

      How can I have a 1024x768px artboard in Illustrator that is 24.3x19cm? (DPI=132)

        • 1. Re: How can I set DPI for a document in illustrator?
          Wade_Zimmerman Community Member

          Illuststrator displays at 72ppi and  and the measurements are actually based on points. The raster effects settingoly affects the translation of the effect not the documennt.

           

          You ahould simply work in pixels and not concern yourself with cm.

           

          Then save for web and device were you can set the image size.

          • 2. Re: How can I set DPI for a document in illustrator?
            JETalmage Community Member

            Drawing programs like Illusrator are object based. An Illustrator file can contain any combination of scaleable vector paths (its main reason for existence), text objects, and raster images.

             

            Because those elements are each separate objects, there is no "pixel" count that actually means anything at the whole document or whole Artboard level. Illustrator's rulers are for actual measures, and a pixel is not a unit of actual measure. A pixel can be any measure.

             

            You can set an Illustrator Artboard to 1024x768 "pixels" according to its misleading rulers all day long, but that really means nothing other than that the Artboard size measures 1024 x 768 points (which is an actual unit of linear measure).

             

            If you then draw a vector path on that Artboard, the rulers may tell you it's "size" is 50 x 100 "pixels." But that is nonsense, since by definition there are no pixels in that vector object. The object is merely scaled to measure 50 x 100 points.

             

            You can then set some text on that same Artboard. the rulers may tell you the text height is 24 "pixels." Again that is nonsense, since there are no pixels in that text. Text glyphs are vector paths. The vector paths are merely scaled to measure 24 points.

             

            You can then import a raster image onto that same Artboard. The rulers may tell you the "size" of that raster image is 50 x 100 "pixels." Even now, that means nothing more than that the raster image is scaled on the page to the size of 50 x 100 points. That image could contain any number of pixels. For example, it may contain 500 x 1000 pixels in which case its PPI would be a ridiculous 720.  They'd all just be scaled down to a much higher per-inch count than the 72 PPI which Illustrator arbitrarily considers "100%."

             

            Or, that image may contain only 25 x 50 pixels, in which case its PPI would be 36.

             

            Moreover, there's nothing preventing your having both of those images onto the same Artboard at the same time. The rulers would tell you they both measure 50 x 100 "pixels". You can see that is nonsense. They each are merely scaled to measure 50 x 100 points, and that has nothing whatsoever to do with how many pixels they contain.

             

            But now suppose you export that file to a raster format. When you do that, everything on the Artboard—vector paths, text objects, and raster images—gets rasterized (or re-rasterized, i.e.; resampled in the case of raster images) to whatever number of pixels you specify in the export dialog, regardless of whether that's the so-called "Save For Web" dialog, or the more straightforward Export dialog. That's the only place that a document-wide "PPI" or number of pixels means anything, because you are now rasterizing the entire stack of individual objects to a single raster image.

             

            So don't even look for a "document PPI" or an "artboard PPI" or a document "V-pixels-by-H-pixels" count. There is none. This is an object-based vector (scaleable) program. The "Pixels" unit-of-non-measure is bogus. It's merely an interface "convenience" for those who want to think in terms of pixels, even when it's inappropriate to do so.

             

            As is made so obvious by the frequency of repetition of this very question in this fourm, that silly interface creates more confusion than convenience.

             

            JET

            • 3. Re: How can I set DPI for a document in illustrator?
              alexstk Community Member

              Thanks for the long reply but my question still remains unanswered. I undersdtand that everything is vector and pixel or inch are just a metaphore of how the image can be rasterized.

              But consider this problem: when designing user interfaces in Illustrator, the output usually is going to be a raster screen for example web page, or mobile application. What I want is simple: I want the ruler to show the measures correctly. If pixels and centimeters are inaccurate, they shouldn't be shown at all. The problem is that [apparently] illustrator only allows a predefined set of DPI (or PPI) when creating the document. I want to create a document with the DPI of 132 and I want my artboard and rulers to work correctly. Now "correctly" here refers to what is expected. If the artboar's width is 1024px and my DPI is 132, it should be 24.3cm. Now I don't care what calculations are being done behind the scene, but Adobe Illustrator doesn't show the correct "cm". So either it shouldn't show anything or it should allow me to set the DPI and show it correctly.

              • 4. Re: How can I set DPI for a document in illustrator?
                Wade_Zimmerman Community Member

                Like I wrote before your perception is at fault just work in pixels as there ia no such reference gi any other form of measurement for screen desig n or implementation.

                • 5. Re: How can I set DPI for a document in illustrator?
                  JETalmage Community Member
                  I undersdtand that everything is vector and pixel or inch are just a metaphore of how the image can be rasterized.

                   

                  I don't think you do.

                   

                  If pixels and centimeters are inaccurate, they shouldn't be shown at all.

                   

                  I didn't say the measures of Illustrator's rulers are inaccurate. I said that Illustrator's rulers are designed to indicate linear measure, not counts of pixels.

                   

                  What is the width, in inches, of a pixel? That's like asking "how high is up?"

                   

                  Because Illustrator's rulers indicate linear measure (as will be communicated to a printer) the only way "Pixels" can be used as a ruler unit is for Illustrator to arbitrarily assign a real measure to a "pixel". The measure it assigns is 1 point (1/72 inch). This is a throwback to Illustrator's print heritage (and what is still its primary designed purpose, despite pretenses to the contrary).

                   

                  It doesn't matter what size your Artboard is, if your output is going to be a raster image. Suppose you need a 1024 x 768 raster image. So long as you make your Artboard proportional to (the same aspect-ratio as) 1024 x 768 anything, you can export it to 1024 x 768 pixels when you export it.

                   

                  I could set up that Artboard as 1024 x 768 milimeters, while you set yours up as 1024 x 768 "Pixels" (which is really 1024 x 768 points). Either of us can export our Artboard to 1024 x 768 actual pixels.

                   

                  There is no PPI to worry about. PPI only applies to print. A web page doesn't pay any attention to PPI information; it just cares about pixel count.

                   

                  JET

                  • 6. Re: How can I set DPI for a document in illustrator?
                    alexstk Community Member

                    @JET

                     

                    OK, from what you say I understand that the solution to my problem is if I want an artboard to be 3x3cm, I can choose whatever square artboard (for example 30x30 pixels or 30x30 inches or even 90x90 "centimeters") because only when I'm printing or saving the image for the web, Illustrator will ask me the actual width.

                     

                    Now my problem has two sides:

                    1. I want to be able to set the lines and curves in terms of pixels.

                    2. I want to know how big a button is to check the usability if the finger can click on it. For example I want to know how big my 20x50 button will be when I print it.

                     

                    The workaround as I understand from your message is to choose a dimension that makes sense for me. For this particular screen (24.3x19cm) I may choose 2430x1900. But on the other hand, I want to be able to check if the lines are 1px width (2430/1024=2.37). So either all measurements must be based on pixels or length.

                     

                    My question is: how illustrator calculates these measures? Maybe I can still have a 1024x768 artboard which (when I choose "cm" on the rulers) is shown as 24.3x19cm. If I was using a standard screen (72 DPI) it wouldn't be a problem right?

                    • 7. Re: How can I set DPI for a document in illustrator?
                      Wade_Zimmerman Community Member

                      Gee! I don't think you understood anything anyone wrote here because you are still trying to get physical length from pixel count and it doesn't work in absolute terms.

                       

                      Pixels are relative to the screen resolution. Cm mm inches points agates are definitive measurements.

                       

                      If you try to translate pixels to a physical distance it will not give you an absolute measurement.

                       

                      What you might be able to do is test this on Device Central if there is a profile for the device you are working to implement the application.

                       

                      Eve at that remember these device can zoom in and out from what is being displayed on a screen.

                       

                      I think you should serious consider changing your perspective on this issue, honestly.

                      • 8. Re: How can I set DPI for a document in illustrator?
                        JETalmage Community Member

                        Alex,

                         

                        only when I'm printing or saving the image for the web, Illustrator will ask me the actual width.

                         

                        Almost. Illustrator won't "ask you for the width." As with any program, when you export a vector graphic to a raster image, you have the opportunity to specify its resolution, in number of pixels.  Illustrator tries to "simplify" (and thereby often confuses) this process by providing different interfaces for the same thing. The so-called "Save For Web" interface is just another way to export a raster image (and other web-centric things, like slicing). The settings available (or at least the ones most prominate) differ between the straightforward Export dialog and the Save For Web dialog.

                         

                        My question is: how illustrator calculates these measures?

                         

                        Again: When Illustrator's rulers are set to "Pixels," they are really set to points. A point measures 1/72 inch. So Illustrator assumes a "pixel" is scaled to measure 1/72 inch, even though it may not be in a particular raster image object you have on the page.

                         

                        But when you export as a raster image (in other words, rasterize the artwork), you don't care what those pixels are scaled to due to the actual, physical, hardware dimensions of the device's monitor pixels (so-many centimeters by so-many centimeters). Regardless of whether the device's hardware pixels are gigantic or microscopic, you just care how many of them there are. So long as you export your finished artwork rasterized to that number of pixels, it will effectively be scaled (in terms of actual measure) by whatever device it is displayed on, becasue the device is going to "turn on" a monitor pixel for each pixel in your image.

                         

                        In other words, when designing purely for electronic displays (as opposed to printing), forget all about PPI, or DPI, which are nothing but scale factors, and forget about the actual measure (centimeters x centimeters, inches by inches) of the monitor.

                         

                        If I display your 1024 x 768 image in a web browser on my 15-inch-diagonal Toshiba laptop, your image is going to occupy 1024 x 768 of my monitor's pixels.

                         

                        If I display your 1024 x 768 image in a web browser on my 10-inch-diagonal Acer netbook, your image is going to occupy 1024 x 768 of my monitor's pixels, and it will display at a smaller actual size than it does on my Toshiba, because the Acer's monitor pixels are smaller than the Toshiba's monitor pixels.

                         

                        But even though the image's actual measure is smaller on the Acer, and even though your image occupies the exact same number of monitor pixels on both the Acer and the Toshiba, I will have to do some scrolling on the Acer because its monitor has fewer hardware pixels.

                         

                        So if I'm designing images to fit neatly on my Acer without the need for scrolling, I care about its screen size in terms of number of hardware pixels, not in terms of actual measure (centimeters or inches).

                         

                        I want to be able to set the lines and curves in terms of pixels.

                         

                        Because Illustrator considers a pixel to be a particular measure (1/72 inch), work with your rulers set to either the bogus PIxels or to Points (which, in Illustrator, is the same thing). Forget about the dimensions of a device screen. It doesn't matter.

                         

                        If you want to also spec type in terms of "pixels" you can also (pointlessly) set your General Prefs to use the bogus Pixles as the "Unit Of Measure". But this is pointless because in Illustrator, a so-called "Pixel" is, in fact a point already, and Points is the default UOM for type. Either way, you have to realize that any measure for type (using "Pixels" or Points) is a measure of the font's em-square, not the measure of the actual glyphs. So setting your type to "9 Pixels" doesn't mean the type characters are going to occupy 9 pixels in height.

                         

                        But you can proceed to specify line weights, box sizes, etc., etc, in terms of ruler units (bogus pixels or legitimate points).

                         

                        Alternatively, if you want, you can set your rulers to Centimeters. And then as you draw your boxes and set your stroke weights, you can specify them in terms of Points or "Pixels" by just typing "pts" or "px" after the measures you key into the various dimension fields.

                         

                        But after all this is said and done, the point you're missing is still this: All that means nothing if you don't export the resulting images to the number of pixels that you want them to occupy on the device you are designing for. In other words, you can work with your Illustrator rulers set to "Pixels" all day long; but if you then export the artwork to a raster format using a Pixels-Per-Inch setting other than 72, It won't be the right size, because Illustrator still thinks a Pixel measures one point.

                         

                        So regardless of how you have your rulers set while working, it is just simpler (and more legitimately meaningful) to export your raster images in terms of number of pixels (N pixels x n pixels), not by PPI. That brings us full-circle right back to where your question started: There is no document-wide PPI for an Illustrator file.

                         

                        But what you have to understand is this: If your design includes already-rasterized objects, the number of actual pixels included in each of those raster objects is entirely independent of whatever Illustrator's rulers say they "measure" in "Pixels". That is very important. Because if you use as part of your design a raster image that is scaled to anything other than 72 ppi, and/or that image does not align to a point-size increment of Illustrator's grid, then when you export your final product, that image is going to be re-rasterized to whatever PPI you export, based on its on-page position and the quality of that image is going to be compromized. That's why it's important to understand that "Pixels" is bogus as a unit of measure in a program like Illustrator.

                         

                        In pursuit of web- and device-centric creative markets, Adobe continues to add confusion-generating "conveniences" to Illustrator. For example, to workaround Illustrator's problematic antialiasing, version CS5 added a feature called Align To Pixel Grd which causes vertical and horizontal strokes to align to whole-"pixel" increments, to avoid antialiasing of those edges.

                         

                        There are also probably templates in your AI installation (depending on version) already set up for mobile devices, and there's the whole "Device Central" online thing, if you're inclined to use that kind of thing. So look up and read about those features.

                         

                        JET

                        • 9. Re: How can I set DPI for a document in illustrator?
                          alexstk Community Member

                          @JET

                           

                          I understand what you mean. I come from a programming background and for me the settings for DPI is a simple thing that's missing from Illustrator. Thanks to your description I understand why it's the way it is, but still I think some concepts and settings are pretty confusing in Illustrator. Many people have asked about this particular question in many forums. I hope people can find your description when they are looking for an answer: how to change the DPI in illustrator. It's impossible as of CS5 and even if it was, it wouldn't make sense because of how Illustrator is working with vector graphics under the hood.

                          • 10. Re: How can I set DPI for a document in illustrator?
                            alexstk Community Member

                            @Wade:

                             

                            I understand that these measures depend on the screen that they are being shown on.

                             

                            Let's say an object is 5 unit by 5 unit. The unit can be whatever. It doesn't matter. What I want is to have the rulers in Illustrator to show the size of this object to me in cm when I tell it what is the relation between cm and unit.

                             

                            So if each unit is 7 cm, I want the ruler in Illustrator to show that I have a 35x35cm object. I don't care if this object is actually occupying 20x20cm on my particular Philips monitor. I just want the rulers to tell me that my object is 35x35cm. From time to time I want to right-click on rulers and see things in unit that is I want to see that my object is 5x5 units. In fact for different purposes I need to know the size of my object in at least 2 different measurement units from time to time but the conversion doesn't work properly in Illustrator so I have to go with one measurement unit and do the conversion math using a calculator manually.

                             

                            Now this may sound complicated but it's pretty straightforward. In fact Illustrator is doing the math behind the scene assuming that each Pixel (or point) is 1/72 of an inch. But all I want to do is to change this 1/72 to something else (in this case 1/132).

                             

                            As I understand from your message and Jet's message, it's not possible as of Illustrator CS5. Be it an software architecture decision or just lack of feature, many people have asked about how to set the DPI of an illustrator document on the web. I asked it here on Adobe Forums hoping to find the answer. But the short answer is no: it's not possible as of CS5.

                            • 11. Re: How can I set DPI for a document in illustrator?
                              JETalmage Community Member
                              I come from a programming background and for me the settings for DPI is a simple thing that's missing from Illustrator.

                               

                              It's not "missing." It's just inappropriate for the kind of program Illustrator is. In other words, it is just as "missing" in any mainstream vector drawing program or object-based page-layout program.

                               

                              It's simple: The document is a collection of individual raster, vector, and text objects. Each raster object has its own number of pixels. So it wouldn't even make sense for a program like Illustrator to have a PPI setting for the whole document. That's why it doesn't really make sense for programs like Illustrator to pretend that "Pixels" is a unit of linear measure. (It's not just Illustrator that does this.)

                               

                              …still I think some concepts and settings are pretty confusing in Illustrator.

                               

                              Well, I'm the last person who would ever argue that with you. The program is needlessly confusing in many ways (not just regarding raster resolution) because of its often ridiculous interface.

                               

                              Aside: For just one example (and for kicks), try this one on for size: Draw a free-form polygon with some side angles anything other than 90°. Invoke the Effect>Stylize>RoundCorners command. The resulting dialog prompts you for a "radius." Now, I dare say you and I know what a radius is, and I dare say you and I and most anyone else in the world would expect the same results from that setting. Then set it and see what you get for actual results. Then tell me; by what logic would any software company have built that kind of interface for that feature? Illustrator abounds with such counter-intuitive and counterproductive nonsense.

                               

                              …how to change the DPI in illustrator. It's impossible as of CS5…

                               

                              No, it's impossible since forever. There never was a Document-wide DPI setting like you are envisioning. Again, it would be inappropriate.

                               

                              You may be confusing this with a poorly-named document resolution setting that earlier versions of Illustrator had. It's default value was 800. That was not what you are thinking of as a document DPI setting. That was Illustrator's treatment of a setting known as "flattness." Flattness has to do with how far a PostScript imaging device is "allowed" to deviate from the strictly geometric description of curved vector paths (in terms of printer spots, not raster image pixels) in order to avoid choking on the processing.

                               

                              That setting was (and is) commonly mistaken as meaning a document-level rasterization setting in the sense of a PPI setting in Photoshop. That's not at all what it was. The default "800" value was Illustrator's rather goofy way of expressing a flatness of 3. It was removed (long prior to CS5) because more powerful RIP CPUs rendered the whole issue moot for all practical purposes.

                               

                              JET

                               

                               

                               

                               

                              • 12. Re: How can I set DPI for a document in illustrator?
                                alexstk Community Member

                                @JET

                                 

                                Well I think your long answers put an end to any similar question. At least it's already at the top of my search results for this question in Google. Thank you.

                                • 13. Re: How can I set DPI for a document in illustrator?
                                  jggretton Community Member

                                  @alexstk

                                  I also have this problem, I too understand that when you design in vectors the width specified is arbitrary since it can be scaled. However, for many applications it is useful to be able to specify the mapping of mm or inches to pixels. A good example is generating rasterized images, but another would be inserting rasterized images into a vector design. As an expensive professional graphics program it is astonishing if this feature isn't there!

                                  Also these long stupid answers people are giving you are less than helpful.

                                  • 14. Re: How can I set DPI for a document in illustrator?
                                    PirateBanana Community Member

                                    Whaddayaknow. HEY ADOBE: Maybe if almost 10k have viewed this page, maybe this something important to consider! Maybe you should get the elitism stick out of your butts and realize that people have a need for a global DPI setting for their document.

                                     

                                    Here is my case, masters of Adobe, and you tell me if I am just clueless and retarded, or if what I am saying makes sense:

                                     

                                    I am making an envelope. A simple #9 envelope! However, when I went to set the appropriate size in INCHES when creating a new document, it ROUNDED THEM OFF TO THE NEAREST TWO DECIMAL POINTS. How dare you!!! Turns out IL did this because the native resolution of the doc is 72ppi - and that's that. So when I create a new doc in inches, it's forced to round that off because 8.875" in 72 PPI is like a few hundred measly pixels with a decimal point. I don't want a doc that's 8.88", I want 8.875" exactly!!!

                                     

                                    OK, I thought to myself. I will just create a document in pixel dimensions that will equal 8.875x3.875 @ 300ppi. Yay, it's all relative, right? Once I set my pixel dimensions (yes, I get it, they are not actually pixels, it's all arbitrary, etc.), I want to be able to export a file that is scaleable to whatever DPI will yield me a PDF with the EXACT dimensions I need. Not 2-decimal round-offs. So this should be possible! NOPE. No PDF option in the exports, "save as" yields me the usual PDF window which makes no mention of what the actual print dimensions of the document will be. There is literally nowhere to adjust the size of the thing, and unless I decide to use another program, I cannot rescale my document to a different inch size without conforming to their stupid 72 dpi limitation.

                                     

                                    So let us say that I want to produce, in Illustrator, an image that, when exported, will measure some several thousand (actual) pixels in height & width. I don't care about sizing of the elements within this file, so I don't need to know that some little image is 36x36 actual pixels instead of 100x100 point pixels. Let us say now that I want this image to be saved as a document of particular print dimensions of my choosing - for example, I have a high-resolution 10k x 10k pixel image I want to export as a PDF that will print at 1x1 inches on a card. I WANT TO DO THIS WITHOUT LEAVING ILLUSTRATOR.

                                     

                                    Adobe, are you really telling me this is not possible??? What am I failing to consider??

                                    • 15. Re: How can I set DPI for a document in illustrator?
                                      Larry G. Schneider MVP

                                      That the dialog box only shows two decimal points but the internal dimensions are to ten.

                                      • 16. Re: How can I set DPI for a document in illustrator?
                                        PirateBanana Community Member

                                        Aahh...that makes sense, kinda. I guess also PDFs don't really have an internal master DPI of sorts...it's basically dependent on what the images or other graphic assets are set to, and their size relative to the document determines what they look like in print? Like if a jpg was 600x600px at 600dpi, unscaled it would occupy 1 inch of your document regardless of anything else that goes on around it (e.g. an unscaled 60x60px jpg at 60dpi would likewise occupy an inch)...

                                         

                                        Also, I guess I forgot that print dimensions are not set past 2 decimal points, at least in most office/consumer settings...

                                        • 17. Re: How can I set DPI for a document in illustrator?
                                          Doug.S Community Member

                                          Excellent discussion and patient, clear answers.

                                           

                                          I know this was not the question at all; but,

                                          would this all be overcome or a 'mute question' by simply using Photoshop instead of Illustrator?

                                           

                                          Or is there more I am missing?

                                          • 18. Re: How can I set DPI for a document in illustrator?
                                            Gardien de la paix Community Member

                                            I've been looking for a way to set my Ai document resolution. I found this discussion.

                                             

                                            Indeed, from the programmer/mathematicians perspective, a vector program don't need a logic unit system, because vectors don't have units, by definition.

                                            But the users of this application are mostly designers who deal with unit systems (pixels for the web, cm/mm for print, and often a combination of both).

                                            In my case, the medium I am working on right now is a specific display. This display has a size in pixels, and in mm, and of course a resolution. I definitely need to be able to set my graphics sizes both in mm and in pixels.

                                             

                                            Again, the application's usability should not reflect the maths behind the programming, but what the users really need. It's as simple as this (otherwise we would still be using MS-DOS).

                                            Please Adobe, allow your buyers/users/customers/stakeholders to set units and resolutions in Illustrator.

                                             

                                            Thanks

                                            • 19. Re: How can I set DPI for a document in illustrator?
                                              Monika Gause MVP

                                              gardien de la paix wrote:

                                               

                                              In my case, the medium I am working on right now is a specific display. This display has a size in pixels, and in mm, and of course a resolution. I definitely need to be able to set my graphics sizes both in mm and in pixels.

                                               

                                               

                                              Then why don't you just do it?

                                              Save for web, enter the desired pixel size and there you go.

                                               

                                              Your display has a size in pixels and that's all that matters. When displaying your image, the resolution (ppi) will just happen automatically.

                                              • 20. Re: How can I set DPI for a document in illustrator?
                                                JETalmage Community Member

                                                …a vector program don't need a logic unit system…

                                                 

                                                Of course it does. And Illustrator has one. It's based on points.

                                                … because vectors don't have units, by definition.

                                                "Vectors" most certainly do have "units." The unit is necessary as a scaling factor to specify output size. The basic unit used in Illustrator is the point ( 1/72 inch). The point is an actual unit of linear measure (just as the inch, millimeter or mile is an actual unit of linear measure).

                                                 

                                                But the users of this application are mostly designers who deal with unit systems…

                                                 

                                                And that's why vector-based graphics programs exist: They empower the designer to design shapes which can be scaled to any measure (specified in terms of actual linear measure) needed.

                                                 

                                                …(pixels for the web, cm/mm for print, and often a combination of both).

                                                 

                                                And this is where you are making the fundamental error which is creating the confusion. Look at your list (pixel, centimeter, millimeter). Only two of those are units of actual, physical linear measure. The other (pixel) is not. A pixel is nothing but a color value. It has no size until you give it one. Consider the familiar term PPI. That Pixels PER INCH. The "per inch" is necessary to define the actual size of an image, because it is what defines the size of the pixels. Without the "per inch", the SIZE of the pixels remains undefined, because a pixel has no size until you assign it one.

                                                 

                                                In my case, the medium I am working on right now is a specific display. This display has a size in pixels…

                                                 

                                                No. The display you're working on has a native COUNT of pixels, not a SIZE in pixels. In all likelihood, many other displays have the exact same COUNT of pixels. Yet those displays may be as large as a 24" (diagonal) desktop monitor, or as small as an IPod Touch. The SIZE depends on the manufacture of the device.

                                                 

                                                A full-screen image has the same COUNT of pixels as the device. One image pixel (one color value) is sent to each monitor pixel, and the image is optimally displayed because no upsampling or downsampling (re-rasterization) is necessary to come up with the needed COUNT of pixels. You don't care about the SIZE of the pixels because the size will differ on different devices. You just care about the COUNT of pixels.

                                                 

                                                But programs like Illustrator display rulers which indicate the physical SIZE of the intended output, not the intended COUNT of PIXELS, because there are no pixels in a graphic defined by vector paths until it is rasterized. Rasterization occurs at the time of output. That's why the settings for the COUNT of PIXELS you desire reside in the various export dialogs for raster-based formats.

                                                 

                                                JET

                                                • 21. Re: How can I set DPI for a document in illustrator?
                                                  Gardien de la paix Community Member

                                                  Hi Jet,

                                                  Thanks for your perspicacity.

                                                  Yes, display have a count of pixels, and a size in mm. Or a size in pixels, and a count of mm. Up to you.

                                                  And I would love to spend time arguing on all these, but I can't. I understand from what you say that I don't know my job. So I guess I have to get back to work.

                                                  Can we at least agree on the following?

                                                  Illustrator does not offer a way to set document scale factors between the different unit systems (mm, points, pixels).

                                                  I believe many designers need to be able to define this, prior to document export, while defining object dimensions.

                                                  Thanks

                                                  • 22. Re: How can I set DPI for a document in illustrator?
                                                    Doug.S Community Member

                                                    Yes, display have a count of pixels, and a size in mm. Or a size in pixels, and a count of mm. Up to you."

                                                     

                                                    I agree with JET,  NO to last half of above statement . . . not up to anyone/you/me as there is a standard worldwide definitive meaning. Don't say 'on' when you mean 'off'; that is why we have definitions.

                                                     

                                                    Pixels inherently have no size, only can count them . . . except when you count how many pixels there are across a physical screen size in inches...then get 'pixels per inch' or 'inch per pixel' (or mm etc.) and then 'inch per pixel' has a size but ONLY for the device being examined and does NOT apply universally to other devices, displays, or printed images.

                                                     

                                                    mm and inches are inherently a dimension and have size AND you can count them.....but if displayed at other than 1:1, such as when zoomed-in on a display, they have little meaning (except in context) but are very useful.

                                                     

                                                    Ever try to show screen to display "actual size when printed"? Only works if you first know (input) 'pixels per inch' (or whatever units of measure you wish to use.)

                                                     

                                                    Definitions are extremely important. So are items with a name (=defined); such as the name of a tool or menu; use them wrongly and people will be confused and exchange of ideas or explanations will have little value.

                                                     

                                                    Doug.S