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Old Oct 15, 2008, 5:56 PM   #1
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I want to change my 72 dpi photo to 300 dpi. I can't figure out how to do it so I can e-mail it as a jpeg file. I can do it as a pdf file, but it needs to be a jpeg file.

Any suggestions/help will be appreciated.

Thanks in advance.
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Old Oct 15, 2008, 6:09 PM   #2
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What are you trying to accomplish with it? You do realize that the dpi information you see is only a field in the metadata that really doesn't impact the image, right? IOW, it's just a number that the camera puts there. The actual dpi will depend on the resolution of the image in pixels and the size it's printed at.

For example, if you wanted an 8x10" image at 300dpi, you'd need to send an image size of 3000 x 2400 pixels (7.2 Megapixels) to the printer.

8 inches x 300 dpi = 2400 pixels
10 inches x 300 dpi = 3000 pixels.

But, if you tried to take that same 3000 x 2400 pixel image and print it at 16x20 inches, you'd end up with only 150 dpi:

2400 pixels / 16 inches = 150
3000 pixels / 20 inches = 150

The dpi you see is just a number in the image header. Some cameras plug in 72 dpi, some plug in 240, some plug in 300, etc. But, it doesn't mean a thing to most software.

Here is an article that may help to explain it:


If you've got someone that wants to see 300dpi in the header for some reason, you can probably find a way to edit it.

Phil Harvey's ExifTool can probably do it (although I haven't tried that with it), since it's a popular tool for viewing and editing metadata:


You can find a GUI front end for it here that works with Windows (but, you'll probably need to rename the exiftool.exe you download to exiftool.exe (I think it may have changed to something else in newer versions) so that the GUI can call it OK:


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