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why does photoshop 7 open a pdf file in 72 dpi when it was saved as 300 ppi and does this 72 now effect the printing quality?

why does photoshop 7 open a pdf file or a psd file in 72 dpi when it was saved as 300 ppi and does this 72 now effect the printing quality? I need to keep the quality level high enough for printing, and so I need to know 1. why does photoshop 7 change the dpi to 72
2. if I just change the dpi back to 300 will it print ok?
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Chris StanyonCommented:
When you open a PDF in Photoshop it prompts you for the resolution. Just set it to 300 dpi and open it.
<if I just change the dpi back to 300 will it print ok?> The short answer is yes.
Despite what you hear 300dpi (dots per inch or pixels per inch [same thing]) is still the standard for printing in the major publishing houses -- it's perceived to be the maximum detail that the human eye can perceive.
The dpi is really a 'print reference' -- it's a juggle between how many pixels you have in total and what size your image will print at.
Here's a good way to see all this without having to read technical explanations.
Just load an image into Photoshop and click Image / resize . Check the 'constrain proportions' box but UNTICK the 'Resample Image' box.
Now you can play with the dpi -- notice that everytime you change it, it changes the width and height of the 'print size' or 'document size' of the image. So with a 72 dpi  high resolution image you're going to have this huge blurry image (because it's stretching the pixels over a single page at only 72dpi) and the whole  image now won't even fit on the page -- so it crops it. You can see all this happening by additionally pressing 'print preview'.
But because, if you're printing, you always want 300dpi, it's a very good way to see exactly what size your image will print at using the full 300dpi.
Say you had a shot that you wanted for a 'cover shot' for a magazine, but you weren't sure if you had enough pixels in the shot to 'cover the cover' -- you simply select 300dpi and take a look at the print preview. The guys in the mag pre-press are always very reluctant to blow up a shot that won't go over the whole cover at 300dpi, because they have to stretch the pixels -- and then it starts to blur.

You probably know that 72 dpi is a computer monitor standard -- ok for web pages.

Yes Bong no comment was added for 21 days; in fact no comment has been added for 601 days, or
one year 7 months and 23 days. Good to look back anyway.
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