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Improve the quality of printed iPhoto books
Authored by: pub3abn on Jul 20, '05 11:09:44AM

Lines per inch (LPI) is the key to knowing the ideal dots per inch (DPI) for a given output device. Most book or magazine quality publications are either 150 or 175 LPI. A good rule of thumb is that nothing is to be gained from having the DPI of your photos beyond 1.5 to 2 times the LPI. So for 150 LPI, you don't need more than 225-300 DPI. For 175 LPI, you don't need more than 270-350 DPI. In both cases, 300 DPI is a good safe number. Without knowing the LPI of the printing press the iPhoto books are printed at, we just have to guess.

Of course, all of this assumes that you are NOT enlarging your images. If you increase the DPI of your images, you must also DECREASE the physical size proportionately, or else you are simply adding interpolated detail to your image ... which usually makes your image look blurry/jaggy/etc. The easiest way to do this in Photoshop is to open the Image Size dialog, uncheck "Resample Image" at the bottom, and then enter 300 pixels/inch in the Resolution field. Notice that the numbers in the width and height fields will shrink. You now have the ideal size of your image at 300 DPI. You can enlarge it if you want, but realize that the quality will suffer. Moral: Always use the highest resolution originals that you can get. For full-page (8.5 x 11) pictures in a coffee-table book, you really need an 8-10 megapixel camera.

I've never ordered a book from iPhoto, and I've never tried this technique of tweaking the plist settings, but I do concur that 300 DPI is the least you would want for large, professional looking images. And if you are particular and have the know-how to pull it off, sending your images as CMYK (instead of RGB) from a calibrated system should give you much better/more predictable results too.

Footnote: For one-bit images, the resolution of the output device, not the LPI, is the key. But this does not apply to RGB or CMYK images.



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Improve the quality of printed iPhoto books
Authored by: pub3abn on Jul 20, '05 11:16:49AM

For the curious, I will explain my statement: "For full-page (8.5 x 11) pictures in a coffee-table book, you really need an 8-10 megapixel camera."

The math is this:

8.5 (inches) x 300 (dpi/ppi) = 2550 (pixels).
11 (inches) x 300 (dpi/ppi) = 3300 (pixels).

2550 x 3300 = 8,415,000 pixels, or just over 8 megapixels.

Of course, if you crop the image at all, you need even more pixels.



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