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All PDF's appear to be 72 dpi, no matter what


Question

I'm having some trouble creating a PDF with Photoshop.

The client wants the final file to be "a PDF at 300 dpi".

I have an image (3300 x 2550 pixels @ 300 dpi) in Photoshop. (11" x 8.5" canvas)

It seems that no matter which method or setting, my PDF is always saved at 72 dpi because the PDF ends up at 792 x 612 pixels every single time.

I'm using Photoshop CS2 on a Mac. I've tried a "save as PDF" from the file menu and I've also tried a "save as PDF" from the print dialog box.

I even saved it as a TIFF (3300 x 2550 @ 300 dpi) and opened in GraphicConvertor, then saved as a PDF. Same problem... the PDF is only 72 dpi (792 x 612 pixels).

So how can I get the final PDF size to be 3300 x 2550 pixels @ 300 dpi?

2012/02/20
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2/20/2012 5:57:00 PM

Accepted Answer

Original File: 3300 x 2550 pixels @ 300 dpi (11 x 8.5 inches)

Now I believe that my conclusions based on observations were incorrect.

1) In Mac OS X.4.11, "Get Info" on the PDF simply shows "792 x 612" without units. (In pixels, compared to my original, this would calculate to be 72 dpi).

2) In Mac OS X.6.8, "Get Info" on the PDF shows no dimensions. In the Preview App (Menu > Tools > Show Inspector), it shows 792 x 612 points and 11 x 8.5 inches. There is nothing about "dpi" here.

So this is why I posted the question here. It appeared as if all PDF were being converted to 72 dpi no matter how I saved them.


Then I opened the suspect PDF in Acrobat Pro.

Menu > File > Properties > Description tab shows a page size of 11 x 8.5 inches. Nothing else listed there regarding pixel or point size. Also, there is nothing there about dpi.

However, there is a button labeled "Additional Metadata". Under the item called "Camera Data 2", there it is: Pixel Dimension X: 3300, Y: 2550, Resolution X: 300, Y:300, and Resolution Unit: Inch.

So it appears that these PDF's are not 72 dpi after all.

Yes, I realize pixels are not the same as points. My confusion was caused by how the information is presented by the Mac OS (Get Info, Preview, etc.) when inspecting the PDF files. You'd think the pixel dimensions and dpi would be prominently displayed as it is for image files.

2012/02/08
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2/8/2012 9:51:00 PM

You figured it out. The dimensions you see in Bridge for the PDF are the output dimensions in points, not the image size in pixels.

This is a sometimes misleading side effect of the fact that PDF is (in theory) resolution-independent, much as an Illustrator or EPS document is, that the "dimensions" of the PDF shown in Bridge are the print dimensions, not the pixels. Raster information in the PDF is, of course, at a particular resolution determined at the time the PDF is created. It could be 100 ppi or 1200 ppi; the document dimensions would be the same.

A "300 dpi PDF" is a document that contains raster information sized to 300 ppi at the specified output dimensions.

2012/02/08