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PPI, DPI, Pixel Resolution.. and Printing?

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  • #16
    Originally posted by h2k47 View Post
    @ PanToshi
    Sir, is your first question really relevant to the topic ?
    It is always relevant when pulling images from "random sites on the web". I dare say, it is always relevant. But, as you think it is not relevant to your topic, I'll wish you a Happy Thanksgiving and be on my way.
    Last edited by PanToshi; 11-22-2012, 01:41 PM. Reason: add words
    Sketching not only helps you work out good ideas, it helps you get past the bad ones.

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    • #17
      I think that some of this discussion points to the subjective nature of how much detail is needed in large-format imagery. I could scan a 35mm slide, and if I cropped, say, half of it away then enlarged the remainder to fill an entire 8.5x11-inch magazine page, it would be noticeably blurry. On the other hand, I could enlarge that same image to fill a wall and, depending on the variables involved, it might look okay.

      This wouldn't be because the photo magically became sharper, it would be because the sharpness and detail isn't necessarily expected at larger sizes — even when seen from relatively close up. In other words, it's a cognitive phenomenon.

      If a 1x1-meter lobby print is hung on a wall as a purely decorative element that gives color to the wall as people walk by, a 100-ppi image, or even lower, will likely work out just fine. Likewise, if it serves as a background image or if the photo lends itself aesthetically to less sharpness, it'll be fine.

      On the other hand, if the image is meant to be studied in a way where sharpness is either important from a communication or aesthetic standpoint, a 100-ppi resolution wall image might be noticeably too fuzzy. It will also be noticeable if that low-resolution image is in close proximity to other, higher-resolution images that are sharper. If that 1x1-meter wall image is meant to catch people's attention from, say, three or four meters away as they walk by, then draw them in for closer inspection of whatever the image is about, I'd be unlikely to be satisfied with anything less than 150 pixels per inch since I would want the image to reveal increasing detail as the viewer approached.
      Last edited by B; 11-22-2012, 01:58 PM.

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      • #18
        Originally posted by h2k47 View Post
        @ PanToshi
        Sir, is your first question really relevant to the topic ?!
        It is, because you posted:

        Originally posted by h2k47 View Post
        1- I was told to search online for photographs of famous places for printing.
        2- I searched online and found few pictures that were 4000x4000p and has 72 pixel/inch resolution as photoshop showed.
        This article came down my Twitter stream a short time ago. It's written for bloggers, but applies equally to print designers:

        http://socialmediatoday.com/lggodard...ages-your-blog

        I would especially direct your attention to reason #5:

        5. Bottom line - a license is almost always cheaper than a lawsuit:

        “The court determined that, had Dream Communications properly licensed the photo, it would have paid just under $8,000 in licensing fees. Finding that Dream Communications was liable for willful copyright infringement, the court awarded Pacific Stock statutory damages of $45,000 plus almost $7,000 in attorney fees and costs.”
        This post is brought to you by the letter E and the number 9. Those are the buttons I push to get a Twix out of the candy machine.
        "I put my heart and my soul into my work, and have lost my mind in the process."

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        • #19
          My apologies PanToshi and Happy thanksgiving to you too Pantonshi and to everyone...To answer your question: ' Yes, I have read the EULA and they are all legal wallpapers.'

          @ <b>
          I understand perfectly what you mean. It is all about the 'purpose' of an image that determines the DPI at which it will be printed at.

          It is also interesting what you said about larger images being cognitively 'perceptual-ed' as blurry images from a distance since our brains 'wants' or are 'used to' them like that. Very interesting idea.

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          • #20
            Originally posted by PrintDriver View Post
            Pixels per inch and all that Line Screen math are all fine and dandy
            Indeed. I've sent many a penguin stand (pull up stand) jobs to print with 30 ppi and they look terrific.

            Very happy with the results.

            This brings us back to "Consult with your print provider" - as mentioned many times


            But you know - the OP was confused about the whole thing - I broke down how it works and why it works - and evidently they now understand it.

            That's another satisfied GDFer

            "May your hats fly as high as your dreams"Michael Scott

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            • #21
              Yeah but he's still confused by ink dots.
              When doing large format you aren't playing with 1ink dot = 1 pixel.
              In other words, each inch of these 55.5 will be filled with 72 ink dots.
              This statement is wrong.
              There may be 72 "pixels" but you would have anywhere from 150 to 3000 "ink dots" per linear inch. What you have is 72 blocks, each representing a digital pixel block, and the print device will print those blocks as squares of color using many many hundreds of ink 'dots' per block. This is even better illustrated by taking an image up to an uninterpolated size of 4dpi for instance. You would have 4 blocks per inch, each representing one pixel but they are 1/4" square blocks of a single color. Again, each block that size would be printed using 1000s of ink dots.

              If you interpolate an image so that it is larger in an attempt to make those blocks smaller, you will only get approximations on the colors those blocks should be. Hence the artifacts you get in digital imagery when you try to enhance the resolution.

              As for <b>'s explanation of an image to draw you closer and expecting more detail as you get closer...the detail has to be in the image to begin with. You wouldn't expect to be able to output a wall mural as a single image and hope to keep the actual resolution at 150ppi at such a large scale. Well, maybe you could if the image started old school on color transparency film and was scanned in a drum scanner, but even with that, there comes a point where film grain clouds your image clarity. You could even start with a professional 35mm slide as long as the film was slow film. A 400 speed 35mm isn't even going to go to 11x17 without film grain becoming apparent, while a 100 speed 35mm might go to 48" h proportionally. There are very few digital cameras that can come close to the sharpness of the larger format CTs. They are very expensive and in most cases require a still subject (no movement) due to the long scan time required to process the image digitally. Most consumer side digital cameras don't even come close.

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              • #22
                Part of the learning curve - not really a curve more of an infinite line always increasing. You don't stop learning.

                This is the basics. I appreciate that input there I picked up a few things myself

                "May your hats fly as high as your dreams"Michael Scott

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                • #23
                  Sry for the late reply...

                  I was trying to make things easier for me by saying that each inch will contain 72 ink dots but now I understand that they are actually 72 blocks of ink and not dots.Thanks for the correction.

                  Is there some specific table that shows the amount of resolution required for a designated output that most printers follow?

                  I know PD suggested that a general number of 150 DPI which nearly translates in pixels to 11,000 ( 11000 divided by 72) which was generally good for my desired 1m x 1m poster. But what about the other sizes, or is 150 DPI, a global number?

                  Many thanks again...

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                  • #24
                    You always need to discuss image resolution with your printer. Especially in large format. The machines are all different. The media is all different. The viewing distance is key.

                    And again, you are confusing dpi with ink droplets.
                    An image that is 150ppi could have as few as 100 inkdroplets per inch. In regular press it could have as few as 60. Pixels per inch, Lines per Inch and, and Dots per inch are not the same thing.

                    A 150ppi image can be 150ppi at 36" (5400 pixels wide) or it could be 150ppi at 3.6" wide (Only 540 pixels wide). But it's not the same image. To take it one step farther, you can't take a 150ppi image at 3.6" and make it 150 @ 36". Will never happen. You could, however, dumb down a 150ppi 36" image to one that is 3.6" without too much trouble (there are exceptions). Are you tossing data. Yup. Irreversibly.

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                    • #25
                      Originally posted by PrintDriver View Post

                      And again, you are confusing dpi with ink droplets.
                      An image that is 150ppi could have as few as 100 inkdroplets per inch. In regular press it could have as few as 60. Pixels per inch, Lines per Inch and, and Dots per inch are not the same thing.
                      What are their differences?

                      Originally posted by PrintDriver View Post
                      A 150ppi image can be 150ppi at 36" (5400 pixels wide) or it could be 150ppi at 3.6" wide (Only 540 pixels wide). But it's not the same image. To take it one step farther, you can't take a 150ppi image at 3.6" and make it 150 @ 36". Will never happen. You could, however, dumb down a 150ppi 36" image to one that is 3.6" without too much trouble (there are exceptions). Are you tossing data. Yup. Irreversibly.
                      In other words, a smaller size image cannot be enlarged even if its ppi was 150. This is similar to trying to make a small image bigger which would cause loss of quality and artifacts.

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                      • #26
                        Originally posted by h2k47 View Post
                        What are their differences?
                        Read this it explains it pretty well. http://en.wikipedia.org/wiki/Halftone
                        .

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                        • #27
                          That wiki entry describes halftoning as applied to plate. While digital inkjet uses something similar, inkjet doesn't use linescreens or color angles.

                          The difference between ppi, dpi and lpi
                          ppi = pixels per inch and describes a digital image. Each pixel is a tiny square. On a monitor, there is only one size square so depending on your pixel dimensions the image will get larger or smaller but the squares always remain the same size. When translated into print, each pixel is a tiny square of a single solid color that varies depending on the size of the image. The squares change size. If your image is 150ppi there are 150 squares per linear inch. If it's 4ppi, there are only 4 squares per linear inch.

                          DPI = dots per inch in digital printing is what the print machine is capable of laying down on the media being printed. So while your image may be 4ppi and therefore is made up of single color squares that are 1/4" on a side, you may print those single color squares using a combination of CMYKcmOVG ink dots in a dot pattern as high as 1200dpi or 1200 ink dots per inch, or even more. DPI is often used interchangeably with PPI and tends to mean the same thing to most of the design world in the same way that nose tissue is called Kleenex. If in doubt, clarify.

                          LPI = Lines per inch and is used to measure a halftone grid. How many lines of halftone dots per inch. A lower number means a courser grid. This term is not generally used to signify anything in digital inkjet printing, although you do run across people who confuse it with the step resolution of a machine. Some print machines are capable of higher resolutions in the horizontal direction (across the media) than they are in the step direction (direction of feed). The same is true of digital scanners. This is why you sometimes see resolutions of scanners given as 1200x 600 for example.
                          Last edited by PrintDriver; 11-26-2012, 05:55 AM.

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                          • #28
                            Originally posted by PrintDriver View Post
                            The same is true of digital scanners. This is why you sometimes see resolutions of scanners given as 1200x 600 for example.
                            On a side note, I've increasingly seen scanner resolutions referred to as SPI or samples per inch. This, I suppose, is meant as a way of differentiating scanner resolutions from the others.

                            It might also be worth mentioning that all these designations for different types of resolutions are often treated interchangeably and inaccurately by many people — even in text books and instruction manuals. In offset printing, for example, people frequently say or write DPI when they mean LPI. Likewise, electronic pixel measurements are often referred to as DPI instead of PPI. It can all be confusing, especially when people get their terminology wrong.

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                            • #29
                              Billboard

                              Here is the information I was given..."As for the jpg for the billboard, this file needs to be (602 inches) 50.1667 feet wide by (169.3 inches) 14.11 feet high and 32 dpi. The low dpi will work because people view it from far away. Because the billboard paper tends to stretch, when you design the image, it might be wise to design it at 49 feet but with a foot of material that can be cropped on the far right. The file size will be about 500 MB so we'll either have to use dropbox or some other file transfer service to send it or else mail it on a CD."

                              I am very confused...I plan to create a digital collage using photoshop...in reality...with a higher DPI...what is the smallest size in inches I can make the image in photoshop?

                              I appreciate and look forward to any and all suggestions.

                              thank you

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                              • #30
                                Hi creegal and welcome to GDF!

                                We ask that all new members take a few minutes to read through important threads here and here. These will explain our rules, answer frequently asked questions and explain some of the long running jokes you'll run into. Enjoy your stay.
                                Sketching not only helps you work out good ideas, it helps you get past the bad ones.

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