Expert: Ken Black - 11/19/2009

Question
I have a lot of PDF files saved on DPI 150-300. All I need to unify the DPI i.e. 300. But I don't want to scan files again to save huge time. So is there any way to chnage the DPI of already saved PDF, like 150 DPI change into 300 DPI?

Thanks,

Answer
Hi Kamran Khan,

Unfortunately, you are pretty much stuck. You could change the resolution of the pdf by rasterizing it in Photoshop or another image editor, and set its resolution to 300 dpi, but you will only end up with a larger file with the same low quality.

Once something has been made low resolution, there really isn't an easy way to increase the resolution, other than making the image smaller. As an image's size decreases it's effective resolution will increase.

For example, if your image is 8" x 10" at 150 dpi, if you resize the image to 4" x 5", the effective resolution at reproduction (printing) will be 300 dpi.

There are some software products available that can enlarge and allow you to gain in resolution. Genuine Fractals Print Pro, a plugin for Photoshop, can do this usually with pretty good results. The key thing to consider is if it looks like garbage going in, it will look like garbage coming out, only larger. Genuine Fractals is available from onOne software, here:
http://www.ononesoftware.com/detail.php?prodLine_id=7

Photoshop can give you some help when attempting to enlarge images by using the algorithm "Bicubic Smoothing" when re-sampling images. In your, case however, the results likely will not be what you are looking for and that is why I don't typically recommend this method.

I hope that helps,

Thanks,

Ken Black

www.bestprintingonline.com