Can pdf files be resized for printing without loss of resolution?

Question

I'm quoting a job that is 300 dpi at 3"x5" size but client wants it to print at a larger size (5.5”x7” or thereabouts). I’m concerned about loss of resolution if I print it at a larger size. When I look at the specs for a larger size of this image in PS it’ still shows 300 dpi.

I don’t really understand how pdfs work. Do they scale without loss of resolution?

Conrad_C · Accepted Answer

The reason PDF is confusing is because PDF can contain both vector data (fonts, paths) and raster data (pixel images). How well a PDF scales depends on the quality of the contents:

Type and vector data in the PDF will scale at full detail at any resolution.
Images in the PDF will appear more pixelated as you scale up the PDF, because a pixel image has a fixed resolution.

I had Acrobat open the PDF you attached, and had Acrobat pop open the embedded images in Photoshop. This revealed several problems with the attached PDF:

Photoshop says the two embedded images are far below 300 ppi to start with (highlighted at the bottom of the graphic below), so the type in the PDF is already not 300 ppi at print size; it looks fuzzy.
The reason the type is already not sharp is that the type was rasterized into an image. There are no editable text layers. If the type had been left as original text, it could have been scaled freely, but in its current pixel form it won’t scale well.

The ideal way to do this:

Make sure the original graphics are either vector, or at least 300 ppi at the final print size (which is now 5.5" x 7").
Go back to the original documents used to set the type, and add the graphics to them so that the type stays vector.
Don’t use any step that rasterizes the type, so that it remains freely scalable.
Export as PDF.

Also — if you used Image Size in Photoshop to preview scaling it up, and it said it was still 300 ppi, that’s probably because the Resample option was turned on. When Resample is on, Image Size will maintain or increase the resolution by “making up” additional resolution from the existing pixels, but that never looks as good as having full resolution graphics in the first place. If you want to see how ppi is really changing as you scale it up to 5.5" x 7", turn off Resample.

JJMack · Answer

If you resample a raster image you will loose image quality. You discard details you have for the image when you reduce the number of pixels you have for an image. If you increase the number of pixels you have to make up details you do not have for your image. Decreasing the number of pixels you have in a high quality print size document for use on the web works well. Increasing the number of pixels you have in a Web size image so you can print the image with small high resolution pixels does not work well if you greatly increase the number of pixels in a raster image. Only vector graphic images scale up and down in size well. The paths are generate via math and pixels are rendered to the Paths and the Areas they enclose.

Resolution is Pixel size. Displays have one size pixel they do not play the resolution game the have one resolution. Printers do play the game. You can print your X number of pixel wide by Y number pixels high image any size you want by changing the print pixels size. The Print DPI the pixels density the print resolution.

Set the print resolution around 180 to 190 DPI or change the height or width to the size you want and Photoshop will set the other side and dpi in the image size dialog with RESAMPLE NOT Checked.

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