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Thread: DPI does not mean Quality!

  1. #1
    Join Date
    Jul 2006
    Posts
    93

    DPI does not mean Quality!

    I wonder how it came to be that the term "dpi" has become such a confusion for so many people. I honestly blame Adobe for this, because even at the inception of PostScript in the mid-80s, displays were not always 72 dpi, they defined that number for other unrelated and technically inaccurate reasons.

    If it's a digital image, there is no "dpi." It stands for Dots Per Inch. In most cases dots means pixels. Digital images all by themselves have no inches, only pixels. It's only when you know how many inches you're talking about, that the term "dpi" could possibly be meaningful. The dpi number attached to a file has nothing to do with its quality at all.

    If you have a 10x10 inch piece of paper, THEN you can consider how many pixels to put on it. 300dpi works out to 3000x3000 pixels. Easy math. 150dpi works out to 1500x1500 pixels. Easy math.

    If your target is the screen, forget about dpi entirely. One image has been saved with 3 dpi. The second image has been saved as 3000 dpi. See any difference in quality? The dpi does not mean quality.

    If I printed these images from a graphics program, and the graphics program didn't tell the printer any special sizing information (which is exceedingly rare), then the 3dpi image would measure over 100" wide, and the 3000dpi would measure just over 1" wide. If the program told the printer what to do explicitly, like most applications do, then they'd print the same size, as your web browser is showing you.

    Both were set with the same JPEG compression settings, so even though the "dpi" were saved differently, they both come out to the same file size too. The dpi does not indicate quality!
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  2. #2
    Join Date
    Dec 2006
    Location
    Netherlands
    Posts
    78
    The thing is that many artists sell their work in print form. This is why they want ArtRage to be able to specify the DPI, so they don't have to transfer it to another program, such as Photoshop, to specify the DPI at which the file is saved.

  3. #3
    Join Date
    Jul 2006
    Posts
    93
    But it's not the DPI that means quality. It's the number of pixels. If you have 3000x3000 pixels, and tell it to print over 10x10 inches, the result will be the same no matter WHAT the file's dpi record says.

    Since almost all printers, print applications, or printing service bureaus actually use processes which IGNORE the dpi record in the file, it's really annoying how confused people get about how much the dpi record in the file matters. It matters not.

    You're right in that you have to make enough pixels to fill the space to avoid a "blocky" look. That's a matter of pixels. Asking an application to mark your files with a certain dpi number just propagates the confusion about it.
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  4. #4
    Join Date
    Jul 2006
    Posts
    93
    Sweedie, I think you and I are both thorougly familiar with the concepts involved. We even agree in general: on the physical media (where there's inches to measure), the dot/pixel density is important.

    What raises my hackles is that the typical Adobe-infected user comes away from their horrible user interface thinking that if a file is not marked as 300 dpi, then the quality is poor or the artist didn't set things up properly.

    If you only have 800x600 pixels, there's no way you are going to fill a poster, because the pixel density is too low. This has nothing to do with the dpi settings but with the actual physical dots-to-media density. ArtRage says it works in 72dpi, for example, which causes many newcomers plenty of consternation because they heard somewhere that if it isn't 300dpi it will suck.

    Ask ArtRage for more pixels, export to PSD, and then tell it to fill the page. It doesn't matter if ArtRage says something like 72dpi in the original file, because as I've mentioned, the printer itself doesn't care what's in the file. The application (in "Page Setup" or "Print Preview" or other similar features) will decide the final dots-per-inch and it can be completely unrelated to the original application, such as ArtRage.

    Again, I'm not arguing with you-- I just think that the way that Adobe presents their dialogs has poisoned the minds of many in the industry who haven't actually thought about the math involved.

    There are lots of photographers and publishers who fight the same battle: "my $4000 digital camera says its JPEGs are 120 dpi, and the publisher won't accept those, but my friend's camera with the SAME megapixels marks them with 300dpi and the publisher takes those no problem." What is 300dpi to a camera? Nothing. The photosites are smaller than a thousandth of an inch. It depends on your chosen print size, since the number of pixels doesn't change, and the print size is up to you and your application, not the camera at all.
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