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  1. #1
    Join Date
    Jan 2007
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    4

    ?'s About DPI, Printing, and Reproduction

    Hello there! New to this forum (as you can see by my post count). I stumbled onto the main site while after doing a search for my camera (Sony Cyber-Shot 8.1 DSC-N).

    I have a problem that I assumed would of been solved with a higher Mega Pixel camera. After going through my owner's manual, as well as searching page, after page of information on the net, and even searching this forum, I can't seem to find anything relating to my specific problem (I'm sure I am looking in ALL the wrong places ).

    My problem is I can't seem to produce photos over 72 DPI. I've been told by several print companies as well as our web designer, that if we intend on using our photos in advertisements, flyers, etc., that the pictures need to be a minimum of 300 DPI or higher.

    For Example: The Dimensions of the photos will be 3264x2448 But when I right click the image, and check the properties, the vertical/horizontal resolution will only be 72 DPI

    So, two things:

    1. Is there a way to convert my existing pictures from 72 DPI to 300 DPI or higher?

    2. How can I make my camera shoot 300 DPI+ ???


    Any help and/or insight into this situation would be greatly appreciated. Thanks in advance!


    -Jewels
    Last edited by DeVus32v; 01-10-2007 at 05:48 PM.

  2. #2
    Join Date
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    That 72dpi thing is just an arbitary default in the camera.

    1. You can always assign a different dpi when you go to create a file for printing.

    2. There's no such things as making a camera shoot at a certain dpi - dpi only applies to printed media.
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  3. #3
    Join Date
    Oct 2006
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    756
    dpi is "dots per inch", and reading that literally is all you really need to know. To print 300dpi, you need 300 (linear) pixels for every inch in your output. So, your 3264x2448 photos printed at 10.88"x8.16" will be 300 dpi.

    The value you're seeing in the photo properties is just a "hint" to software, and not really used for anything at all. It's 72 because that is (or used to be) a typical pixels-per-inch value for monitors -- which is essentially the same as dpi except on the screen.

  4. #4
    Join Date
    Jan 2007
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    4
    Well thank you very much for the responses.


    After searching with different keywords last night I stumbled upon a thread from November 06. What particularly interested me was a post made by timmciglobal on a basic formula for calculating printed DPI: http://www.dcresource.com/forums/sho...65&postcount=2

    So, let me see if I have this right then. There isn’t exactly a “This picture has a DPI of (x)” because a image’s DPI will vary depending on what size you are attempting to print out. Correct?

    So, for example, with our old Sony CyberShot DCS-S85 4.1 MegaPixel camera I shot this photo here: http://www.mustangmods.com/ims/u/74/2366/134226.jpg It is 2272x1704.

    By using the above formula, if I wanted to print that picture in a 4x6 ad, the DPI would be approximately 400. And if I wanted to print an 8x10 version of the same photo, the DPI would be 220.

    So am I close or have I totally miss the mark again? Ha ha

  5. #5
    Join Date
    Oct 2006
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    756
    Yes, that's basically it.

    However, the camera produces images where each pixel is square. The formula in the link you gave assumes printing at the same aspect ratio as the original image -- keeping the square pixels without distortion. For your example, 2272 / 1704 is 1.33, but the print size is 6 / 4 = 1.5. So, you need to crop the image to 2272x1514 (or 2256x1504 to keep everything even numbers and divisible by 8, which is preferable for JPEG files for technical reasons), or else print at 5.33x4.

    Assuming square pixels and a constant aspect ratio -- which you definitely want -- you can reduce the equation to simply doing the division on either side. With the cropped image example above, the long side is 2256 dots per 6 six inches = 376 dpi, and the short side is 1504 dots per 4 inches = also 376 dpi.

    8x10 is yet another ratio (1.25), and since it's closer to your original 1.33, you have to do less cropping -- you can make it 2240x1792. So, 2240 dots per 10 inches is so easy you can do it without thinking: 224 dpi. And you can double check by dividing the number of pixels on the short side by the length of the short side to make sure you get the same number.

  6. #6
    Join Date
    Jan 2007
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    Quote Originally Posted by mattdm View Post
    Yes, that's basically it.

    However, the camera produces images where each pixel is square. The formula in the link you gave assumes printing at the same aspect ratio as the original image -- keeping the square pixels without distortion. For your example, 2272 / 1704 is 1.33, but the print size is 6 / 4 = 1.5. So, you need to crop the image to 2272x1514 (or 2256x1504 to keep everything even numbers and divisible by 8, which is preferable for JPEG files for technical reasons), or else print at 5.33x4.

    Assuming square pixels and a constant aspect ratio -- which you definitely want -- you can reduce the equation to simply doing the division on either side. With the cropped image example above, the long side is 2256 dots per 6 six inches = 376 dpi, and the short side is 1504 dots per 4 inches = also 376 dpi.

    8x10 is yet another ratio (1.25), and since it's closer to your original 1.33, you have to do less cropping -- you can make it 2240x1792. So, 2240 dots per 10 inches is so easy you can do it without thinking: 224 dpi. And you can double check by dividing the number of pixels on the short side by the length of the short side to make sure you get the same number.
    Whew.......this is a lot more complicated that I thought it was. (ha ha)


    Ok, well if I understand what you've said here, I should be able to crop the photo to 2256x1504 and maintain a decent DPI for printing a 4x6 image. I have some freebie software that came with our HP printer. In the program it give me a scaling tool where I can increase/decrease the pixels of the image (either by percentage or manually entering the desired number of pixels). However, when if you select the scaling tool a popup window opens that says

    "This tool will not change the size of your image on the screen or on the printed page. It will only change the file size when saving the file"

    Would using the scaling tool give me the desired image size that you suggested of 2256x1054 to print a 300+ DPI image on a 4x6 card? Or should I be using something else?



    I don't normally get this "involved" with this aspect of the ad design. I usually forward all the documents to a production department with sketch as to what I want. But we've been running into a lot of the same problems when it comes to submitting images for print and having them come back as "not usable." So, I was hoping to better understand not only WHY our photos weren't usably and HOW to prevent this problem from happening in the future.



    On my Sony CyberShot 8.1 MegaPixel it gives me several different image size options. 8M, 3:2, 5M, 3M, 1M, VGA, and 16:9

    What setting should I be shooting at to obtain the maximum number of pixels as possible?




    I really appreciate your time and effort.

  7. #7
    Join Date
    Oct 2006
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    756
    Quote Originally Posted by DeVus32v View Post
    Whew.......this is a lot more complicated that I thought it was. (ha ha)
    Nah, it's actually simpler. I'm just overexplaining.

    Ok, well if I understand what you've said here, I should be able to crop the photo to 2256x1504 and maintain a decent DPI for printing a 4x6 image.
    Yes. And you can do it the other way around: 6 inches at 300 dots per inch each is 1800, and 4 inches at 300 dpi is 1200. So you need 1800x1200 or bigger.

    I have some freebie software that came with our HP printer. In the program it give me a scaling tool where I can increase/decrease the pixels of the image (either by percentage or manually entering the desired number of pixels).
    Unlike in bad movies, you can't just add more detail in software. It's got to be in the original image. If you take a 3000x2000 image and scale it to 30,000x20,000, it still really only has the detail of 3000x2000, and you should use that in your calculations.

    On the other hand, if you reduce the number of pixels, you're throwing away information, so you should use the new smaller size. (I.e. don't do that.)

    However, when if you select the scaling tool a popup window opens that says

    "This tool will not change the size of your image on the screen or on the printed page. It will only change the file size when saving the file"
    I'm not sure what it's talking about there. That doesn't really make any sense.

    Would using the scaling tool give me the desired image size that you suggested of 2256x1054 to print a 300+ DPI image on a 4x6 card? Or should I be using something else?
    A camera with more pixels. That said, for many output formats, 150-200dpi is really quite decent, especially for color photographs which don't have hard diagonal lines. (It's worse for line art, for example.)

    On my Sony CyberShot 8.1 MegaPixel it gives me several different image size options. 8M, 3:2, 5M, 3M, 1M, VGA, and 16:9

    What setting should I be shooting at to obtain the maximum number of pixels as possible?
    8M -- the largest. That'll give you the full 3264x2448. The 3:2 mode simply does the cropping I mentioned before in-camera, giving you 3264x2176 -- no reason to use this unless you always and only print in 3:2 ratio formats (like 4x6, 6x9, etc.). All the rest are just shrunken in-camera.

    You can easily figure out the biggest print size this will give you simply by dividing the number of pixels (each pixel is an "input dot") by the desired dpi (the output dots per inch) -- the reverse of the calculation I was showing. So, 3264x2448 is good for 300dpi up to the 10.88"x8.16" mentioned in my first post.

    Note that this is pretty near the highest resolution available from any reasonably affordable camera -- even the 10 megapixel models would only increase the 300dpi output to about 12.16"x9.12" -- slightly more than an inch one way, slightly less than an inch the other. If you're printing larger than that, in the real world, you have to settle for less than 300dpi.

  8. #8
    Join Date
    May 2006
    Location
    Kitchener, ONT, Canada
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    Photoshop (and other tools too) have some built in functions to increase the resolution of photographs if required. They are not perfect of course, but if you MUST get a pic larger, then can do a decent job.
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  9. #9
    Join Date
    Oct 2006
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    Quote Originally Posted by dustyporch View Post
    Photoshop (and other tools too) have some built in functions to increase the resolution of photographs if required. They are not perfect of course, but if you MUST get a pic larger, then can do a decent job.
    They're not *really* increasing the resolution -- they're just making up pixels that logically might go where the missing data is. This is exactly what happens if you send an image that's only big enough to print at 200dpi at the requested size to a printer with a real resolution of 300dpi. But, it's impossible later to tell which pixels are real and which are interpolated, so you've actually reduced the quality of the image.

    Photoshop has pretty good algorithms for this -- probably the best you'll find -- but the printer has an advantage of knowing exactly its own characteristics, and it's probably best to leave it for that point. Or, at least, let the production people worry about that.

  10. #10
    Join Date
    Jan 2007
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    4
    Wow, well thank you very much for all the information. I'm still thoroughly confused (in general and on this subject, lol), but I think I have a better idea of why my older images won't work and how I can get my future images to work better for me.

    It sounds like the best I am ever going to expect any of our cameras to print out is something slightly less than an 8.5x11 sheet of paper. For the money that a more powerful camera costs and the frequency of use, it would make more sense for me to hire a photographer to go out and shoot a job for me.

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