 Cindy Sj |
dpi for a publication...is that camera or printer? a friend has asked me to shoot a picture or 2 of her products for an article in a magazine...she needs 300dpi.... ok, I'm a novice. I know how many megapixels my camera has, but dpi? isn't that dots per inch? Is that controlled by the printer that a photo is printed out on or is it something I can do on a Nikon d70s or d80? Pictures due by 11/29, so any quick help to help me understand will be greatly appreciated!! [=
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robert G. Fately |
Cindy, pixels and resolution and dpi are terms that confuse a lot of folks. Hopefully I can help. The camera you have records images on a chip that is basically a very fine screen or matrix - perhaps 3000 columns wide by 2000 rows tall. That 3000x2000 effectively equates to 6,000,000 individual cells; these are called "picture elements" or "pixels". Be aware that this is purely for example purposes; the real technology underneath is a bit more complex but for our purpose this will do. Meanwhile, there's the concept of resolution - how many distinguishable dots per inch can be discerned. Different output devices have different native resolutions - computer screens typically have something around 72 to 85 ppi (points per inch), while printers usually hover around the 300 ppi your friend requested (other printers have higher resolution, yet others somewhat lower). Okay, so let's just say you take an image that fills the frame - the full 6 megapixels. The image file, then, is 2000 pixels on one edge, right? If you load this image into Photoshop, it will likely initially "assume" a resolution of 72 ppi to calculate an image size of (2000/72=) 27.77" high by (3000/72=) 41.67" wide. That's just math. In Photoshop (or any post-production image editing program)you can resize the image - go to that window and don't change anything but the resolution to 300 ppi and now you'll see the calculated size is 6.67" x 10". Make sense? Finally, let's say you need a larger image than that - not a problem. Digital images are particularly capable of upsizing - again, your Photoshop-like program should have such a function. So you could bump that image up to 8x12", say, still at 300 ppi - the program will interpolate and add more pixels to make the entire image 2400x3600 pixels. So we started with a 2000x3000 pixel image and resized and re-resolved it to a 2400x3600 image at 300 ppi. Does that help?
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Samantha L. Dean |
Something to add. LPI is lines per inch. That is what print press operators refer to. Most newpaper printers print at about 130 lpi while color product is usually printed at 150-200 lpi. When you change your image resolution using photoshop be sure to uncheck the resample image box first. NEVER manually change your resolution. When you resample the image, change height and width and the resolution will change to compensate. I work in the art / marketing department of a major gift bag design company. We require all our files to be at least 8 x 10 at 300dpi in order to go to print. Hope that helps!
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Mark Feldstein |
The commercial printing process is both an art and a science. DPI refers to the line screen that printers use in the plating process to apply ink to the paper on the press. Newspapers use about a 60 DPI line screen whereas high end magazines use upward towards 300. If you take something like an 8X loupe and compare the printing of a b&w newspaper photo to a 4 color magazine photo, you'll see the ink dot pattern much smaller and tighter in the magazine. That in turn, makes for more clarity or sharpness in the final printed image. The resolution or clarity in the commercial printing process is also based on the type of paper used and the various coatings applied to the paper when it's manufactured and also coatings applied, like varnish after it's printed.
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Mark Feldstein |
BTW Cindy, in terms of professional photographers working with commercial printers, part of that craft involves knowing how to shoot for a particular printers window within whatever f-stop range that printer is going to work in. That means knowing how to expose your images for adequate detail in shadow areas that can be recorded in the printing process and also knowing how to shoot highlights so they're not blown out and the press can handle them as well. It's basically a balancing act that also varies according to whether you're working in b&w or color. In the older days, knowing how to push/pull film, for example, to add or decrease contrast of a transparency, can make or break a press run. Sometimes these days, people trying to fix their work in PS adjusting and playing with contrast and balance, etc., just creates a nightmare for the printers. An interesting problem to be sure. Next time you look at a higher end mag like say Vogue or a similar catalog from Eddie Bauer, pay close attention to the detail in the photos. There's a real art to making the viewer feel as though they can feel the texture of the fabric, the shadow areas have ample detail and the highlighted areas are clean and sharp.
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