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Thread: For those who wrongly believe that "dpi" is the resolution of a digital image

  1. #1
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    Default For those who wrongly believe that "dpi" is the resolution of a digital image

    check out the faq here:
    http://www.cs.duke.edu/~parr/photography/faq.html#dpi

    Think it explains pretty well. Here's an extract:

    The first thing that you need to understand about digital pictures is that they don't have an inherent DPI rating. That's right, the resolution of digital images is not measured in DPI.. Digital images are collections of pixels. The DPI of an image depends entirely on how you decide to display it or print it.
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    About time man. This DPI thing is the single most confusing concept among the starters. It took me a long time to grasp it myself.

    Regards
    CK

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    Originally posted by ckiang
    About time man. This DPI thing is the single most confusing concept among the starters. It took me a long time to grasp it myself.

    Regards
    CK
    after that is CoF hor? I realised CoF is something like dpi... but let's not rush in where angels fear to tread... LOL
    "I'm... dreaming... of a wide... angle~
    Just like the ones I used to know~"

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    Originally posted by denizenx
    after that is CoF hor? I realised CoF is something like dpi... but let's not rush in where angels fear to tread... LOL
    CoF? You talking about DoF or CoC?

    Regards
    CK

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    Originally posted by ckiang
    CoF? You talking about DoF or CoC?

    Regards
    CK
    CoC lor
    but Ruminous NandScape calls it CoF... which is the sound u hear when u think too much CoC...
    "I'm... dreaming... of a wide... angle~
    Just like the ones I used to know~"

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    Originally posted by denizenx
    CoC lor
    but Ruminous NandScape calls it CoF... which is the sound u hear when u think too much CoC...
    Too confusing!

    Regards
    CK

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    Default Re: For those who wrongly believe that "dpi" is the resolution of a digital image

    Originally posted by mpenza
    check out the faq here:
    http://www.cs.duke.edu/~parr/photography/faq.html#dpi

    Think it explains pretty well. Here's an extract:

    The first thing that you need to understand about digital pictures is that they don't have an inherent DPI rating. That's right, the resolution of digital images is not measured in DPI.. Digital images are collections of pixels. The DPI of an image depends entirely on how you decide to display it or print it.
    Thought we've sorted that out long ago

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    Default Re: Re: For those who wrongly believe that "dpi" is the resolution of a digital image

    Originally posted by jasonpgc
    Thought we've sorted that out long ago
    Well, still comes up every now and then. I think I replied those dunno how many times liao, mpenza too.

    Regards
    CK

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    DPI stands for Dots (pixels) Per Inch

    dpi * size (in inches) = pixels
    Conversely,
    size = pixels / dpi
    dpi = pixels / size

    Therefore a 2 Megapixel Camera which produces an image of 1600x1200 pixels can print an image of

    8 inch wide at 200 dpi (Magazine Quality) 8 * 200 = 1600
    5.3 inch wide at 300 dpi (High Quality Print) 5.333 * 300 = 1600

    You can use Image.Size in photoshop and uncheck 'Resample Image' and see how the inch/dpi changes in relation to each other
    Last edited by willyfoo; 7th June 2003 at 01:12 PM.

  13. #13

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    Additional Info

    Screen resolution is typically 72 dpi
    Printing from IE is 96 dpi
    Newspaper is about 100-150 dpi
    Magazine is about 200-300dpi
    Quality Deskjet Print starts from 300dpi
    LaserJet prints usually is at 300/600 dpi

    However printing photos beyond 300dpi does not show noticeable difference. (Disclaimer: your mileage may vary)

  14. #14

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    Originally posted by willyfoo
    Additional Info

    Screen resolution is typically 72 dpi
    Printing from IE is 96 dpi
    Newspaper is about 100-150 dpi
    Magazine is about 200-300dpi
    Quality Deskjet Print starts from 300dpi
    LaserJet prints usually is at 300/600 dpi

    However printing photos beyond 300dpi does not show noticeable difference. (Disclaimer: your mileage may vary)
    Actually, a magazine's photograph is nearly 600 - 3000 dpi depending on the quality of the magazine. Take a magnifying glass and look at the pictures in it and you will not even see a pixel .

    Current Laserjet printout is ranging from 300 - 1200dpi, there are even 2400 dpi printers (Mid Magazine Quality) but on the higher end.

    Deskjet has the problem of smearing (Even though they claim a quality of 2400dpi (espon)), although the technology now make it almost impossible to see with naked eyes.

    I don't know about newspaper print, never read about that before.
    Last edited by blurblock; 7th June 2003 at 09:06 PM.

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    that's surprising. do you refer to the input image resolution or the output resolution? both aren't the same.
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    Do not, I repeat, do not, confuse image resolution (expressed as PPI / PIXELS per inch) with the final printer dpi (DOTS per inch).

    The latest Epson printers run at 2880 and 57600 Dpi, but doesn't mean your image has to be at that kind of size. Going beyond 300Ppi gives no noticeable improvements. Going beyond 300Dpi on the inkjet printer DOES give noticeable improvements. But above 1440dpi on the printer gives no improvements other than to waste ink and time.*

    Regards
    CK

    * Unless you are printing B&W prints using ONLY the black ink

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    How does the DPI concept work while scanning.. If I remember most of the scanners specs say 1200x2400, 2400x2400, 4000x4000.... Doesn't it translate to pixels as well...

    Can you pros, explain that to enlighten me a bit as well...

    thanks in advance

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    hi guys,

    i am using a DOF calculator program for my ppc, and there's this option which stated resolution as lines/mm.
    litttle confused...
    is resolution commonly measured by lines/mm? or is that for film only?

    regards

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    it's been a while. up again for newcomers and anyone who needs clarification....
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    Quote Originally Posted by akdwivedi
    How does the DPI concept work while scanning.. If I remember most of the scanners specs say 1200x2400, 2400x2400, 4000x4000.... Doesn't it translate to pixels as well...

    Can you pros, explain that to enlighten me a bit as well...

    thanks in advance
    you have an input size. if you scan a 4 inch by 6 inch at 1200dpi, you get an image which is a collection of 4800x6000 pixels with no inherent dpi rating.
    Check out my wildlife pics at www.instagram.com/conrad_nature

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