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How can I set DPI for a document in illustrator?

Jul 8, 2011 1:43 AM

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)

  • Currently Being Moderated
    Jul 8, 2011 4:00 AM   in reply to alexstk

    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.

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  • Currently Being Moderated
    Jul 8, 2011 5:33 AM   in reply to alexstk

    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.



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  • Currently Being Moderated
    Jul 9, 2011 9:53 AM   in reply to alexstk

    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.

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  • Currently Being Moderated
    Jul 9, 2011 10:07 AM   in reply to alexstk
    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.



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  • Currently Being Moderated
    Jul 9, 2011 2:40 PM   in reply to alexstk

    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.

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  • Currently Being Moderated
    Jul 10, 2011 8:32 AM   in reply to alexstk



    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.



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  • Currently Being Moderated
    Jul 10, 2011 11:07 AM   in reply to alexstk
    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.







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  • Currently Being Moderated
    Nov 29, 2012 9:45 AM   in reply to 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.

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  • Currently Being Moderated
    Apr 18, 2013 2:35 PM   in reply to alexstk

    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??

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  • Currently Being Moderated
    Apr 18, 2013 3:00 PM   in reply to PirateBanana

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

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    Apr 18, 2013 3:15 PM   in reply to Larry G. Schneider

    Aahh...that makes sense, kinda. I guess also PDFs don't really have an internal master DPI of'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...

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  • Currently Being Moderated
    Apr 20, 2013 7:29 AM   in reply to PirateBanana

    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?

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