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Group: Moderators
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| Did you ever wonder why newer cameras are recording images at increasingly and staggering larger sizes (poster size... literally)? Or why even the best cameras record JPEGs at 72dpi when print work is recommended at 180 dpi or higher (300+ dpi really for best viewing)? What exactly is dpi (dots per inch) and what is at issue here? Basically... most hobbyists are shooting JPEG by default or preference. It is true... TIFFs are better quality since they are not compressed files, and RAW format is even better for photo manipulations - but these are advanced topics and not the norm for the typical aquatic photog or their camera settings. The JPEG is a computer file format that is pc/Web friendly (small sized, compressed form... image quality). With your digital view essentially limited to 72 dpi max, it is all good for on screen viewing. Print work, however (printed photos, magazines, books, etc) demands better resolution... more detail/information (dots on the page) to be visually pleasing... hence the recs for 180 dpi minimum and 300 dpi+ for really knock out sharpness. On the compuer screen... you don't have 300 pixels per inch! But on the printed page... you are freer with advanced print heads/technology. So a good rule of thumb is that with a satisfactory JPEG (shot and/or cropped in composition you'd like to see printed) in hand at 72 dpi, you can print that pic on the page at 1/4 of its original size (the 72 dpi JPEG captured by the camera). By shrinking the image a factor of 4, you can increase the resolution=number of dots per inch (4 X 72 dpi) to improve the print quality (same image... same dots/details... just in a smaller space and looking more detailed for it, in layman's terms) An example: Lets say an 8-megapixel camera shoots a JPEG image at roughly 3 meg in (memory) size with a resolution of 2304 X 3456 (or 32" X 48" on your computer screen... huge!). To print this "poster" on paper (book or magazine page for example) at 1/4 size (8" X 12") we can get 288 dots per inch (dpi) on that 8X12" page by keeping the same number of pixels (2304 X 3456 morsels of data/detail) but reducing the canvas (viewed/printed page size to 8" X 12"). When you open your photoediting software such as PhotoShop, you can see these specs and toggle them to explore the results of size and resolution. Does this make sense to y'all? Any questions?
. Anthony Calfo
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Last Login: 10/19/2009 7:27:56 AM
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Perfect Anthony,
When you open your photoediting software such as PhotoShop, you can see these specs and toggle them to explore the results of size and resolution.
One other issue for beginers to think about is "How big should my photo be on the web when space is an issue." I use 72dpi for all my web picts. Photoshop has a nifty "Save for Web" function in the file menu. This automatically reduces file size (Mb's) so you get the best possible picture out on the internet without too large of a file.
I usually reduce the original NEF file, 300dpi (this is a raw file) to 72dpi and then save for web.
The file can go from 17.2 Mb to 219k for internet viewing.
FWIW,
Tom
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Group: Moderators
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| excellent point about web sizes and viewing Tom. Indeed... 72dpi and just a couple/few hundred kb (a tiny file) is all that is needed for most good web pics. That "save for web" feature in Adobe PS is excellent... good reminder!
. Anthony Calfo
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And, if your photos are headed toward print, be sure to talk to your printer about what dpi the paper your publisher has chosen for your book can handle. Remember what those dots in dpi stand for: dots of ink. What happens when you drip a dot of water onto a paper towel? The dot expands as the paper absorbs the ink. The same goes for the liquid ink they'll shoot at the paper in your book. If you have too many dots per inch, they will expand until they touch and you'll get one great big black stain on the page where your photo should be. Newsprint is really absorbent and that's why the dots in newspaper photos are spaced so far apart. Art book quality paper absorbs hardly any of the ink, which is why you can space those dots so close together.
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Andy
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Group: Moderators
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| fabulous... another excellent point. This largely explains (to the layperson) why one paper or printer will call for 180dpi as adequate resolution... but another printer or (quality of) photo paper will say that nothing less than 300dpi is "print quality" Very straightforward... the more actual dpi, the better the pic is likely to print/appear.
. Anthony Calfo
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so that is why C...the Journal looks so good. good quality photos coupled with good paper stock. this is my request for more photos in the magazine.
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Carl-
We are all stardust
Sun powered reef
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| Glad you're pleased with it Carl. Thanks for the kind words-- Christine
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