Jaime Seuma schreef:

Hello

I use The Gimp to edit my photographs, which I shoot with a Canon EOS 50D. I shoot always RAW, and use the propietary Canon software (DPP) to process the pictures a bit before converting them to jpeg (max conversion quality) with a resolution of 350 dpi.

But when I open this jpg with the Gimp, either through the 'print size' dialog, the 'image scale' dialog or the 'image properties' dialog, seems to me that the Gimp takes it as 72 dpi resolution. Out of curiosity, I've just open the same image with both the Gimp and Photoshop Elements, and Elements states that it has a resolution of 350 dpi (as expected).

I had never noticed that! Thing is that every time I scale down an image, the Gimp sets 72 dpi as default for resolution.

All of my images are at this (low) resolution now (which doesn't matter as I've kept the original RAW files). I didn't notice this when I was working with the Gimp, till a few days ago that a friend told me -when I showed him my pics- that I should keep resolution higher when downscaling jpgs.

Am I missing something here? Any ideas?

I must confess that I have never worried about the resolution before, and I don't think I understand this issue completely.

TIA

Jaime

On Mon, Sep 14, 2009 at 4:12 PM, Jaime Seuma wrote:

I had never noticed that! Thing is that every time I scale down an image, the Gimp sets 72 dpi as default for resolution.

maybe the gimp selects the default dpi as set in edit->preferences->default image

All of my images are at this (low) resolution now (which doesn't matter as I've kept the original RAW files). I didn't notice this when I was working with the Gimp, till a few days ago that a friend told me -when I showed him my pics- that I should keep resolution higher when downscaling jpgs.

Am I missing something here? Any ideas?

I must confess that I have never worried about the resolution before, and I don't think I understand this issue completely.

As long as you are using pixels as units for rescaling there is no problem with the DPI.
GIMP works with pixels and thus the DPI is only an information so any program manipulating
the image can know its actual dimensions.

This is useful for example when printing or rescaling image to a "natural" size. You can always
change the DPI of the image without modifying the actual pixels.

Hi,

On Mon, 2009-09-14 at 16:12 +0200, Jaime Seuma wrote:

I use The Gimp to edit my photographs, which I shoot with a Canon EOS 50D. I shoot always RAW, and use the propietary Canon software (DPP) to process the pictures a bit before converting them to jpeg (max conversion quality) with a resolution of 350 dpi.

But when I open this jpg with the Gimp, either through the 'print size' dialog, the 'image scale' dialog or the 'image properties' dialog, seems to me that the Gimp takes it as 72 dpi resolution. Out of curiosity, I've just open the same image with both the Gimp and Photoshop Elements, and Elements states that it has a resolution of 350 dpi (as expected).

Most likely your software embeds the resolution information into the Exif metadata and fails to update the resolution in the JFIF header. That's a minor problem as the resolution is really just some arbitrary number and pretty much meaningless for photographs.

There is a bug report about the JPEG plug-in failing to recognize the resolution in the Exif data. If you care, feel free to provide a patch to fix this.

Sven