On Sat, Sep 12, 2009 at 12:27 AM, Michael J. M. wrote:

Hello all,

I experimented with the resolution settings in the gimp --> scale image menu.

The resolution does not seem to have any effect on the rendering of the image on a computer screen.

It has no effect on file size either.

I checked this by scaling and saving the same image in 3 different resolutions
(but no other changes):

72dpi, 300dpi, 600dpi.

When opening them again all were rendered at the same size on the screen.

I concluded that the dpi setting is only used by printers. Is this correct?

No, if you turn off View->Dot for dot then the DPI relative to your display DPI is used to scale your view of the image.

Hi

This is an interesting question also to me.

David Gowers wrote:

No, if you turn off View->Dot for dot then the DPI relative to your display DPI is used to scale your view of the image.

That much I had already found; but still, when I open a file that has been scaled only in resolution (for instance 300->700), still the different imageviewers display the same image.

I know that this is not a Gimp related question, and I feel that the Gimp's approach is correct; but still I don't understand the whole resolution thing completely. I take it many imageviewers simply don't have the capability of taking the resolution into consideration, when rendering an image. I'm I right?

Regards

Jaime

Jaime Seuma wrote:

Hi

This is an interesting question also to me.

David Gowers wrote:

No, if you turn off View->Dot for dot then the DPI relative to your display DPI is used to scale your view of the image.

That much I had already found; but still, when I open a file that has been scaled only in resolution (for instance 300->700), still the different imageviewers display the same image.

I know that this is not a Gimp related question, and I feel that the Gimp's approach is correct; but still I don't understand the whole resolution thing completely. I take it many imageviewers simply don't have the capability of taking the resolution into consideration, when rendering an image. I'm I right?

See if this helps:
http://www.scantips.com/basics01.html

Jaime Seuma wrote:

See if this helps:
http://www.scantips.com/basics01.html

Thank you for making this link available.

On Tue, Sep 15, 2009 at 9:40 AM, Patrick Horgan wrote:

Jaime Seuma wrote:

Hi

This is an interesting question also to me.

David Gowers wrote:

No, if you turn off View->Dot for dot then the DPI relative to your display DPI is used to scale your view of the image.

That much I had already found; but still, when I open a file that has been scaled only in resolution (for instance 300->700), still the different imageviewers display the same image.

A 400 pixel wide image will always have exactly 400 pixels across, so on any given display device it will show the same irregardless of the resolution. On a 70dpi device it will be 5.71 inches wide, on a 90dpi device it will be 4.44 inches wide, on a 300dpi device it will be 1 1/3 in.

If you set the dpi for the image to match the device you intend to show it on, then if, for example you change units on the bottom of the drawing window to inches, it will accurately report to you the sizes of things as you expect to display them.

It won't make it display any differently though.

In GIMP (and Photoshop, and some other editing software) it will make it display differently. If your display reports its size correctly and Dot for Dot is off, the image will display at the correct size, closely matching the original DPI (of course you do not get any more actual dots out of this -- it just means that the relative scale of things is correct).

It's easy to see this if you halve the DPI for one dimension (eg. so DPI == 36x72) and then turn off Dot for Dot

On a 300dpi device it will
still display as 1 1/3 in, even if you set the resolution to 70dpi.

This is true for most simple 'viewing' software, which doesn't scale the view to be accurate. Not for editors that try to be accurate, such as GIMP.

David

Thank you all for the tips and links, I think this is enough info to make me understand the whole thing, and to make me feel comfortable with it.

Best regards

Jaime

David Gowers wrote:

In GIMP (and Photoshop, and some other editing software) it will make it display differently. If your display reports its size correctly and Dot for Dot is off, the image will display at the correct size, closely matching the original DPI (of course you do not get any more actual dots out of this -- it just means that the relative scale of things is correct).

It's easy to see this if you halve the DPI for one dimension (eg. so DPI == 36x72) and then turn off Dot for Dot

On a 300dpi device it will
still display as 1 1/3 in, even if you set the resolution to 70dpi.

This is true for most simple 'viewing' software, which doesn't scale the view to be accurate. Not for editors that try to be accurate, such as GIMP.

David