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  1. #1
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    Question Question on print resolution and megapixels

    I`m ready to buy my first digital camera. After doing a lot of reading about camera megapixels and print resolution or dpi, I`m getting a little confused. I`m hoping someone here can help. If I understand correctly ,if a digital photo is printed at 300 dpi ,which I`m told is pretty much the high standard, then a 5x7 photo would come out to 3 mp( 3150000 megapixels) Doing the math (5x300) x (7x300). Well, if I had a 5 mp or better camera and shot at that resolution,what woud happen to all the extra mp`s over that 3150000? Would the photo get cropped down to the 5x7 size.. Is it a waste to get over a 3mp camera if I will not be printing anything larger than that? I`ve heard that there is more detail in the higher mp cameras,but can it be used in a 4x6 or 5x7 print?
    I hope I`ve explained my question properly. As you can tell, I`m new to this and need a little help.
    Thanks, A.J.

  2. #2
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    Red face Re: Question on print resolution and megapixels

    Quote Originally Posted by A.J.
    I`m ready to buy my first digital camera. After doing a lot of reading about camera megapixels and print resolution or dpi, I`m getting a little confused. I`m hoping someone here can help. If I understand correctly ,if a digital photo is printed at 300 dpi ,which I`m told is pretty much the high standard, then a 5x7 photo would come out to 3 mp( 3150000 megapixels) Doing the math (5x300) x (7x300). Well, if I had a 5 mp or better camera and shot at that resolution,what woud happen to all the extra mp`s over that 3150000? Would the photo get cropped down to the 5x7 size.. Is it a waste to get over a 3mp camera if I will not be printing anything larger than that? I`ve heard that there is more detail in the higher mp cameras,but can it be used in a 4x6 or 5x7 print?
    I hope I`ve explained my question properly. As you can tell, I`m new to this and need a little help.
    Thanks, A.J.
    If you have a larger photo image, say it's a 5MP image, your image-processing software will take care of the "overage" for you. Suppose you print a 5X7 from a 2560X1920 image (5MP). Actually, since the 5X7 rectangle doesn't exactly fit the given pixel frame, you'd crop to something like 2560X1828 pixels. Now, you want to print the image. The image processing software feeds the printer driver software 2560/7 = 366 pixels for every inch of your photo. Now the printer itself works with, say, ink dots for inkjet printers, usually at a much higher dot rate than you've got for pixels. My Epson 2200, for example, typically prints at 1440 dots/inch. So 366 dots coming out of the image processor for every inch of the final print gets converted to ~3.93 dots/pixel as it hits the paper.

    So to answer your question, the extra pixels don't get thrown away, they just result in a higher resolution for your final print. Moreover, another important benefit for having more than 3MP for a 5X7 is to be able to crop your image for optimum composition.

    Yet another thing is, 300 pixels/inch is the resolution typically demanded by printers for generating magazine-quality copy for publication. The human eye can't typically resolve more than about 150 ppi. Therefore, one can actually print very acceptable 8X10 prints (at least to the un-aided human eyeball) even from a mere 2MP image.

    I hope that helps your understanding.
    Last edited by John_Reed; 05-29-2005 at 04:12 PM.
    Let a be your umbrella!

  3. #3
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    Quote Originally Posted by John_Reed
    If you have a larger photo image, say it's a 5MP image, your image-processing software will take care of the "overage" for you. Suppose you print a 5X7 from a 2560X1920 image (5MP). Actually, since the 5X7 rectangle doesn't exactly fit the given pixel frame, you'd crop to something like 2560X1828 pixels. Now, you want to print the image. The image processing software feeds the printer driver software 2560/7 = 366 pixels for every inch of your photo. Now the printer itself works with, say, ink dots for inkjet printers, usually at a much higher dot rate than you've got for pixels. My Epson 2200, for example, typically prints at 1440 dots/inch. So 366 dots coming out of the image processor for every inch of the final print gets converted to ~3.93 dots/pixel as it hits the paper.

    So to answer your question, the extra pixels don't get thrown away, they just result in a higher resolution for your final print. Moreover, another important benefit for having more than 3MP for a 5X7 is to be able to crop your image for optimum composition.

    Yet another thing is, 300 pixels/inch is the resolution typically demanded by printers for generating magazine-quality copy for publication. The human eye can't typically resolve more than about 150 ppi. Therefore, one can actually print very acceptable 8X10 prints (at least to the un-aided human eyeball) even from a mere 2MP image.

    I hope that helps your understanding.
    Thanks John ,that does help a lot. Would you know if the same happens if I have the prints made by an outside source like Walgreens, Ritz Camera etc.?

  4. #4
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    Thumbs up Re: Question on print resolution and megapixels

    Quote Originally Posted by A.J.
    Thanks John ,that does help a lot. Would you know if the same happens if I have the prints made by an outside source like Walgreens, Ritz Camera etc.?
    Yep, pretty much the same thing, the same principle applies wherever you print.
    Let a be your umbrella!

  5. #5
    Join Date
    Jan 2005
    Location
    Japan
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    1,068
    Quote Originally Posted by A.J.
    I`m ready to buy my first digital camera. After doing a lot of reading about camera megapixels and print resolution or dpi, I`m getting a little confused. . . . .I hope I`ve explained my question properly. As you can tell, I`m new to this and need a little help.
    An excellent article explaining these issues can be found at Coming to Terms with DPI, PPI and Size
    "...and only the stump, or fishy part of him remained."
    Green Gables: A Contemplative Companion to Fujino Township

  6. #6
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    May 2005
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    Quote Originally Posted by Norm in Fujino
    An excellent article explaining these issues can be found at Coming to Terms with DPI, PPI and Size

    Thanks Norm, A Fantastic article! I know I`ll have to read it several times though..

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