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Question
Good day
Is it possible to make images and photos greater than 300 dpi in photoshop and how different would a 600 dpi be than a 300 dpi. Is so what would be maximum dpi and what type of situations and applications use dpi's greater than 300 dpi.
Finally where and how does one print images greater than 300 dpi - most printers dont.

Answer
Hello!

Your question slightly reflects a widely held misconception about DPI! An image file is nothing more than a matrix of colored pixels. The initial horizontal and vertical pixel counts of that matrix are determined by the megapixel rating and resolution setting of your camera. Images created by digital cameras have no DPI parameter... only a discrete number of discrete pixels in both the horizontal and vertical directions.

Of course, you can then "upscale" or "downscale" an image's size using Photoshop's Image > Image Size > Resample Image setting (with Constrain Proportions selected). This applies mathematical interpolation to increase or decrease the actual number of pixels in the image matrix, but Photoshop itself does not control any "dot-per-inch" image parameter.

That's because DPI is strictly an output parameter! It's the resolution at which a printer outputs the image's pixel matrix onto paper or some other medium. In Photoshop's Image > Image Size window, if you deselect the Constrain Proportions box, enter a different value in the Resolution field, and click OK, Photoshop actually does nothing to the image itself. It simply tells you what its output dimensions would be if it were printed at the new dot-per-inch resolution you entered.

And your question seems to indicate that you are aware of all this. But I wanted to clarify it for others who might need to know.

You seen more interested, in fact, in the effects of DPI on image quality.  Most photo printers (including your local lab or drugstore) prefer to output images at either 240 or 300 DPI. And you can estimate how big an image will print on their equipment by opening the image in Photoshop, deselecting Constrain Proportions, and entering the DPI resolution that the company printing your photo plans to use. (And if you have a local lab, and want to output an image at (say) 600 DPI, go ahead and ask them! My little mom-and-pop lab just down the street can do it, so yours should too.)  

Similarly, you can use Photoshop to estimate the size of an image that's output on your home printer... at any DPI resolution it supports. My printer can go up to 1800 DPI, but yours may have a different maximum.

Changing your printer's DPI setting will indeed affect both the output image's size and its quality. Reducing the printer's DPI/resolution will produce larger prints that eventually look decreasingly sharp. (Some photographers output at only 72 DPI when they want a mural-sized print. And in that case, their print may look terribly pixelated when viewed up close, but just fine from farther away.)

Similarly, increasing the output DPI from 300 to 600 or more will result in ever smaller prints that may look increasingly sharp, but decreasingly detailed. (An old photographers' trick for fixing slightly "soft" images is to print them smaller... using a higher DPI resolution.)

But the medium you print on also affects apparent output quality. Non-glossy paper, for instance, allows inkjet droplets to "spread" more than glossy paper. And as a result, while an inkjet print at 300 DPI may look wonderful, the same 300-DPI print on non-glossy paper may look "caked" or "blotchy." And even 1800 DPI can be used on mylar, glass, or another low-spread medium.

And your last question ("where and how does one print images greater than 300 dpi - most printers dont." ) raises a counter question in my mind! By printing at greater than 300 DPI, are you hoping to produce a larger print or a smaller one? If smaller , then you will get what you want. But if larger , you'll need to either reduce the output DPI to get the larger print... or add many more pixels to the image file itself with Photoshop's Resample Image, and then print at 300 DPI or higher.

I certainly hope this helps!

Sincerely,

Dave

Photography

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Dave Powell

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My specialty is highly atmospheric digital-infrared photography, and I'd love to answer questions about digital-IR equipment and procedures. I can also help people understand classic "old-photog" techniques (like "Sunny 16 Exposure" and "Hyperfocal Focusing")... which are still useful today. I can answer questions about processing, improving, manipulating, and printing digital photos with programs like Photoshop. I'm an inveterate tinkerer, and may be able to answer questions about making one's own photo equipment (such as DIY special-effect filters, close-up adapters, and pin-hole cameras); about doing super-closeup macro photography (film or digital); and about using older lenses on cameras made by different manufacturers (such as Nikon lenses on Canon bodies and Pentax lenses on Olympus bodies. I can answer general purchasing questions, such as "Can any of the digital SLRs use my old Minolta film lenses?" But as others have noted, nobody can identify the "best" camera for another person. That calls for extensive web research plus hands-on time in a good camera store. (But I can point to great web resources for doing this research!)

Experience

Over the past 40 years, I've used a huge variety of film cameras (SLR, rangefinder, point-and-shoot, high-end, fantastique-plastique, fully manual, highly automated, 35mm, 110, medium format, Polaroid, folding, even homemade pinhole). I've used digital cameras since the late 1990s (began when I was writing user manuals for Polaroidís digital cameras). I've also won juried photo competitions in the Boston area, and have exhibited and sold original prints. (Amazingly, my best-selling print was taken with a lowly 0.8-megapixel camera, and very carefully processed to print at 12x18 inches!) Iíve taught local adult-ed classes about digital cameras, Photoshop image processing, and better photography through self-understanding. Iíve contributed to Popular Photographyís tips and tricks column, and am currently writing a book about taking better photos through self-understanding.

Publications
Popular Photography (tips and tricks column), plus dozens of magazines and blog sites that have carried my bylined articles about computers, networking, information security, and eLearning.

Education/Credentials
Masters in Science Communications, Boston University, 1980. Bachelors in Mathematics, Denison University, 1970.

Awards and Honors
I've won several juried photo competitions in the Boston area, and have exhibited and sold original prints... especially digital-infrared landscapes, architectural abstracts, and cityscapes. I've also won multiple international awards in the technical-writing field... including a business press equivalent of the Pulitzer Prize. And I've even written for Sesame Street!

Past/Present Clients
Winchester Recreation Department (taught photography classes) Jenks Senior Center (taught photography and Photoshop classes) Polaroid (wrote their digital-camera user manuals until they entered Chapter 11)

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