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Thread: DPI and commecial inkjet printing of ArtRage paintings.

  1. #1
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    DPI and commecial inkjet printing of ArtRage paintings.

    There's a host of conflicting exchange in the forum re: dpi and related print output. Perhaps someone with experience in the printing industry can answer the following:

    1) In Artrage, what is the best dpi setting for building paintings that will be printed on large format commercial inkjet printers (200dpi? 300dpi? something different)?

    2) A related question, for commercial inkjet printing purposes, does it make a difference if the exported file (from ArtRage) is a jpg or png? Will the png file provde better printing quality on commercial inkjet printers?

    3) Finally, will an ArtRage painting built at, say, 150 dpi and exported as a png file successfully scale up to 300 dpi (while retaining the original dimensions) when rescaling the png file, i.e., will the scalled up version be a true 300 dpi image at the same dimenstions, or will the file, for printing purposes, be only as good as the exported 150 dpi file?

    I ask these particularly because ArtRage appears unable to handle large paintings (say 24"X36" and up) at 300 dpi - it appears to run into RAM limitations around 200 dpi and at about 24X36". So the question is, how to build large paintings in ArtRage that will assure good print quality with commercial inkjet printers?

    Any knowlegable help with these will be greatly appreciated. I know dpi questions can cause a lot of confusion, so I'm happy to clarify anything that isn't clear in the questions above. Thanks in advance for anyone who can help with this.

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    The raster image is made of pixels. You can think of DPI as of count of pixels per linear inch of the image - i.e. a 300 dpi image will have 300x300 = 90000 pixels per square inch. (For printers, the conversion is not 1:1, due to the technologies of combining pigments on paper, but it's close enough.) Think of it as the image's pixel density.

    If you stretch the image from, say, 150 dpi to 300, the image will not look better. Even while it will have, technically, four times the pixels, the amount of image information in it will still be the same as the original image - the quality will not be improved. You have used up more pixels, but you actually reduced the pixel *density* by the factor of four.

    DPI setting stored in image files is just a hint for the printer. It is used for getting real-world dimensions of the image from its pixel dimensions. If you specify half the DPI, you tell the printer that your image is to be printed at double size. You can specify in your image that it is at 1 dpi and it will cover a square furlong, but each pixel will be an inch wide - unless you add enough pixels to cover a square furlong more densely.

    How many dpi is enough depends on the image's intended viewing distance. 300 dpi is about the point where the color image begins to look smooth to a human eye at the distance of 12 inches or so. For black-and-white images 600 dpi is the minimum, and for especially fine lines, 1200 may be needed. On the other hand, if you want a poster that would be looked at from at least five feet, you can safely use a 72 dpi original and not really lose quality. And billboards are often printed with dots you could pick up with your fingers. In fact, if you intend to make a big poster, it is simply a waste to paint the original at 300dpi - no one will look that closely at it to discern detail that small.

    So: fine art color prints to hang on your wall, ideally, need at least 100 dpi, as a rule of thumb. Smaller color prints that you take in your hands to look at, ideally, need 300. But you can blow up a color picture that's A4 at 300 dpi up to A2 without appreciable loss of quality - that's about 72 dpi. In many cases you can blow it up to A1, if it does not rely on fine linework.

    You can experiment yourself - print a fragment of the same image at different dpi and check at which distance from it you'll cease seeing the dots and see a continuous image. That will give you an idea of which pixel density you need for each case.


    With modern technology it is best to just give the printer your original image at its original resolution and let them handle the stretching and such. They'll have the algorithms that suit their hardware precisely, and will get a much better result than you can achieve at home. (Same goes for color matching; nowadays you are typically better off if you give the printer the RGB original, instead of trying to convert it to CMYK yourself - especially since modern processes can use more than four colors.)



    As for JPG vs PNG format: JPG is a format intended for viewing. It achieves high compression by rearranging pixels in your original image in ways that are highly compressible but still look *enough* like your image to human *eye*. The key points are "enough" and "eye". JPG compression alters the image and produces artifacts which may not be apparent to your eye but may get very noticeable if you print the image, enlarge it, etc. These compression artifacts are most apparent at high compression ratios and around the edges, they look like halos or oversharpening effects, and in worst cases they replace color gradations with vertical or horizontal linear gradients. Repeatedly recompressing the image (i.e. saving as JPG then loading then saving it as JPG as you work) usually makes them much worse.

    All this means that you should NOT use JPG images for work or storage, as the repeated compression will degrade the quality. Use lossless compression like PNG, PSD, TIFF with LZW compression. You can give a good quality JPG file (exported directnly from the lossless original and at low ratio) to a printer, there will be no appreciable degradation. But do not use it for work. Use JPG for exporting the end product only, and at low compression ratio - the ratio should be at least 80-85 as Photoshop counts it.
    Last edited by arenhaus; 02-13-2009 at 10:28 PM.

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    Much thanks and Clarifying Question

    Arenhaus, thank you for putting so much effort and thoughtfulness into tackling my question.
    It is extremely helpful.
    For my purposes, I have the following take-away, and I'd like to see if you concur.
    Following is my take-away:

    I am making paintings for output at commercial inkjet printers at 36" X 24" or larger.
    They will hang on walls for viewing at normal distances. If I
    1) build my paintings in ArtRage at 150 dpi (or 200 dpi?),
    2) ensure my dpi and canvas dimensions have been properly set in ArtRage from the beginning, and
    3) export to PNG without any rescaling
    I can safely let my commercial inkjet printer use the exported PNG file and the image will look fine to the average viewer?

    Is this a correct assumption to draw from your input, or have I misinterpreted your salient points?

    Thanks again. I very much appreciate the thoughtfulness and thoroughness of your previous response.

    Best, Byron

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    Your assumption looks correct to me. Provided that your printer isn't clueless, of course, then all bets are off.

    In any case, it is wise to do one test print first to see how your printers will handle it, so you don't get surprises in the production run. Get a picture printed and see if there are any color discrepancies, artifacts, visible pixels and such.
    Last edited by arenhaus; 02-15-2009 at 07:00 AM.

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    Thanks again Arenhaus

    Arenhaus, thanks again. You've been very generous with your help. Very much appreciated.
    - Best, Byron

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    I just found this thread. Excellent information arenhaus! Thank you!
    "The significance is hiding in the insignificant. Appreciate everything."
    Eckhart Tolle

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    Sticking this thread as a resource for DPI discussion.

    Other related discussions which may be of use:

    http://www2.ambientdesign.com/forums...ad.php?t=18966
    Dave
    Resident Bug-Hunter
    Ambient Design

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    I am very glad this was stikied, finally a definitive answer on printing sizes

    Thanks very much for your time arenhaus, very much appreciated
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    If you intend to print your work, read the link below. I find that most people - even people who work in the industry - don't understand DPI. This article explains it perfectly - it even goes into detail about the "horrible DPI error" that causes people to misunderstand what DPI is (I just wish I'd found this article before I made innumerable posts on the subject )

    The key point is that DPI has not effect whatsoever on digital image quality, dimension or size.

    http://www.rideau-info.com/photos/mythdpi.html

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    Simon - The DPI count is a device's dot pitch. It has nothing per se to do with its pixel number, so 800x600 at 72 dpi and 800x600 at 300 dpi are the same image. The only case you'll notice the difference is if you try to print it at 1:1 scale - you'll get a stretched 72 dpi image and a postage-stamp-size 300 dpi image. A computer display will still show it as 800x600.

    Now, if you are talking about a 8"x10" image at 72 dpi and 300 dpi, that's a big difference, since it's dots per inch, not a fixed number of pixels. One will be 576x720 pixels, the other 2400x3000. The second image will be of a much higher resolution. So in linear measurements, DPI count is important.


    Matthew - In mid-1980s I was still in high school, so I can't give you any first-hand experience on that. However, the 300 dpi figure is the optimum for printing continuous tonal images like photographs or paintings. For type or black/white line art, 300 dpi is inadequate - the minimum for those is 1200 dpi, and the more the better. That's not so far from your 1750 dpi figure. You mention that it had to be "camera ready" and "typeset" - well, if it includes type, it has to be at least 1200 dpi or you'll get muddy type.

    Nowadays print shops still like the PDF format, but they will print TIFFs just as well, and even JPEG images of sufficiently high quality. PDF is still de facto standard because it can combine text with images, and you should leave the rendering of text to the printer's equipment whenever possible.
    If you only have an image, a TIFF file should be all right.

    (Yes, LZW is lossless compression.)

    The rules of thumb would be: prepare/scan/export your tonal images at 300 dpi RGB, line art at 1200dpi monochrome, and if it combines images and text, prepare an Acrobat PDF document with embedded typefaces and full images (optimize the PDF for print, not for screen, and forbid it to resample images). And unless the print shop requires it, don't export your own CMYK, let them do it.

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