Higher DPI Means Higher Resolution (Really?)

Discussion in 'Digital Photography' started by leerkeller, Jun 12, 2013.

  1. leerkeller macrumors member

    Joined:
    Nov 1, 2011
    Location:
    Baltimore, MD
    #1
    I have been trying to get a solid understanding of the basic concepts involved in digital photo printing and thought I just about had it down. Then I came across this page by someone who is considered to be an authority on digital and print graphic design. I was trying to reconcile this info with what I had previously learned about DPI, but I am finding it hard. So I ask the question here, is the information quoted below correct. It was too large to quote, but there was a 73 post discussion in regards to the article and none of the information was questioned or invalidated....so that makes me think I am just too dense to understand...am I?

    http://www.vsellis.com/understanding-dpi-resolution-and-print-vs-web-images/

    Understanding DPI, Resolution and Print vs. Web Images
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    BY SCOTT ELLIS 78 COMMENTS
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    Why should you care about understanding DPI & Resolution? Because if you are going to print something (particularly of quality) or are ever tasked with optimizing images for the web, knowing a few basics will save you a lot of time and give you the best results.

    Alternatively, if you ever hire someone to develop print materials for you or build you a website, they’ll likely have requirements you won’t understand and not everyone is good at explaining them.

    Read on for a simple explanation of what you need to know.

    It’s important to begin with a good picture which means the highest resolution and image dimensions you can get. When it comes to source images, bigger is better, because you can go down in size but not up without losing quality.

    I use iStockPhoto.com for stock images and take a lot of my own pictures. If you are looking for resources to help you improve your own pictures take a look at Photo Nuts & Bolts.

    Definitions:

    DPI: Dot’s per inch. The number of dots or pixels in a single inch. The more dot’s the higher the quality of the picture (more resolution, more sharpness and detail,… ).

    Resolution: The easiest way I can explain resolution is to say that more resolution means an image displays more detail (or is capable of displaying more detail). Higher DPI means higher resolution. Resolution is not “size”, but it’s often confused with it because higher resolution images are often bigger, but that doesn’t necessarily have to be the case.

    Print: 300dpi is standard, sometimes 150 is acceptable but never lower, you may go higher for some situations.

    Web: 72dpi or 96dpi.

    Let’s see it in action…

    If you are sending someone images to use for print (again, that brochure you are having made) and they tell you the images are “too small” odds are the resolution wasn’t high enough. The image might look great and huge on your computer but is actually really small when printed out. To add to the confusion, your monitor resolution will also determine how big the picture appears to you when viewing it on your computer.

    A monitor set to 800×600 will show an 800 pixel wide by 600 pixel tall image as a full screen image. On a monitor that is 1600×1200 the image will only take up 1/4 the screen. You might have thought it would take up half, but it’s actually going to be 1/2 as wide and 1/2 as tall (so 1/2 times 1/2 = 1/4). Long story short, the image will look much smaller on that screen even though the image is the same size.

    Here are a couple of quick examples to show you the difference, no matter what your monitor resolution, it’s all relative!

    The first example below has a lot of detail and is at 300dpi (even though the web is 72dpi this works for our purposes)

    The second example is at 72dpi but scaled up to the same size so you can see the difference in detail. The actual image would be about 1/4 the size when you go from 300dpi to 72dpi, but at the same height and width is where you can actually see the difference.


    300dpi example

    72dpi example


    Hopefully this has helped you get a little clearer on the differences between DPI, resolution and why if you have someone do something for you in print there will be different requirements than for the web. It’s also why that digital camera with higher megapixels takes better pictures than one with lower (lenses and other factors being equal), because it gives you more resolution to capture more detail.

    Another important note about monitors, even though 72dpi is standard for the web, monitors have slightly different resolutions depending how you have the monitor set and how big the monitor is. For example, a 19″ monitor set to 1024×768 will show 70ppi (pixels per inch, monitors use pixels which are square not round but pixels and dots for the sake of this conversation are otherwise analogous). By comparison, a 19″ monitor set to 1280×1024 will have a resolution of 87ppx which means you fit more on the screen and get more detail, but everything looks smaller.

    Side bar: image files with higher resolution (more dpi) will also have a bigger file size because they contain more data. Start with the biggest images you can but when putting images on the web they should be set to 72dpi, it’ll save you a ton of bandwidth and they’ll load faster. Yes, they’ll be smaller than the original but should in most cases be plenty big because of monitor resolution (ppi) sizes.

    One last thing, don’t confuse “image size” with “file size.” Image size refers to the dimensions of the image while file size is how much space the image takes up on a hard drive (kilobytes or megabytes).

    Any more questions on DPI, PPI, Resolution? Ask in the comments and we’ll try to clarify.
     
  2. Hankster macrumors 68020

    Hankster

    Joined:
    Jan 30, 2008
    Location:
    Washington DC
    #2
    I worked in graphic design and web development for a long time. Computer graphics and print graphics are two different worlds. I'll give you the Cliff Notes.

    From a digital and print perspective this is what's important. DPI (dots per inch) is how many dots of any color there is to construct an image. The more dots within a square inch the clearer the image. The less dots within a square inch the less clear the image.

    The media is important. Computer monitors can only display so many DPI. The standard for all web images is 72 DPI. Print on the other hand is another animal. A good quality image on paper requires 300 DPI (very good image has 600). A very simple visual way to understand this is to create a new image in PhotoShop at 72 DPI. Drag in an image and see how it looks on the computer, then print it out. Now, create a new image in PhotoShop at 300 DPI. Drag in the same image and see how much different it looks on the computer, then print it out.

    To make it very simple just remember this: If the image is for the web it's 72 DPI. If the image is for print it should be at least 300 DPI.
     
  3. Laird Knox macrumors 68000

    Joined:
    Jun 18, 2010
    #3
    Short answer is set your image's print size to what you want without re-sampling. If the DPI value is less than say 150 then you won't get a great print. If it is over 300 then great but don't re-sample it to 300 unless required by the printer or due to size of the resulting file.

    Keep all your pixels or posterity!
     
  4. swordio777 macrumors 6502

    Joined:
    Apr 3, 2013
    Location:
    Scotland, UK
    #4
    Yes - the information in that article is correct. However the image comparison section is written in a way which may seem a little confusing.

    It's important to realise that the image comparison is really a hypothetical example of printing, albeit shown on-screen. He is certainly not saying that both images are identical, but that one has an exif tag of 300DPI and the other has an exif tag of 72DPI.

    Understand that he is not referring to exif tags at any point in this article. When he lists the necessary print & web DPI under the definitions section he's talking about the necessary image resolution.

    For example, imagine you have a photograph that you'd like to appear 3 inches wide on your computer monitor. If your monitor has 72DPI (this is fixed - you can't change the size of the pixels on your monitor) then that image only needs to be 216 pixels wide to display clearly.
    However if you wanted to print the same image so it's 3 inches wide on a page, then it would need to be 900 pixels wide to print clearly. If you tried to print out the 216 pixel image then it would appear very low quality in print. This is what the example in the blog post was showing.

    This site goes into detail and is definitely worth a read:
    http://www.rideau-info.com/photos/mythdpi.html

    Hope that helps.
     
  5. MacCruiskeen macrumors 6502

    Joined:
    Nov 9, 2011
    #5
    It's confusing because what that article is really about is the resolution of display devices, not images as such. If you have a photo that's 2k x 3k pixels out of your camera, the display device doesn't change the detail of the image, just the size at which they are displayed.
     

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