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image resolution being changed by Gimp automatically?

Feb 2, 2012, 13:40
Post: #1
image resolution being changed by Gimp automatically?
Hi,
Apologies if this has come up elsewhere. I've found something very strange and can't see it referred to elsewhere.

I am opening some 300 dpi photographs, but when I go to the "scale image" dialog box in Gimp, the image resolution is listed by default as 72dpi !!

But the pictures were shot in high-res, and when you look at the file properties or open the image in Photoshop, they all confirm that it is a 300 dpi picture. Only Gimp is presenting it as 72dpi. It happens that the photographs are bw, but the colour mode is RGB, not greyscale.

Any idea what's going on here, and how I can stop Gimp downsampling the images automatically if that's what is happening?

Thanks!
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Feb 2, 2012, 14:41 (This post was last modified: Feb 2, 2012 14:48 by ofnuts.)
Post: #2
RE: image resolution being changed by Gimp automatically?
I don't know what you call a "300DPI photograph". Unless you are obscenely rich or a professional photographer, your camera sensor is at best at 1"x1.5" (24x36mm) so your picture would be 300*450 pixels... I assume that some software announces 300 DPI either because it's a default or because they see a 300DPI on the default printer. Gimp says 72DPI because that is your default setting (Edit/Preferences/Default image/advanced options).

Gimp doesn't downsample the image; otherwise it would have less pixels, and I assume you are still getting your 8/10/12/16Mpix which is what really counts.

Some reading (you aren't the first to wonder):

http://gimpforums.com/thread-basic-scali...90#pid6490
http://gimpforums.com/thread-resizing-an...11#pid1611

Now answering your questions on
https://Gimp-Forum.net
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Feb 2, 2012, 16:07
Post: #3
RE: image resolution being changed by Gimp automatically?
Hi,

Thanks for your speedy reply, and for the links you included.

I think I can see now where my confusion is coming from. The image is indeed 4288 x 2848px in both Photoshop and Gimp. But when you open the Image>Image Size dialog in PS the "document size" resolution for printing defaults to 300dpi. In the equivalent Gimp dialog it defaults to 72dpi. But as you point out, it's the same number of pixels showing on the screen in both cases.
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