Leave it at 300 pixels per inch or upsize to 400?

[emil_ems5]

<p>I am currently working with converting some pictures for a book to be offset printed. Since the printer prints at 200 lines per inch, the resolution to be delivered is 400 pixels per inch. </p>

<p>It so happens that some of the pictures only manage 300 pixels per inch in natural resolution at the size to be printed. What is the best strategy in this case? Should I upsize the pixels to 400, using Photoshop's Bicubic Smoother Mechanism, or just include those prints at 300 pixels per inch in the PDF file to be delivered to the printer?</p>

[stephen_ray]

<p>Even if your printer's equipment is old, such as 20 years old, the most resolution necessary is about 1.25 - 1.5 x the line screen. Therefor, 300 ppi will be fine for your printer. 300 DPI has been a misnomer for at least 20 years now. Also know, PPI is not DPI.<br>

To learn more, Google search for Brian Lawler's essay paper:<br>

Resolving the resolution issue:<br />How many dpi does it to make an lpi?</p>

[digitaldog]

<p>You don’t need to double the resolution for that linescreen (2X quality factor). 1.5 is plenty. Below about 133lpi, a 2X quality factor is usually a good idea. Above that, you can easily get away with 1.5 or perhaps less. Leave em at 300ppi.</p>

[ellis_vener_photography]

<p>The other question is, will they be cropped?</p>

[bkkstudios]

What is the mathematics behind these numbers? I.e., why is 1.25-1.5x LPI a good number?

[digitaldog]

 

<blockquote>

<p>What is the mathematics behind these numbers? I.e., why is 1.25-1.5x LPI a good number?</p>

</blockquote>

 

<p>A 1:1 relationship of pixel to halftone dot isn’t going to produce acceptable quality output for one. Its less about math and more about sending X number of pixels to a device that produces a halftone dot using a certain linescreen and looking at the quality of the output. When the Linescreen is below about 133lpi, you need two pixels per dot or quality suffers. More buys you nothing. Above 150lpi, more than 1.5 buys you nothing. You can use 2X if you wish but don’t expect to see anything different on the press. </p>